An ovarian cyst is a fluid-filled sac that develops on or within the ovary, most commonly arising from follicular development or corpus luteum formation, and is often benign and self-limiting.

Exam domain	One-glance essentials
Definition / diagnosis	*An ovarian cyst is a fluid-containing ovarian lesion; most in reproductive-age patients are functional and benign* ^[1]^[2] Classify by simple versus complex morphology, physiological versus pathological origin, and menopausal status ^[1]
Epidemiology / risks	Functional cysts occur with ovulation; endometriosis predisposes endometrioma and pregnancy may reveal corpus-luteum cysts ^[1]^[2] Malignancy risk rises after menopause and with complex, solid, papillary, vascular, bilateral, or persistent lesions ^[1]
Core mechanism	Follicular or corpus-luteum persistence creates functional cysts; pathological lesions arise from epithelial, germ-cell, stromal, or metastatic tissue ^[1] Increasing size and mobility raise risk of torsion, rupture, haemorrhage, or pressure ^[2]
Clinical picture	Most are asymptomatic; pain, pressure, bloating, dyspareunia, or menstrual symptoms may occur ^[1]^[2] Sudden severe unilateral pain with nausea suggests torsion or rupture; instability suggests significant haemorrhage ^[1]
Investigations	Pregnancy test and TVUS are first-line; describe size, septa, solid areas, papillae, Doppler flow, ascites, and bilaterality ^[1]^[2] Use tumour markers and CT or MRI selectively according to age, morphology, and malignancy risk ^[1]
Management	Observe many small simple premenopausal cysts with appropriate follow-up; persistent, symptomatic, large, complex, or suspicious lesions need specialist surgery or oncology review ^[1]^[2] Preserve ovarian tissue when safe in young patients; urgent surgery is required for torsion or uncontrolled haemorrhage ^[1]
Complications	Complications are torsion, rupture, haemorrhage, infection, pressure symptoms, infertility, and malignancy ^[1]^[2] Surgery may reduce ovarian reserve or spill occult malignancy if poorly planned ^[1]
Prevention / follow-up	Use structured ultrasound follow-up and clear return advice for acute pain or increasing symptoms ^[1] Genetic risk assessment is appropriate when family history suggests hereditary ovarian cancer ^[2]
Exam traps	*Simple cysts and polycystic ovarian morphology are not the same as PCOS* ^[1] Normal Doppler flow does not reliably exclude torsion, and CA-125 is not a stand-alone discriminator of benign versus malignant disease ^[1]^[2]

References

^[1] Lecture slides: GC 118. Pelvic mass ovarian cancer and cysts; uterine fibroid; pelvic imaging.pdf (pp. 12, 20, 24 — ovarian cysts) ^[2] Lecture slides: Block C - Pelvic mass_ ovarian cancer and cysts; uterine fibroid; pelvic imaging.pdf (pp. 8–10, 15 — cyst assessment)

Ovarian Cyst

An ovarian cyst is any fluid-filled sac arising from or within the ovary, typically ≥ 1 cm in diameter. The term encompasses a broad spectrum of pathology — from entirely physiological, self-resolving functional cysts that are part of normal ovulation, all the way to neoplastic cysts (benign or malignant). The clinical importance lies in distinguishing the harmless from the dangerous.

Etymology: "Ovarian" = pertaining to the ovary (Latin ovarium, from ovum = egg); "Cyst" = from Greek kystis = bladder/sac. So literally, a "sac on the egg-producing organ."

Key Conceptual Point

Not all ovarian cysts are pathological. The dominant follicle before ovulation and the corpus luteum after ovulation are both, technically, "cysts." They become clinically relevant only when they persist, enlarge, cause symptoms, or develop features suspicious of malignancy.

Extremely common: Ovarian cysts are found incidentally in up to 18% of postmenopausal women and are even more frequent in premenopausal women on imaging.
Functional cysts are the most common type overall, occurring in virtually all ovulating women at some point.
Mature cystic teratoma (dermoid cyst) is the most common benign ovarian neoplasm, accounting for ~10–20% of all ovarian tumours. Peak incidence: reproductive age (20–40 years).
Epithelial ovarian tumours (serous and mucinous cystadenomas) become more common with advancing age, peaking in the 40s–60s.
Endometriotic cysts ("chocolate cysts") affect ~17–44% of women with endometriosis.
In Hong Kong, ovarian cancer ranks as the 6th most common cancer in women (Hong Kong Cancer Registry data), with epithelial ovarian cancer being the predominant histological type.

Risk Factor	Mechanism / Explanation
Reproductive age	Active ovulation → functional cysts are physiological
Endometriosis	Ectopic endometrial tissue implants on ovary → forms endometrioma
PCOS	Anovulation → multiple small follicles arrested at 2–9 mm ("string of pearls")
Ovulation induction (e.g. clomiphene, gonadotropins)	Hyperstimulation → theca lutein cysts (multiple, bilateral)
Tamoxifen	Weak oestrogen agonist effect on ovary → functional cysts
Smoking	Associated with functional cysts (altered HPO axis)
Tubal ligation / hysterectomy	Altered ovarian blood flow → may predispose to cyst formation
Early menarche / late menopause	Prolonged ovulatory lifespan → increased cumulative risk
Family history of ovarian/breast cancer (BRCA1/2)	Risk of malignant ovarian neoplasms (but these can also present as "cysts")
Obesity, insulin resistance	Associated with PCOS and anovulatory cysts ^[1]^[2]

4. Anatomy and Functional Review

Paired organs, almond-shaped, ~3 × 2 × 1 cm in the reproductive-age woman, located in the ovarian fossa on the lateral pelvic wall (bounded by the external iliac vessels above and the ureter and internal iliac artery behind).
Attachments:
- Mesovarium — posterior leaf of the broad ligament; contains ovarian vessels
- Suspensory (infundibulopelvic) ligament — carries the ovarian artery and vein from the aorta/IVC (right) and renal vein (left) to the ovary
- Ovarian ligament (proper) — connects ovary to uterine cornu (does NOT contain major vessels)
Blood supply: Ovarian artery (branch of abdominal aorta at L2) + anastomosis with uterine artery branch. Venous drainage: right ovarian vein → IVC; left ovarian vein → left renal vein.
Lymphatic drainage: Para-aortic lymph nodes (because of embryological gonadal origin from retroperitoneum).

Layer	Components	Clinical Relevance
Surface epithelium (modified peritoneal mesothelium)	Single layer of cuboidal/columnar cells	Origin of epithelial tumours (serous, mucinous, endometrioid, clear cell) — the most common group of ovarian neoplasms
Cortex (stroma + follicles)	Primordial → primary → secondary → Graafian follicles; theca and granulosa cells	Origin of sex cord-stromal tumours (granulosa cell tumour, fibroma, thecoma) and functional cysts
Medulla	Loose connective tissue, hilar cells, blood vessels, nerves	Rarely gives rise to tumours

Understanding the normal cycle is essential because functional cysts are just exaggerations of normal physiology:

Follicular phase: FSH recruits a cohort of follicles → one dominant follicle emerges (reaches ~20 mm), producing oestradiol.
Ovulation: LH surge → follicle ruptures → oocyte released.
Luteal phase: Ruptured follicle becomes the corpus luteum → produces progesterone (and some oestrogen). If no pregnancy, it involutes into the corpus albicans by ~day 14 post-ovulation.

A follicular cyst = dominant follicle that fails to ovulate and keeps growing. A corpus luteal cyst = corpus luteum that fails to involute, fills with blood, and enlarges.

5. Aetiology and Classification

This classification from the lecture slides is high-yield and must be memorised:

Type	Entities
Functional	Follicular cyst, corpus luteal cyst, theca luteal cyst
Inflammatory	Endometriotic cyst, tubo-ovarian abscess
Germ cell	Mature teratoma (dermoid cyst)
Epithelial	Serous cystadenoma, mucinous cystadenoma, clear cell cystadenoma
Sex cord-stromal	Fibroma, thecoma
Others	Ovarian ectopic

High Yield Classification

This table directly from the lecture is the framework you should use when asked "What are the causes of ovarian cyst?" in an exam. Classify by type (functional → inflammatory → neoplastic by cell of origin) rather than just listing randomly.

5.2 Detailed Aetiology and Pathophysiology

5.2.1 Functional Cysts

These arise from the normal ovulatory process gone slightly awry. They are the most common ovarian cysts. By definition, they are non-neoplastic and usually self-resolve within 1–3 menstrual cycles.

Pathophysiology: A Graafian (dominant) follicle fails to rupture or fails to undergo atresia → continues to be stimulated by FSH/LH → accumulates follicular fluid → enlarges (typically 3–8 cm, can reach up to 10 cm).
Lined by granulosa cells (which produce oestrogen), so a large follicular cyst can produce enough oestrogen to cause:
- Menstrual irregularity (oestrogen suppresses FSH via negative feedback → anovulation → delayed or missed period, followed by withdrawal bleed)
- Breast tenderness
Usually unilateral, unilocular, thin-walled, anechoic on ultrasound.
Natural history: Most resolve spontaneously within 4–8 weeks as hormonal support wanes.

Pathophysiology: After ovulation, the corpus luteum normally fills with a small amount of blood (corpus haemorrhagicum). If bleeding into the cavity is excessive or resorption fails, it forms a corpus luteal cyst (typically 3–10 cm).
Lined by luteinised granulosa and theca cells → produces progesterone (and oestrogen).
Can cause a delayed period (progesterone maintains the endometrium, mimicking early pregnancy) → important DDx of ectopic pregnancy!
More likely to be haemorrhagic (internal echoes on USS, "lace-like" reticular pattern of fibrin strands) and more prone to rupture than follicular cysts.
Rupture → haemoperitoneum → acute abdomen (see Complications).

Pathophysiology: Overstimulation of ovarian follicles by high levels of β-hCG or exogenous gonadotropins → massive luteinisation of theca cells → bilateral, multiple, large cysts (can be massive, up to 20–30 cm).
Causes of high β-hCG:
- Gestational trophoblastic disease (hydatidiform mole, choriocarcinoma)
- Multiple pregnancy
- Ovarian hyperstimulation syndrome (OHSS) — iatrogenic, from IVF/gonadotropin therapy
These usually resolve once the hCG stimulus is removed (e.g., after evacuation of molar pregnancy).

Exam Trap

Students often confuse corpus luteal cyst with ectopic pregnancy because both present with a delayed period and adnexal mass. Always do a β-hCG in any reproductive-age woman with pelvic pain and a missed period.

5.2.2 Inflammatory Cysts

Pathophysiology: Ectopic endometrial glands and stroma implant on the ovarian surface → undergo cyclical menstrual bleeding (oestrogen-dependent) → blood collects within the ovary forming a "chocolate cyst" (thick, dark-brown, old blood = haemosiderin-laden, denatured blood that looks like melted chocolate).
Typically unilateral or bilateral, thick-walled, with homogeneous low-level internal echoes ("ground glass" appearance on USS).
Associated with endometriosis elsewhere (dysmenorrhoea, dyspareunia, dyschezia, infertility).
Does NOT resolve spontaneously — requires medical (hormonal suppression) or surgical (excision/drainage) management.
Malignant transformation: Small risk (~1%) of transformation into endometrioid or clear cell carcinoma of the ovary (particularly in longstanding, large endometriomas).

Pathophysiology: Ascending infection (usually from PID — Neisseria gonorrhoeae, Chlamydia trachomatis, polymicrobial) → involves the fallopian tube (salpingitis) → spreads to and involves the ovary → a walled-off collection of pus forms, incorporating the tube and ovary.
Presents with fever, severe pelvic pain, adnexal tenderness, cervical motion tenderness, and elevated inflammatory markers.
Important to distinguish from a simple ovarian cyst because TOA requires antibiotics ± drainage, not simple observation.

5.2.3 Benign Neoplastic Cysts

These are true neoplasms — they grow autonomously and do not resolve with observation (unlike functional cysts). Classified by cell of origin.

Pathophysiology: Arises from totipotent germ cells that undergo differentiation into mature tissues from all three germ layers (ectoderm, mesoderm, endoderm). Hence, can contain:
- Ectodermal derivatives: Skin, hair, sebaceous glands, neural tissue
- Mesodermal derivatives: Bone, cartilage, fat, muscle
- Endodermal derivatives: Thyroid tissue (struma ovarii), GI mucosa
Usually unilateral (bilateral in ~10%), well-encapsulated, slow-growing.
Imaging:
- AXR: tooth-shaped radiodensity (calcified teeth/bone) in the pelvis ^[3]
- USS: variable appearance depending on content — may show "dermoid plug" (Rokitansky nodule), fat-fluid level, hair ^[3]
- CT/MRI: definitive diagnosis, especially when fat content is demonstrated ^[3]
Complications:
- Torsion — dermoids are the most common ovarian tumour to undergo torsion (because they are heavy, pendulous, and mobile)
- Rupture → chemical peritonitis (sebaceous material is intensely irritant)
- Malignant transformation (~1–2%, usually squamous cell carcinoma in postmenopausal women)
- Struma ovarii → can cause hyperthyroidism (functional thyroid tissue)

"Teratoma" → Greek teras = monster + -oma = tumour. Named because these tumours can contain a monstrous mix of hair, teeth, and bone.

Serous cystadenoma:
- Most common benign epithelial ovarian tumour.
- Thin-walled, unilocular, contains clear, straw-coloured fluid.
- Lined by ciliated tubal-type epithelium (resembling fallopian tube lining).
- Usually moderate size (5–15 cm). Bilateral in ~20%.
- Malignant counterpart: serous cystadenocarcinoma (most common ovarian malignancy overall).
Mucinous cystadenoma:
- Can become very large (up to 30–40 cm, filling the entire abdomen — historically the largest tumours in medicine).
- Multilocular (multiple septated locules), filled with thick, gelatinous, mucin-rich fluid.
- Lined by mucin-secreting columnar epithelium (resembling endocervical or GI epithelium).
- Usually unilateral.
- Complication: If ruptured → pseudomyxoma peritonei (mucinous ascites with peritoneal implants — "jelly belly"). This is actually more commonly from appendiceal mucinous tumours, but ovarian mucinous tumours are a classic association.
Clear cell cystadenoma:
- Less common. Contains clear cells with glycogen (hence "clear" on histology — PAS-positive, diastase-sensitive).
- Strong association with endometriosis (may arise from endometriotic cysts).

Fibroma:
- Solid tumour of ovarian stromal fibroblasts (though may have cystic degeneration).
- Non-functional (does not produce hormones).
- Meigs syndrome = ovarian fibroma + ascites + right-sided pleural effusion. Why right-sided? Because peritoneal fluid preferentially tracks through transdiaphragmatic lymphatics on the right side.
- Removal of the fibroma → resolution of ascites and effusion (curative).
Thecoma:
- Arises from theca cells of the ovarian stroma.
- Functional — produces oestrogen → may cause abnormal uterine bleeding, endometrial hyperplasia, or even endometrial cancer.
- Almost always benign.
- Predominantly postmenopausal.

Ovarian ectopic pregnancy: Implantation of a fertilised ovum on the ovary itself (very rare, ~3% of ectopic pregnancies). Presents as an adnexal mass with positive β-hCG ^[1].

6. Relevant Classification Systems

Type	Examples	Hormone Production
Non-functional	Follicular cyst (small), fibroma, cystadenoma, teratoma	No hormone excess
Functional (oestrogen-producing)	Large follicular cyst, thecoma, granulosa cell tumour	Oestrogen → menstrual irregularity, endometrial hyperplasia
Functional (progesterone-producing)	Corpus luteal cyst	Progesterone → amenorrhoea, pregnancy-like symptoms
Functional (androgen-producing)	Sertoli-Leydig cell tumour	Androgens → virilisation
Functional (hCG-related)	Theca lutein cyst	Response to hCG, not producing hormones per se

This distinction is critical for management:

Feature	Simple Cyst	Complex Cyst
Walls	Thin, smooth	Thick, irregular
Septae	None (unilocular)	Present (multilocular)
Contents	Anechoic (clear fluid)	Mixed echogenicity, solid components, debris
Vascularity	None within cyst wall	Vascularity within solid/septal components
Papillary projections	Absent	Present → raises concern for malignancy
Typical dx	Functional cyst, simple serous cystadenoma	Endometrioma, teratoma, malignancy

USS findings of a simple cyst: anechoic, avascular ^[3]

The RMI is used to triage ovarian masses, particularly in postmenopausal women, to determine the likelihood of malignancy and guide referral.

RMI I = Ultrasound score (U) × Menopausal status (M) × CA125 level

Component	Scoring
Ultrasound score (U)	0 points if 0 features; 1 point if 1 feature; 3 points if ≥ 2 features. Features: multilocular, solid areas, bilateral, ascites, metastases
Menopausal status (M)	1 if premenopausal; 3 if postmenopausal (postmenopausal = ≥ 1 year amenorrhoea or age ≥ 50 after hysterectomy)
CA125	Absolute value in U/mL

RMI I < 200 → low risk of malignancy RMI I ≥ 200 → increased risk of malignancy → CT scan (abdomen and pelvis) → Referral for gynaecological oncology MDT review ^[1]

High Yield: RMI Algorithm for Postmenopausal Ovarian Cyst

For a postmenopausal ovarian cyst (≥ 1 cm): ^[1]

Measure CA125
TVS + TAS (transvaginal + transabdominal scanning)
Calculate RMI I

RMI I < 200 (low risk):
- Cysts fulfilling ALL of: asymptomatic, simple cyst, < 5 cm, unilocular, unilateral → consider conservative management (usually bilateral) → repeat assessment with CA125, TVS + TAS
- Cysts with ANY of: symptomatic, non-simple features, > 5 cm, multilocular, bilateral → MDT review → consider laparoscopic BSO (bilateral salpingo-oophorectomy)
RMI I ≥ 200 (high risk):
- CT scan (abdomen and pelvis)
- Referral for gynaecological oncology MDT review
- High likelihood of ovarian malignancy → Laparotomy: full staging procedure by a trained gynaecological oncologist
- Low likelihood of ovarian malignancy → Laparotomy: pelvic clearance (TAH + BSO + omentectomy + peritoneal cytology) by a suitably trained gynaecologist

7. Clinical Features

Many ovarian cysts are asymptomatic and found incidentally on imaging. When symptoms occur, they are due to mass effect, hormonal activity, or complications (torsion, rupture, haemorrhage, infection).

Symptom	Pathophysiological Basis
Asymptomatic / incidental finding	Small cysts (< 5 cm) do not distort pelvic structures and produce no hormonal excess
Pelvic pain / lower abdominal discomfort	Stretching of the ovarian capsule by the expanding cyst → activation of visceral nociceptors. Dull, aching, unilateral
Pelvic pressure / heaviness	Mass effect of an enlarging cyst compressing pelvic structures
Dyspareunia (deep)	Cyst compresses or displaces the pouch of Douglas → painful with deep penetration
Menstrual irregularity (oligomenorrhoea, amenorrhoea, or metrorrhagia)	Follicular cyst: excess oestrogen → suppresses FSH → anovulation → amenorrhoea followed by withdrawal bleed. Corpus luteal cyst: excess progesterone → maintains endometrium → delayed menses mimicking pregnancy. Thecoma/granulosa cell tumour: excess oestrogen → endometrial hyperplasia → irregular/heavy bleeding
Bloating / increased abdominal girth	Large cysts (especially mucinous cystadenomas) can fill the pelvis and abdomen. In malignancy: ascites contributes
Increasing abdominal girth with ascites	Suggestive of ovarian malignancy (especially in postmenopausal women) ^[1]^[3]
Urinary frequency / urgency	Anterior cyst compresses the bladder → reduced bladder capacity → increased urinary frequency
Constipation	Posterior cyst compresses the rectosigmoid colon → impaired transit
Back pain	Cyst compresses the lumbosacral nerve plexus or sacral hollow
Leg swelling / varicose veins	Large ovarian cysts can cause extramural venous obstruction → compresses pelvic veins (especially iliac veins) → impaired venous return → varicose veins, leg oedema ^[4]
Acute severe pelvic pain	Complication: Torsion (sudden twisting of ovarian pedicle → ischaemia), Rupture (cyst wall gives way → peritoneal irritation ± haemoperitoneum), Haemorrhage (into the cyst)
Virilisation (hirsutism, deepening voice, clitoromegaly)	Androgen-producing tumour (Sertoli-Leydig cell tumour) — rare
Symptoms of hyperthyroidism	Struma ovarii (teratoma with functioning thyroid tissue) — rare

Sign	Pathophysiological Basis
Pelvic/abdominal mass	The cyst itself. Arises from the pelvis → on bimanual examination, mass is felt separate from the uterus (unlike fibroids). On abdominal examination: lower abdominal mass, cannot get below it (arises from pelvis)
Mass characteristics: smooth, cystic, mobile, non-tender	Suggests benign cyst (smooth capsule, fluid content, free of adhesions)
Mass characteristics: irregular, fixed, hard, nodular	Raises suspicion for malignancy (infiltration of surrounding structures, solid components)
Mass is separate from the uterus on bimanual examination	Key distinguishing feature from uterine fibroids (which move with the cervix on bimanual)
Adnexal tenderness	Capsular stretching, haemorrhage, or torsion
Cervical motion tenderness (chandelier sign)	Torsion or ruptured cyst with peritoneal irritation; also PID/TOA
Ascites (shifting dullness, fluid thrill)	Malignancy → peritoneal carcinomatosis; or Meigs syndrome (fibroma + ascites + pleural effusion)
Pleural effusion (reduced breath sounds, dullness to percussion at right base)	Meigs syndrome (usually right-sided, because diaphragmatic lymphatics preferentially drain rightward)
Signs of oestrogen excess: endometrial thickening, breast tenderness	Oestrogen-secreting tumours (granulosa cell tumour, thecoma, large follicular cyst)
Signs of androgen excess: hirsutism, acne, male-pattern baldness	Androgen-secreting tumours (Sertoli-Leydig cell tumour)
Signs of peritonism (guarding, rebound tenderness, rigidity)	Complication: ruptured cyst (chemical or haemoperitoneum), torsion with necrosis, or ruptured TOA
Tachycardia, hypotension	Haemodynamic instability from significant haemoperitoneum (ruptured corpus luteal cyst) or sepsis (ruptured TOA)

Abdominal examination:

Inspect: distension, scars (previous laparoscopy/laparotomy)
Palpate: lower abdominal mass (cannot get below it = pelvic origin), tenderness, consistency (cystic vs solid), mobility, surface (smooth vs nodular)
Assess for ascites: shifting dullness, fluid thrill
Check for hepatomegaly (metastatic disease)

Bimanual pelvic examination:

Assess uterine size and mobility
Palpate adnexae: size, consistency, mobility, tenderness of the mass
Determine if the mass is separate from the uterus (ovarian) or moves with the cervix (uterine)
Assess the pouch of Douglas: fullness suggests ascites or mass

Speculum examination:

Assess cervix (rule out cervical pathology)
Any discharge, bleeding

Distinguishing Ovarian Cyst from Uterine Fibroid on Examination

Feature	Ovarian Cyst	Uterine Fibroid
Moves with cervix	No	Yes
Separate from uterus	Yes	No (arises from uterus)
Consistency	Cystic (fluctuant)	Firm/hard
Surface	Smooth	May be irregular (multiple fibroids)
Laterality	Usually lateral to uterus	Central (midline)

Endometriotic cysts are common in the Hong Kong population, correlating with global endometriosis prevalence (~10% of reproductive-age women). Local practice emphasises conservative management and fertility preservation given the city's already low birth rate.
Mature cystic teratomas are the most common benign ovarian neoplasm in Hong Kong, consistent with international data.
BRCA mutations — while overall prevalence is lower in East Asian populations compared to Ashkenazi Jewish populations, BRCA-associated ovarian cancer still accounts for ~15–20% of high-grade serous ovarian carcinomas in Hong Kong Chinese women. Genetic counselling and BRCA testing are increasingly offered at HKU/QMH for patients with high-grade serous ovarian cancer.
CA125: Can be elevated in benign conditions common in Hong Kong (e.g., endometriosis, pelvic inflammatory disease, hepatitis/liver cirrhosis) — leading to false positives. This must be interpreted in context.

High Yield Summary

Ovarian cysts range from physiological (functional) to neoplastic (benign and malignant). Classification: Functional, Inflammatory, Germ cell, Epithelial, Sex cord-stromal, Others ^[1].
Functional cysts (follicular, corpus luteal, theca lutein) are the most common and usually self-resolve. They arise from exaggerations of normal ovulatory physiology.
Endometriotic cysts ("chocolate cysts") are oestrogen-dependent, cyclically bleed, and do NOT resolve spontaneously. Small risk of clear cell / endometrioid carcinoma transformation.
Mature cystic teratoma (dermoid) is the most common benign ovarian neoplasm. Contains tissues from all three germ layers. Most common ovarian tumour to torse. AXR: tooth-shaped radiodensity; CT/MRI: diagnostic when fat demonstrated ^[3].
Mucinous cystadenomas can become enormous. Rupture → pseudomyxoma peritonei.
Meigs syndrome = fibroma + ascites + right pleural effusion (resolves with tumour removal).
RMI I = U × M × CA125. RMI ≥ 200 → CT + gynaecological oncology MDT referral ^[1].
Postmenopausal ovarian cyst algorithm: Measure CA125 → TVS + TAS → Calculate RMI → triage into low risk (conservative vs BSO) or high risk (staging laparotomy vs pelvic clearance) ^[1].
Key distinguishing feature from fibroid: ovarian mass is separate from the uterus on bimanual examination and does NOT move with the cervix.
Always perform β-hCG in reproductive-age women with pelvic pain + adnexal mass to rule out ectopic pregnancy.

Active Recall - Ovarian Cyst: Definition, Epidemiology, Aetiology, Classification, Clinical Features

^[1] Lecture slides: GC 118. Pelvic mass ovarian cancer and cysts; uterine fibroid; pelvic imaging.pdf (p35, p68) ^[2] Senior notes: Ryan Ho Endocrine.pdf (p77, p117 — PCOS and obesity associations) ^[3] Senior notes: Ryan Ho Radiology.pdf (p33 — imaging features of ovarian teratoma and simple cyst) ^[4] Senior notes: Maksim Surgery Notes.pdf (p172 — ovarian cysts as extramural cause of venous obstruction) ^[5] Senior notes: Maksim Medicine Notes.pdf (p79 — ovarian causes of amenorrhoea including PCOS) ^[6] Senior notes: Maksim Surgery Notes.pdf (p177 — ruptured ovarian cyst as cause of haemoperitoneum) ^[7] Senior notes: Ryan Ho Rheumatology.pdf (p167 — dermoid cyst pathogenesis)

Differential Diagnosis of Ovarian Cyst

The differential diagnosis (DDx) of an ovarian cyst is really two questions rolled into one:

When you find a "cyst" on the ovary: What type of ovarian cyst is it? (i.e., differentiating among the various ovarian cyst aetiologies discussed in the previous section — functional vs inflammatory vs neoplastic).
When a patient presents with a pelvic mass or acute pelvic pain: What else could mimic an ovarian cyst? (i.e., differentiating ovarian cyst from other pelvic pathology).

Both angles are essential for clinical practice and exams. The lecture slides emphasise that the most important part is the ability to formulate a list of differential diagnoses and to prioritise them according to the clinical condition ^[8].

The approach depends on the clinical scenario:

Presentation	Primary DDx Focus
Incidental pelvic mass on imaging	DDx of pelvic mass (gynaecological vs non-gynaecological)
Acute pelvic pain in a reproductive-age woman	Ovarian cyst complications vs ectopic pregnancy vs PID vs appendicitis
Chronic pelvic pain / mass symptoms	Ovarian cyst type, fibroid, endometriosis, malignancy
Postmenopausal pelvic mass	Ovarian malignancy until proven otherwise; benign cyst; uterine sarcoma

Golden Rule

Attend patients who need URGENT management first. Shock, severe pain (peritoneal signs) → may require straight laparotomy. Exclude ovarian cyst complications and pregnancy complications ^[1]. In any reproductive-age woman with acute pelvic pain, always exclude ectopic pregnancy (β-hCG) before anything else — it is life-threatening and treatable.

2. DDx of a Pelvic Mass (The Overarching Framework)

The lecture slides provide a clear framework, classifying by organ system of origin ^[1]:

Category	Examples	Key Distinguishing Clues
Uterine fibroid (leiomyoma)	Subserosal, pedunculated, intramural	Firm, moves with cervix on bimanual exam. Very vascular on Doppler ^[3]. Menorrhagia with clots. Most common pelvic tumour overall
Adenomyosis	Diffuse or focal	Uniformly enlarged "boggy" uterus, dysmenorrhoea, menorrhagia. Moves with cervix
Pregnancy	Undiagnosed pregnancy, molar pregnancy	Always check β-hCG! Teenage girls especially — don't forget about pregnancy ^[9]. Enlarged uterus, amenorrhoea, +β-hCG
Ovarian cyst	Functional, endometrioma, teratoma, cystadenoma	Separate from uterus, cystic, does NOT move with cervix
Paraovarian cyst	Arises from mesosalpinx (Wolffian duct remnants)	Located between tube and ovary, separate from both. Thin-walled, unilocular, cannot be distinguished from ovarian cyst clinically — diagnosis often made at surgery or on USS
Hydrosalpinx	Blocked, dilated fallopian tube filled with serous fluid	Tubular/sausage-shaped cystic structure on USS (the "cogwheel sign" on cross-section). History of PID. Associated infertility
Malignancies	Ovarian cancer, uterine sarcoma, metastatic disease	Irregular, solid/mixed, fixed, ascites, raised CA125, bilateral + suspicious → think Krukenberg tumour, metastasis from colon, stomach, breast ^[9]

Why is a paraovarian cyst important? It arises from Wolffian (mesonephric) duct remnants in the broad ligament. Unlike ovarian cysts, it does NOT arise from the ovary itself and therefore does NOT have the same malignant potential. However, clinically it is indistinguishable and the diagnosis is often only confirmed intraoperatively.

Category	Examples	Key Distinguishing Clues
Gastrointestinal	Mesenteric cyst, tumour (e.g. colorectal carcinoma), hernia, diverticulum (e.g. Meckel's), dilated bowel	GI symptoms (altered bowel habit, obstruction, per-rectal bleeding). CT abdomen differentiates. Mesenteric cyst: mobile perpendicular to mesentery root
Urological	Distended bladder, diverticulum, pelvic kidney, transplanted kidney	Check post-void residual / catheterise. Always exclude a full bladder before diagnosing a pelvic "mass." A pelvic kidney is incidental, non-tender, and visible on USS
Retroperitoneal	Sarcoma (usually not palpable)	Deep-seated, fixed, often large. Imaging (CT/MRI) essential. Rare
Others	Pseudocyst (related to previous surgeries), abscess	History of prior surgery (adhesions → loculated fluid = pseudocyst). Abscess: fever, raised inflammatory markers

Don't Forget the Non-Gynaecological Mimics

A distended bladder is one of the most embarrassing misdiagnoses of a pelvic mass. Always ask when the patient last voided and catheterise if in doubt. Similarly, a pelvic kidney can be mistaken for an adnexal mass on bimanual examination.

Torsion/haemorrhage of ovarian cyst, ectopic pregnancies, other early pregnancy complications and emergencies are the key gynaecological emergencies ^[8]. The DDx of acute lower abdominal/pelvic pain in a woman includes:

Diagnosis	Key Differentiating Features
Ruptured / haemorrhagic ovarian cyst	Sudden onset unilateral pelvic pain, often mid-cycle (follicular) or luteal phase (corpus luteal). USS: free fluid, cyst wall collapse. May cause haemoperitoneum ^[6]
Ovarian torsion	Sudden, severe, colicky pain ± nausea/vomiting (vagal response to twisting of the pedicle). Tender adnexal mass. USS with Doppler: absent/reduced ovarian blood flow ("whirlpool sign" of twisted pedicle). Dermoids are the most common tumour to torse
Ectopic pregnancy	Amenorrhoea + positive β-hCG + unilateral pelvic pain ± vaginal bleeding. Adnexal mass ± free fluid. Always the #1 rule-out in reproductive-age women — ruptured ectopic is life-threatening ^[6]^[10]
PID / tubo-ovarian abscess	Bilateral lower abdominal pain, fever, vaginal discharge, cervical motion tenderness. Risk factors: young age, multiple sexual partners, IUD. Elevated WCC/CRP
Appendicitis	RLQ pain (McBurney's point), anorexia, nausea, fever. Pain migrates from periumbilical → RLQ. In pelvic appendix, may mimic right ovarian pathology. Important DDx of RLQ pain in women ^[10]
"Mittelschmerz" pain	Ovulation pain — mid-cycle, brief (hours), unilateral, self-limiting. Due to follicular rupture and minor peritoneal irritation by follicular fluid. Diagnosis of exclusion ^[10]
Endometriosis	Cyclical pain (dysmenorrhoea), dyspareunia, dyschezia, infertility. Chronic rather than acute. Tender nodules in pouch of Douglas on PV exam
Ureteric colic	Severe colicky flank-to-groin pain, haematuria. No relationship to menstrual cycle. CT KUB diagnostic
UTI	Dysuria, frequency, suprapubic pain. Urine dipstick +ve for leucocytes/nitrites
Testicular torsion (male equivalent)	Listed in paediatric surgical DDx ^[10] — analogous emergency in males
DKA, acute MI, Addisonian crisis	Important medical DDx of acute abdomen ^[11]^[12]. Must be excluded, especially DKA in a young woman with T1DM

Once you've established that the mass is ovarian (separate from uterus on bimanual, confirmed on USS), the next step is to determine what kind of ovarian cyst. This is where ultrasound features, clinical context, and tumour markers guide you.

Cyst Type	Age	USS Appearance	Key Clinical Clues	Tumour Markers
Follicular cyst	Reproductive	Anechoic, avascular ^[3], thin-walled, unilocular, < 8 cm	Mid-cycle pain, resolves in 4–8 weeks	Normal CA125
Corpus luteal cyst	Reproductive	Thick wall ("ring of fire" on Doppler — peripheral vascularity), internal echoes (haemorrhagic), < 10 cm	Post-ovulation, delayed menses, mimics ectopic	Normal CA125, β-hCG –ve
Theca lutein cyst	Reproductive	Bilateral, multiple, large, multilocular	High β-hCG state (molar pregnancy, multiple pregnancy, OHSS)	Very high β-hCG
Endometrioma	Reproductive	"Ground glass" homogeneous low-level echoes, thick-walled, no internal vascularity	Dysmenorrhoea, dyspareunia, infertility	↑CA125 (mildly)
Mature teratoma	20–40 years	Variable depending on content ^[3]: fat-fluid level, dermoid plug (Rokitansky nodule), calcification	Often incidental. AXR: tooth-shaped radiodensity ^[3]	Normal CA125, raised AFP if immature
Serous cystadenoma	30–50 years	Thin-walled, unilocular, anechoic (like a big simple cyst)	Cannot distinguish from large follicular cyst on USS alone → persistent, does not resolve	Normal CA125
Mucinous cystadenoma	30–50 years	Very large, multilocular with thin septae, echogenic mucin	Can fill entire abdomen. Unilateral	Normal CA125
Ovarian fibroma	Postmenopausal	Solid, hypoechoic, well-circumscribed	Ascites + right pleural effusion (Meigs syndrome)	Normal CA125
Ovarian malignancy	Postmenopausal (peak)	Mixed solid-cystic, thick septae, papillary projections, vascularity within solid components, bilateral, ascites	Increasing abdominal girth, ascites, weight loss	↑↑CA125 (typically > 200 U/mL)

Exam Scenario: F/75 with increasing abdominal girth, pelvic mass, ascites, mixed solid-cystic on USS, uterus cannot be visualised

This is a classic exam question ^[3]. The answer is ovarian cancer — NOT a functional cyst (postmenopausal women don't ovulate, so functional cysts are very rare), NOT a dermoid (these are typically reproductive-age), NOT a fibroma (which is solid, not mixed). The inability to visualise the uterus suggests the mass has engulfed/replaced the ovary and obscured the uterus. Ascites with mixed solid-cystic features in a postmenopausal woman = malignancy until proven otherwise.

5. DDx by Clinical Presentation — Special Scenarios

Don't forget pregnancy ^[9] — even if the patient denies sexual activity. Always do a β-hCG.
Functional cysts are common after menarche as the HPO axis matures (irregular ovulation).
Mature teratoma — most common ovarian neoplasm in this age group.
Malignant germ cell tumours (dysgerminoma, immature teratoma, yolk sac tumour) — rare but important; check AFP, β-hCG, LDH.

Management approach from lecture slides ^[1]:

Asymptomatic: can observe and repeat ultrasound (3–6 months)
Symptomatic: possible complications, needs removal
Persistent cyst: consider removal to confirm diagnosis (cystectomy vs salpingo-oophorectomy; laparoscopy vs laparotomy)
Suspected cancer: refer oncology, exclude secondary from colon, stomach, breast etc, staging surgery ± chemotherapy

Higher index of suspicion for malignancy — postmenopausal ovaries are normally small and quiescent.
Use RMI to triage ^[1] (detailed in previous section).
If bilateral and suspicious-looking → think Krukenberg tumour (metastatic signet-ring cell carcinoma, usually from gastric or colonic primary) ^[9].

Per the surgery notes, ovarian cyst and its complications feature prominently in the DDx of acute abdomen ^[10]^[11]^[12]:

RLQ pain DDx: appendicitis, caecal diverticulitis, Crohn's disease, Meckel's diverticulitis, Mittelschmerz, ovarian cyst complications, PID, ruptured ectopic pregnancy ^[10]
Life-threatening DDx of acute abdomen: includes ruptured ectopic pregnancy ^[11] — always the top priority to exclude
Paediatric acute abdomen (female): ectopic pregnancy / ovarian cyst torsion / PID ^[12]
Haemoperitoneum: ruptured ovarian cyst and ruptured ectopic pregnancy are key pelvic causes ^[6]

Step	What it tells you	Key action
β-hCG	Excludes pregnancy and ectopic	FIRST investigation in any reproductive-age woman with pelvic pain/mass
Pelvic USS (TVS + TAS)	Characterises the mass (simple vs complex, solid vs cystic, vascularity, septae, laterality)	First-line imaging for any pelvic mass ^[1]
CA125	Elevated in epithelial ovarian cancer, endometriosis, PID, TB, liver cirrhosis, menstruation — not specific	Calculate RMI in postmenopausal women ^[1]
AFP, β-hCG, LDH	Germ cell tumour markers (yolk sac tumour, dysgerminoma, choriocarcinoma)	Young women with solid/complex ovarian mass
Inhibin	Granulosa cell tumour marker	Postmenopausal woman with oestrogen excess symptoms
CT abdomen + pelvis	Staging if malignancy suspected; also differentiates GI/urological causes	RMI ≥ 200 → CT scan ^[1]
MRI pelvis	Better soft tissue characterisation; useful for endometrioma vs malignancy	Second-line when USS is indeterminate
Doppler USS	Vascularity within mass; absent flow in torsion	Whirlpool sign (torsion), ring of fire (corpus luteal cyst)

Uterine fibroid, ovarian mass and cancer are important differential diagnoses of pelvic mass. History and physical examination usually help to suggest a diagnosis. Pelvic ultrasound is commonly performed. Management will depend on the age, symptom, condition and wish of the patient ^[1].

Diagnosis	Moves with cervix?	Consistency	USS	β-hCG	CA125	Special Features
Uterine fibroid	Yes	Firm	Solid, vascular	–ve	Normal/mildly ↑	Menorrhagia, firm enlarged uterus
Ovarian cyst (functional)	No	Cystic	Anechoic, thin-walled	–ve	Normal	Self-resolves in 4–8 weeks
Ectopic pregnancy	No	Tender, adnexal	Adnexal mass ± free fluid, empty uterus	+ve	N/A	Amenorrhoea, vaginal spotting
Endometrioma	No	Cystic, tender	Ground glass echoes	–ve	Mildly ↑	Cyclical pain, infertility
Ovarian malignancy	No	Solid/mixed, fixed	Complex, solid, papillary, ascites	–ve	↑↑	Postmenopausal, weight loss, ascites
PID/TOA	No	Tender, boggy	Tubo-ovarian complex, abscess	–ve	May be ↑	Fever, discharge, cervical motion tenderness
Appendicitis	N/A	RLQ tenderness	Target sign, periappendiceal fluid	–ve	Normal	Migration of pain, anorexia, Rovsing's sign
Distended bladder	No	Smooth, midline	Full bladder	–ve	Normal	Disappears after catheterisation

High Yield Summary

DDx of pelvic mass: Gynaecological (fibroid, pregnancy, ovarian cyst, paraovarian cyst, hydrosalpinx, malignancies) vs Non-gynaecological (GI: mesenteric cyst, tumour; Urological: distended bladder, pelvic kidney; Retroperitoneal: sarcoma; Others: pseudocyst, abscess) ^[1].
Always exclude pregnancy first (β-hCG) — especially in teenage girls ^[8]^[9].
In the acute setting: exclude ovarian cyst complications and pregnancy complications first. Shock or peritoneal signs → may need straight laparotomy ^[1].
Premenopausal adnexal mass: Asymptomatic → observe with repeat USS in 3–6 months. Symptomatic → consider removal. Persistent → cystectomy vs salpingo-oophorectomy. Suspected cancer → oncology referral, exclude secondaries from colon, stomach, breast ^[1].
Postmenopausal adnexal mass: always calculate RMI. RMI ≥ 200 → CT + gynaecological oncology MDT ^[1].
Bilateral, suspicious adnexal masses → think Krukenberg tumour (metastatic from GI or breast primary) ^[9].
Key examination distinction: ovarian cyst is separate from uterus and does NOT move with cervix; fibroid moves with cervix.
The RLQ pain DDx in women must include Mittelschmerz, ovarian cyst complications, PID, and ruptured ectopic pregnancy alongside appendicitis ^[10].

Active Recall - Differential Diagnosis of Ovarian Cyst

References

^[1] Lecture slides: GC 118. Pelvic mass ovarian cancer and cysts; uterine fibroid; pelvic imaging.pdf (p23, p24, p66, p68, p71) ^[3] Senior notes: Ryan Ho Radiology.pdf (p33, p39 — USS features of ovarian cyst and exam question on F/75 with ovarian cancer) ^[6] Senior notes: Maksim Surgery Notes.pdf (p177 — ruptured ovarian cyst as cause of haemoperitoneum) ^[8] Lecture slides: Block C - Gyanecological Emergency Notes to Students.pdf (p1 — DDx prioritisation, gynaecological emergencies) ^[9] Lecture slides: Block C - Pelvic mass_ ovarian cancer and cysts; uterine fibroid; pelvic imaging.pdf (p16, p17, p28, p59) ^[10] Senior notes: Maksim Surgery Notes.pdf (p89 — DDx of RLQ pain including Mittelschmerz, ovarian cyst, PID, ectopic) ^[11] Senior notes: Maksim Surgery Notes.pdf (p45 — life-threatening DDx of acute abdomen) ^[12] Senior notes: Maksim Surgery Notes.pdf (p336 — paediatric surgical abdomen DDx including ovarian cyst torsion)

Diagnosis of Ovarian Cyst

Unlike conditions such as rheumatoid arthritis or diabetes, ovarian cysts do not have formal "diagnostic criteria" per se (there is no equivalent of the ACR criteria or WHO diagnostic thresholds). Instead, the diagnosis is established by:

Clinical suspicion — history and examination (covered in previous sections)
Imaging confirmation — pelvic ultrasound is the cornerstone
Characterisation — determining the type of cyst (functional vs neoplastic vs inflammatory) and, critically, whether it is benign or malignant
Tumour markers — to risk-stratify, not to diagnose in isolation

The diagnostic challenge is not "does she have an ovarian cyst?" (USS answers that immediately) but rather "what kind of ovarian cyst is it, and is it safe to leave alone?" This is the clinical question that drives the entire algorithm.

Before any imaging, the clinical approach begins at the bedside:

Step	Purpose	Key Points
Vital signs	Vital signs if in pain ^[1] — haemodynamic instability suggests rupture/torsion/ectopic	Tachycardia, hypotension → haemoperitoneum or sepsis
Pregnancy test (β-hCG)	First and most important investigation in any reproductive-age woman ^[13]^[14]	Must exclude ectopic pregnancy before proceeding. A positive β-hCG completely changes the differential
Pain assessment	Acute vs chronic, unilateral vs bilateral, relation to menstrual cycle	Sudden onset + severe → torsion or rupture; cyclical → endometrioma; mid-cycle → Mittelschmerz or follicular cyst
Menstrual history	Last menstrual period, regularity, intermenstrual/postmenopausal bleeding	Amenorrhoea → pregnancy or corpus luteal cyst; postmenopausal bleeding with adnexal mass → malignancy
Bimanual examination	Mass separate from uterus, mobility (dermoid cyst → usually mobile; endometriotic cyst → not mobile due to surrounding inflammation) ^[9], consistency, tenderness, peritoneal signs ^[1]	Usually separated from uterus; less mobile if adhesions, endometriosis. Usually no ascites (ascites → more neoplastic cause) ^[1]^[9]

Key Examination Pointers from Lecture

Ovarian cysts tend not to cause ascites → ascites would indicate a more neoplastic cause ^[9]. Dermoid cysts are usually mobile; endometriotic cysts are not mobile due to surrounding inflammation ^[9]. May not be palpable if small or soft ^[1]. Special situations: complications, Meigs syndrome ^[1].

3. Investigation Modalities

Investigation	Why	Key Findings and Interpretation
β-hCG (serum/urine)	Exclude pregnancy/ectopic pregnancy — the #1 life-threatening mimic ^[13]^[14]	Positive → pregnancy-related pathology (ectopic, miscarriage, molar pregnancy, theca lutein cyst). Negative → proceed with non-pregnancy workup
CBC (FBC)	Infection (↑WCC), haemorrhage (↓Hb), chronicity	↑WCC → PID/TOA, torsion with necrosis. ↓Hb → ruptured haemorrhagic cyst. Left shift → acute inflammation
CRP / ESR	Inflammation	Elevated → PID/TOA, torsion. Normal in simple functional cysts
CA125	Ovarian cancer risk assessment ^[1]	See detailed interpretation below. Not diagnostic alone — elevated in many benign conditions
AFP (alpha-fetoprotein)	Germ cell tumour markers	↑AFP → yolk sac tumour (endodermal sinus tumour), or immature teratoma
β-hCG (as tumour marker)	Germ cell tumour marker	↑β-hCG → choriocarcinoma, dysgerminoma (10%), embryonal carcinoma
LDH	Germ cell tumour marker	↑LDH → dysgerminoma (most common malignant germ cell tumour)
Inhibin A and B	Sex cord-stromal tumour marker	↑Inhibin → granulosa cell tumour
Oestradiol	Functional status	↑ → oestrogen-secreting tumour (granulosa cell, thecoma) causing endometrial hyperplasia
Testosterone / DHEAS	Androgen excess	↑ → Sertoli-Leydig cell tumour, or PCOS
Serum mid-luteal progesterone	Ovulation confirmation (in infertility workup context) ^[15]	Measured a week before next expected period — level > 30 nmol/L confirms ovulation
FSH, prolactin, thyroxine	Irregular cycles workup ^[15]	↑FSH → premature ovarian insufficiency; ↑prolactin → hyperprolactinaemia; abnormal TFTs → thyroid disease
RFT, LFT	Pre-operative baseline; also important because CA125 can be elevated in liver cirrhosis and renal failure	Elevated LFTs → hepatic cause of ↑CA125 (false positive)
Clotting profile, group & save	Pre-operative, especially if haemorrhagic cyst or planned surgery	Essential if surgery anticipated

CA125 — Detailed Interpretation

CA125 (Cancer Antigen 125) is a glycoprotein expressed by coelomic epithelium (peritoneum, pleura, pericardium) and Müllerian duct derivatives (endocervix, endometrium, fallopian tube). Understanding its origin explains why it is elevated in so many conditions:

Condition	CA125 Level	Explanation
Epithelial ovarian cancer (especially serous)	Markedly ↑↑ (often > 200 U/mL)	Tumour cells express CA125 abundantly
Endometriosis	Mildly ↑ (35–200)	Ectopic endometrial tissue expresses CA125
PID	Mildly ↑	Peritoneal inflammation
Menstruation	Mildly ↑	Endometrial shedding releases CA125
Pregnancy (1st trimester)	Mildly ↑	Decidualised endometrium
Liver cirrhosis / ascites	↑	Peritoneal irritation; impaired hepatic clearance
Peritoneal TB	↑	Granulomatous peritoneal inflammation
Uterine fibroids	Normal or mildly ↑	Myometrial stretching

Exam Pearl

CA125 has poor specificity in premenopausal women because of the many benign causes of elevation listed above. It is most useful in postmenopausal women where the background "noise" is lower, and as part of the RMI calculation ^[1]. Never diagnose ovarian cancer on CA125 alone.

3.2 Imaging Investigations

Pelvic ultrasound is commonly performed ^[1] and is the gold standard first-line imaging for any pelvic mass. It is non-invasive, widely available, no radiation, and provides excellent pelvic soft tissue characterisation.

TVS (Transvaginal Scanning): Higher frequency probe placed in the vaginal fornix → closer to the ovaries and uterus → superior resolution for characterising adnexal masses. The go-to approach.
TAS (Transabdominal Scanning): Lower frequency probe on the anterior abdominal wall → wider field of view, better for large masses that extend beyond the pelvis. Requires a full bladder as an acoustic window.
Both TVS + TAS should be performed together for comprehensive evaluation ^[1].

Systematic USS Reporting of an Adnexal Mass ^[9]:

What to report for an adnexal mass on ultrasound: ^[9]

Feature	What to Document	Significance
Side	Unilateral vs bilateral	Bilateral + suspicious → think Krukenberg tumour, metastasis ^[9]
Size	Maximum diameter in 3 planes	> 5 cm more likely neoplastic; > 7 cm → consider CT
Morphology	Cystic, solid, or mixed	Purely cystic → likely benign; solid/mixed → higher malignancy risk
Wall	Thin vs thick, smooth vs irregular	Thin + smooth = benign; thick + irregular = suspicious
Septae	Absent (unilocular), thin septae, thick septae	Thin septae = likely benign; thick septae (> 3 mm) = suspicious
Internal content	Anechoic, low-level echoes, debris, fat, calcification	Anechoic = simple cyst; ground glass = endometrioma; echogenic = dermoid/haemorrhagic
Papillary projections	Present/absent, number, height	Papillary projections = strong indicator of malignancy
Vascularity (Doppler)	No flow, peripheral flow, central flow, septal flow	A little Doppler flow is expected and normal → too much is abnormal ^[9]. Central/septal vascularity = suspicious
Free fluid	Absent, small amount, large amount	A little fluid in the peritoneal cavity is acceptable → too much is abnormal ^[9]. Large ascites = malignancy or rupture
Associated findings	Uterus, other adnexa, lymphadenopathy	Look at uterus first to orient yourself ^[9]. For postmenopausal women, atrophic ovaries are difficult to locate ^[9]

Cyst Type	USS Appearance
Simple cyst (functional)	Anechoic, avascular ^[3], thin-walled, well-defined, posterior acoustic enhancement. Unilocular
Corpus luteal cyst	Thick echogenic wall, "ring of fire" on colour Doppler (intense peripheral vascularity due to luteinised wall), internal echoes (haemorrhagic content), lace-like reticular pattern
Endometrioma	Homogeneous low-level internal echoes ("ground glass"), thick wall, no internal vascularity, may have wall nodularity
Mature teratoma (dermoid)	Variable appearance depending on content ^[3] — dermoid plug (Rokitansky nodule = mural echogenic nodule), fat-fluid level, "tip of the iceberg" sign (strong anterior echoes with posterior shadowing from hair/sebum), calcification
Serous cystadenoma	Thin-walled, unilocular, anechoic — indistinguishable from large simple cyst on USS
Mucinous cystadenoma	Large, multiloculated ("honeycomb" pattern), thin internal septae, variable echogenicity of locules (different mucin concentrations)
Ovarian fibroma	Solid, well-circumscribed, hypoechoic, ± posterior acoustic shadowing
Ovarian malignancy	Complex: mixed solid-cystic, thick septae (> 3 mm), papillary projections, solid components with vascularity, bilateral, ascites

Not routinely performed for ovarian cysts, but can provide incidental clues:

AXR: tooth-shaped radiodensity in the pelvis → ovarian teratoma ^[3]
Calcification patterns (teeth, bone fragments) are pathognomonic for mature teratoma

CT scan is indicated when RMI ≥ 200 ^[1] or when malignancy is suspected. It serves multiple roles:

Role	Details
Characterisation	Definitive diagnosis for teratoma, especially when fat content is demonstrated ^[3] (fat has distinctive negative Hounsfield units on CT: -50 to -100 HU)
Staging	Evaluates peritoneal disease, lymphadenopathy (para-aortic, pelvic), omental cake, liver/lung metastases
Surgical planning	Delineates anatomical relationships, assesses operability
Exclude non-gynaecological pathology	Appendicitis, diverticulitis, urological pathology, mesenteric masses

CT interpretation principles for ovarian masses ^[13]:

CT Feature	Significance
Well-defined, round/oval	Slow, displacing growth → likely benign
Irregular, infiltrative	Malignancy
Fat density (-50 to -100 HU)	Teratoma (dermoid)
Calcification within cystic mass	Teratoma (teeth, bone)
Omental caking	Peritoneal carcinomatosis (ovarian cancer)
Ascites + peritoneal nodularity	Stage III/IV ovarian malignancy

Second-line imaging, used when USS is indeterminate. Superior soft tissue contrast compared to CT.

Indication	MRI Advantage
Indeterminate adnexal mass on USS	T1W fat-sat sequences differentiate fat (teratoma) from blood (endometrioma) — both appear bright on T1W, but fat suppresses with fat-sat while blood does not
Endometrioma vs haemorrhagic cyst	T1W bright + T2W dark ("shading") = endometrioma (old blood with high protein/haemosiderin). Haemorrhagic cyst: T1W bright + T2W bright (acute blood)
Characterising solid components	Better than USS for determining if solid component is truly solid or just debris
Teratoma	Definitive diagnosis when fat content demonstrated ^[3] — chemical shift artifact at fat-water interface

O-RADS is the standardised ultrasound classification system for adnexal masses (analogous to BI-RADS for breast). It assigns risk categories based on USS features:

O-RADS Score	Category	Management
0	Incomplete evaluation	Needs further imaging
1	Normal ovary / physiologic finding	No follow-up needed
2	Almost certainly benign (< 1% malignancy risk)	Follow-up USS
3	Low risk of malignancy (1–10%)	Follow-up USS or MRI
4	Intermediate risk (10–50%)	Referral to gynaecological oncology
5	High risk of malignancy (> 50%)	Referral to gynaecological oncology

4. Diagnostic Algorithm

The overall diagnostic approach differs based on menopausal status — this is the most important branching point because the pretest probability of malignancy is fundamentally different.

Key management points for premenopausal adnexal mass: ^[1]

Asymptomatic: can observe and repeat ultrasound (3–6 months)
Symptomatic: possible complications, needs removal
Persistent cyst: consider removal to confirm diagnosis (cystectomy vs salpingo-oophorectomy; laparoscopy vs laparotomy)
Suspected cancer: refer oncology, exclude secondary from colon, stomach, breast etc, staging surgery ± chemotherapy

This is the key algorithm from the lecture slides and must be known in detail:

RMI I = U × M × CA125 ^[1]

Component	Scoring
Ultrasound score (U)	0 features = 0; 1 feature = 1; ≥ 2 features = 3. USS features: multilocular, solid areas, bilateral, ascites, metastases
Menopausal status (M)	Premenopausal = 1; Postmenopausal = 3
CA125	Absolute value in U/mL

Example calculation: A 65-year-old postmenopausal woman (M = 3) with a bilateral ovarian mass with solid areas (2 USS features → U = 3) and CA125 = 150 U/mL → RMI I = 3 × 3 × 150 = 1350 → well above 200 → CT + oncology MDT referral.

Why RMI I ≥ 200 is the threshold

At this threshold, the sensitivity for detecting ovarian malignancy is approximately 78% and specificity is approximately 87%. It provides a pragmatic balance between catching cancers early and avoiding unnecessary surgical intervention in benign cases. The postmenopausal menopausal multiplier of 3 (vs 1 for premenopausal) reflects the inherently higher pretest probability of malignancy in postmenopausal women.

Clinical Scenario	Investigation of Choice	Rationale
Any reproductive-age woman with pelvic pain/mass	β-hCG first	Exclude ectopic pregnancy — life-threatening
Initial characterisation of any pelvic mass	TVS + TAS ^[1]	First-line, non-invasive, excellent resolution
PV detected left adnexal mass with urinary incontinence	Transvaginal USS ^[3]	Best for characterising adnexal pathology (transvaginal > transabdominal for adnexal detail)
Postmenopausal ovarian cyst	CA125 + TVS + TAS → calculate RMI ^[1]	Risk stratification for malignancy
Suspected malignancy / RMI ≥ 200	CT abdomen and pelvis ^[1]	Staging and surgical planning
Indeterminate mass on USS	MRI pelvis	Superior soft tissue characterisation
Suspected dermoid (teratoma)	CT or MRI — definitive when fat demonstrated ^[3]	Fat has distinctive density/signal
Infertility workup — confirm tubal patency	Hysterosalpingogram (HSG) ^[3]	Radio-opaque dye instilled into uterus → tubal spill confirms patency
Suspected torsion	USS with Doppler	Absent/reduced ovarian blood flow; "whirlpool sign" of twisted pedicle
Young woman with solid ovarian mass	AFP, β-hCG, LDH, inhibin	Germ cell and sex cord-stromal tumour markers

Exam Question Pattern

A past exam question ^[3] asks: "PV detected left adnexal mass with urinary incontinence — which investigation is most appropriate?" The answer is transvaginal USS (not transabdominal, not AXR, not HSG). TVS provides the best resolution for characterising adnexal pathology. The urinary incontinence is likely caused by mass effect on the bladder — TVS will characterise the mass AND assess its relationship to the bladder.

Definitive diagnosis of an ovarian cyst's histological type requires tissue sampling — but this is almost never done via percutaneous biopsy (risk of tumour seeding/spillage if malignant). Instead:

Surgical excision (cystectomy or oophorectomy) → specimen sent for histopathology
Intraoperative frozen section — rapid histological assessment during surgery to guide the extent of the procedure (e.g., if frozen section shows malignancy → proceed to full staging; if benign → stop at cystectomy)
Fine-needle aspiration (FNA) of ovarian cysts is generally NOT recommended because:
1. Cannot distinguish benign from malignant on cytology alone (needs architecture)
2. Risk of cyst rupture and peritoneal spillage → upstaging if malignant
3. High recurrence rate after aspiration alone

Important Principle

Do NOT aspirate an ovarian cyst to diagnose it. The definitive diagnosis comes from surgical excision and histopathology. Aspiration risks tumour spillage (if malignant) and has a high recurrence rate. The exception is in very selected cases of clearly simple cysts in high-surgical-risk patients, but this is rare.

High Yield Summary

β-hCG is the first investigation in any reproductive-age woman with a pelvic mass or pelvic pain — to exclude ectopic pregnancy.
Pelvic USS (TVS + TAS) is the first-line imaging for all pelvic masses ^[1]. TVS provides superior resolution for adnexal characterisation.
Systematic USS reporting includes: side, size, morphology, wall, septae, content, papillary projections, vascularity, free fluid, and associated findings ^[9]. O-RADS classifies risk ^[9].
Simple cyst on USS: anechoic, avascular, thin-walled ^[3] — almost always benign; observe if small and asymptomatic.
CA125 is useful in postmenopausal women as part of RMI calculation ^[1], but has poor specificity in premenopausal women (elevated in endometriosis, PID, menstruation, liver disease).
RMI I = U × M × CA125. RMI ≥ 200 → CT abdomen/pelvis + gynaecological oncology MDT referral ^[1].
CT/MRI: definitive for teratoma when fat content is demonstrated ^[3]. CT is for staging when malignancy suspected.
Definitive diagnosis = surgical excision + histopathology. Do NOT aspirate ovarian cysts for diagnosis (risk of spillage and recurrence).
Premenopausal: asymptomatic → observe with USS in 3–6 months; symptomatic → remove; persistent → cystectomy vs oophorectomy; suspected cancer → oncology referral ^[1].
Postmenopausal: low-risk RMI with simple features → conservative; low-risk with non-simple features → BSO; high-risk → staging laparotomy ^[1].

Active Recall - Diagnosis of Ovarian Cyst

References

^[1] Lecture slides: GC 118. Pelvic mass ovarian cancer and cysts; uterine fibroid; pelvic imaging.pdf (p20, p21, p66, p68) ^[3] Senior notes: Ryan Ho Radiology.pdf (p33, p39, p40 — USS features, AXR findings, exam questions) ^[9] Lecture slides: Block C - Pelvic mass_ ovarian cancer and cysts; uterine fibroid; pelvic imaging.pdf (p15, p16, p18, p28, p30) ^[13] Senior notes: Ryan Ho Diagnostic Radiology.pdf (p39 — CT interpretation principles) ^[14] Senior notes: Ryan Ho Fundamentals.pdf (p279 — initial workup of acute abdomen including pregnancy test) ^[15] Lecture slides: GC 117. I want to have a baby male and female infertility.pdf (p24 — ovulation investigations)

Management of Ovarian Cyst

The management of an ovarian cyst is driven by four key factors, which you should always consider systematically:

Age / menopausal status — premenopausal women have a much lower pretest probability of malignancy and require fertility preservation; postmenopausal women have a higher malignancy risk and often do not need fertility preservation.
Symptoms — asymptomatic cysts can often be observed; symptomatic cysts (pain, pressure, complications) need intervention.
Ultrasound morphology — simple vs complex features determine the likelihood of malignancy.
The wish of the patient ^[1] — always factor in patient preference regarding fertility, surgery, and conservative management.

Management will depend on the age, symptom, condition and wish of the patient ^[1].

The overarching philosophy is: observe what is likely benign and functional; operate on what is persistent, symptomatic, or suspicious for malignancy.

3. Management by Clinical Scenario

Some indications require emergency management — ovarian cyst complications, pregnancy complications ^[9].

Emergency	Management	Rationale
Ovarian torsion	Emergency laparoscopy → detorsion (untwist the pedicle). If ovary viable → conserve (cystectomy + detorsion). If ovary necrotic/gangrenous → salpingo-oophorectomy	Time-sensitive — ovarian viability depends on duration of torsion. Within 6–8 hours, detorsion can salvage the ovary. Beyond that, risk of necrosis increases. Always attempt detorsion first, even if the ovary looks dusky (it often recovers)
Ruptured cyst with haemodynamic instability	Resuscitation (IV fluids, crossmatch blood) → emergency laparoscopy/laparotomy → haemostasis (cautery, suturing, oophorectomy if bleeding uncontrollable)	Haemoperitoneum from ruptured corpus luteal cyst can be massive. Haemodynamically stable patients with small amounts of free fluid can be managed conservatively (analgesia, monitoring)
Ruptured ectopic pregnancy	Emergency laparotomy/laparoscopy → salpingectomy (or salpingotomy if contralateral tube absent/damaged)	Life-threatening haemoperitoneum. Must be excluded before any ovarian cyst can be managed conservatively
Ruptured tubo-ovarian abscess	IV antibiotics (broad-spectrum: cephalosporin + metronidazole + doxycycline) + emergency drainage (percutaneous or surgical)	Peritonitis and sepsis risk. Antibiotics alone may be insufficient if frank rupture has occurred

Torsion — Detorse First, Think Later

The historical teaching was to remove a torsed ovary without untwisting it (fear of releasing thrombotic emboli). This is outdated. Current practice is to detorse regardless of the ovary's appearance — studies have shown that embolisation risk is negligible and ovarian salvage rates are significantly improved with detorsion. Even a dusky, oedematous ovary often recovers full function after untwisting.

3.2 Premenopausal Adnexal Mass / Cyst [1]

The guiding principle in premenopausal women is fertility preservation — be as conservative as possible unless malignancy is suspected.

Asymptomatic: can observe and repeat ultrasound (3–6 months) ^[1]
Indication: Simple, unilocular, < 5 cm, anechoic cyst → overwhelmingly likely to be a functional cyst (follicular or corpus luteal)
Protocol: Repeat USS in 6–12 weeks (at least one menstrual cycle later)
- If resolved → confirms functional cyst → discharge
- If persistent → unlikely to be functional → consider removal
Rationale: Functional cysts resolve spontaneously as hormonal support wanes. Operating on them is unnecessary and exposes the patient to surgical risk. However, neoplastic cysts do NOT resolve, so persistence mandates further action.

Symptomatic: possible complications, needs removal ^[1]
Indications for surgery:
- Pain not controlled with analgesia
- Complications (torsion, rupture, haemorrhage)
- Large size (> 5–7 cm) causing mass effect
- Rapidly enlarging cyst

Persistent cyst: consider removal to confirm diagnosis ^[1]
A cyst that persists beyond 2–3 menstrual cycles is unlikely to be functional and needs histological diagnosis
Cystectomy vs salpingo-oophorectomy: ^[1]
- Cystectomy (remove cyst, preserve ovary) — preferred in young women to preserve fertility. Suitable for benign-appearing cysts (dermoid, endometrioma, cystadenoma)
- Salpingo-oophorectomy (remove entire ovary + tube) — indicated if the cyst has destroyed the ovary, if the patient has completed childbearing, or if malignancy cannot be excluded
Laparoscopy vs laparotomy: ^[1]
- Laparoscopy — preferred approach for most benign cysts. Advantages: less pain, shorter recovery, smaller scars, better cosmesis
- Laparotomy — indicated if the cyst is very large (difficult to extract laparoscopically), if malignancy is suspected (need intact specimen without spillage for staging), or if adhesions from prior surgery make laparoscopy unsafe

Feature	Cystectomy	Salpingo-oophorectomy
Preserves ovary	Yes	No
Fertility preservation	Yes	Depends (if contralateral ovary intact)
Risk of recurrence	Higher (residual tissue)	Lower
Best for	Young women, benign-appearing cysts	Completed family, suspicious cysts, destroyed ovary

Suspected cancer: refer oncology, exclude secondary from colon, stomach, breast etc, staging surgery ± chemotherapy ^[1]
Key point: Do NOT perform a simple cystectomy/oophorectomy if malignancy is suspected — this can compromise staging and prognosis
Refer to gynaecological oncology for proper staging surgery

Cyst Type	Management	Rationale
Follicular cyst	Observe → resolves in 4–8 weeks. COC pills do NOT hasten resolution (common misconception), but can prevent new functional cysts	Self-limiting; granulosa cell lining involutes as FSH/LH support wanes
Corpus luteal cyst	Observe if stable. If ruptured with haemodynamic instability → surgical haemostasis	Often haemorrhagic; most reabsorb spontaneously
Theca lutein cyst	Treat underlying cause (evacuate mole, reduce gonadotropin dose). Cysts resolve once hCG stimulus removed	Driven by hCG — removing the stimulus → cyst regression
Endometrioma	Medical: hormonal suppression (COC pills, progestogens, GnRH agonists) → reduces size and symptoms but does not cure. Surgical: laparoscopic excision (cystectomy) for cysts > 3–4 cm, especially if infertility or refractory symptoms	Does NOT resolve spontaneously. Excision preferred over drainage (drainage has ~80% recurrence). Post-op hormonal therapy reduces recurrence
Mature teratoma (dermoid)	Surgical excision (cystectomy, laparoscopic). Careful intraoperative handling to avoid spillage (sebaceous content causes chemical peritonitis)	Does NOT resolve spontaneously. Risk of torsion (most common tumour to torse) — prophylactic removal often recommended even if asymptomatic, especially if > 5 cm
Serous/mucinous cystadenoma	Surgical excision (cystectomy or oophorectomy). Must send for histology to exclude borderline/malignant component	Neoplastic — will not resolve. Need histological diagnosis

Do Oral Contraceptive Pills Treat Ovarian Cysts?

A common misconception. COC pills do NOT accelerate the resolution of existing functional cysts. Randomised controlled trials have shown no difference in resolution rates. However, COC pills do prevent the formation of new functional cysts by suppressing ovulation (no follicle development → no follicular cyst; no ovulation → no corpus luteum). So they have a role in prevention, not treatment.

3.4 Postmenopausal Ovarian Cyst [1]

The management of postmenopausal ovarian cysts follows the RCOG algorithm ^[9] based on the RMI score:

Step 1: Measure CA125 + TVS + TAS [1]

Step 2: Calculate RMI I = U × M × CA125 [1]

5 criteria to determine whether conservative management is possible ^[9]:

Cysts fulfilling ALL of the following → consider conservative management: ^[1]
1. Asymptomatic
2. Simple cyst
3. < 5 cm
4. Unilocular
5. Unilateral
→ Repeat assessment with CA125, TVS + TAS at intervals (typically 4–6 monthly for at least 1 year) ^[1]
Cysts with ANY of the following → MDT review → consider laparoscopic BSO (usually bilateral): ^[1]
1. Symptomatic
2. Non-simple features
3. > 5 cm
4. Multilocular
5. Bilateral

For postmenopausal women, can be more radical with operation ^[9] — because fertility is no longer a concern and the risk of malignancy is higher, bilateral salpingo-oophorectomy is the standard surgical approach rather than cystectomy.

CT scan (abdomen and pelvis) ^[1]
Referral for gynaecological oncology MDT review ^[1]
MDT determines likelihood of malignancy:

Likelihood	Surgical Approach	By Whom
High likelihood of ovarian malignancy	Laparotomy: full staging procedure (TAH + BSO + pelvic/para-aortic lymph node sampling + omentectomy + peritoneal biopsies + peritoneal cytology + appendicectomy if mucinous)	By a trained gynaecological oncologist ^[1]
Low likelihood of ovarian malignancy	Laparotomy: pelvic clearance (TAH + BSO + omentectomy + peritoneal cytology)	By a suitably trained gynaecologist ^[1]

Why Full Staging at Laparotomy?

Staging at initial surgery is critical because:

Prognosis depends on stage — stage I ovarian cancer has > 90% 5-year survival vs < 30% for stage IV.
Adjuvant chemotherapy decisions depend on accurate staging — unstaged/incompletely staged patients may receive unnecessary chemotherapy or, worse, miss necessary treatment.
Re-staging surgery (if initial surgery was inadequate) adds morbidity and delays treatment. This is why suspected malignancy should be referred to a gynaecological oncologist — they perform the full staging in one operation.

Management is complicated, depends on many factors ^[9]:

Scenario	Approach
Operable disease	Operate first — time-sensitive operation, therapeutic and diagnostic ^[9]. Primary debulking surgery (PDS) → aim for complete cytoreduction (no residual disease) → adjuvant chemotherapy (carboplatin + paclitaxel, 6 cycles)
Late stage, inoperable	Consider neoadjuvant chemotherapy (NACT) ^[9] → 3 cycles carboplatin/paclitaxel → interval debulking surgery (IDS) → 3 further cycles chemotherapy
Borderline ovarian tumours	Surgery alone (cystectomy or staging surgery depending on age/fertility wish). Generally do NOT need chemotherapy
Germ cell tumours	Surgery (fertility-sparing unilateral salpingo-oophorectomy if stage IA) + adjuvant chemotherapy (BEP: bleomycin, etoposide, cisplatin). Highly chemo-sensitive, excellent prognosis

4. Non-Surgical / Adjunctive Management Options

Therapy	Indication	Mechanism
Analgesia (NSAIDs, paracetamol)	Symptomatic relief in functional cysts, mild cyst-related pain	Pain from capsular stretch or peritoneal irritation; NSAIDs also reduce prostaglandin-mediated inflammation
Combined oral contraceptive (COC) pills	Prevention of new functional cysts (NOT treatment of existing ones)	Suppress HPO axis → no follicle recruitment → no follicular/corpus luteal cysts form
Progestogens (e.g. dienogest, medroxyprogesterone)	Endometrioma — symptom control, post-operative recurrence prevention	Oppose oestrogen's proliferative effect on ectopic endometrial tissue → decidualisation and atrophy
GnRH agonists (e.g. leuprolide)	Endometrioma — shrinkage before surgery, recurrence prevention	Downregulate GnRH receptors → medical menopause → oestrogen deprivation → endometrial tissue atrophies. Max 6 months due to bone loss risk
GnRH antagonists (e.g. elagolix)	Endometrioma — newer option	Direct GnRH receptor blockade, dose-dependent suppression without initial flare
Antibiotics	Tubo-ovarian abscess	Treat the infection; broad-spectrum coverage (e.g. IV ceftriaxone + metronidazole + doxycycline)

Procedure	Indication	Mechanism
Uterine fibroid embolisation (UAE) ^[16]	Uterine fibroids (NOT ovarian cysts — but mentioned here for completeness as the technique is relevant to pelvic mass management)	Embolic agents used to block specific blood vessels ^[16] — particulate embolisation of uterine arteries → ischaemic necrosis of fibroid
USS-guided drainage	Very selected cases: high surgical risk patients with clearly simple, symptomatic cysts	Aspiration of cyst fluid under USS guidance. Generally NOT recommended for ovarian cysts due to high recurrence rate (~50%) and inability to obtain tissue for histology
HIFU (High-Intensity Focused Ultrasound) ^[9]^[16]	Indication-specific selection criteria ^[9]. Primarily used for uterine fibroids. Emerging evidence for some benign ovarian conditions but NOT standard of care for ovarian cysts	Non-incisional, transcutaneous technique. Uses acoustic lens to concentrate multiple intersecting US beams at the lesion → thermal coagulative necrosis + acoustic cavitation ^[16]

HIFU and Ovarian Cysts

HIFU has indication-specific selection criteria ^[9] and is primarily validated for uterine fibroids. Its role in ovarian cyst management remains limited and experimental. For exams, know it exists but do NOT list it as a standard treatment for ovarian cysts.

Operation	What It Involves	When to Choose
Ovarian cystectomy	Remove cyst, preserve normal ovarian tissue	Young women, benign-appearing cyst, fertility desired
Unilateral salpingo-oophorectomy (USO)	Remove one ovary + tube	Cyst has destroyed ovary; germ cell tumour stage IA in young woman (fertility-sparing)
Bilateral salpingo-oophorectomy (BSO)	Remove both ovaries + tubes	Postmenopausal women ^[1]; or when contralateral ovary also abnormal
Total abdominal hysterectomy + BSO (TAH + BSO)	Remove uterus + cervix + both ovaries + tubes	Postmenopausal with suspected malignancy ^[1]; also concurrent uterine pathology
Full staging laparotomy	TAH + BSO + omentectomy + pelvic/para-aortic LN sampling + peritoneal biopsies + peritoneal washings ± appendicectomy	Confirmed or strongly suspected ovarian malignancy, by a trained gynaecological oncologist ^[1]

Laparoscopy vs Laparotomy:

Feature	Laparoscopy	Laparotomy
Preferred when	Likely benign, cyst < 10 cm, no adhesions	Suspected malignancy, very large cyst, dense adhesions
Advantages	Less pain, shorter recovery, smaller scars, less adhesion formation	Better visualisation and access, intact specimen (no spillage risk)
Risks	Cyst rupture/spillage during extraction (use endobag), port-site metastasis (rare, in malignancy)	Longer recovery, more pain, larger scar, more adhesions
Conversion	Always consent for conversion to laparotomy	N/A

Intraoperative Spillage — Why It Matters

If an ovarian cyst that turns out to be malignant is ruptured intraoperatively, it upstages the disease from FIGO stage IA to stage IC1 (surgical spill) or IC2 (capsule ruptured before surgery). This worsens prognosis and may mandate adjuvant chemotherapy that otherwise would not have been needed. This is why:

Suspected malignant cysts should be removed via laparotomy (intact specimen)
Use an endobag if removing any cyst laparoscopically (catches spillage)
Send peritoneal washings for cytology at the start of surgery

Scenario	Follow-Up Protocol
Functional cyst managed conservatively	Repeat USS in 6–12 weeks. If resolved → discharge. If persistent → operate
Postmenopausal simple cyst managed conservatively	Repeat CA125, TVS + TAS ^[1] at 4–6 monthly intervals for at least 1 year. Discharge if stable/resolving
Post-cystectomy for benign disease	Clinical review at 6 weeks post-op. Annual USS for 1–2 years to check for recurrence (especially endometriomas — ~30% recurrence rate)
Post-surgery for borderline tumour	Long-term USS surveillance (5–10 years) — late recurrence is possible
Post-surgery for ovarian cancer	CA125 monitoring + clinical review every 3 months for 2 years, then 6-monthly. CT if CA125 rises or symptoms recur

7. Special Situations

Functional cysts (especially corpus luteal cysts) are common in the first trimester and usually resolve by 14–16 weeks as the placenta takes over progesterone production.
Surgery in pregnancy is generally avoided in the first trimester (risk of miscarriage) unless emergency (torsion, rupture). Best timing if surgery needed: second trimester (14–20 weeks) — organogenesis complete, uterus not yet too large for laparoscopy.
Corpus luteal cyst removal before 12 weeks can precipitate miscarriage (removes progesterone source) — supplemental progesterone must be given if surgery is unavoidable.

Most are functional or germ cell tumours.
Fertility preservation is paramount — always attempt cystectomy rather than oophorectomy.
Check AFP, β-hCG, LDH to exclude malignant germ cell tumours (treatable with chemotherapy, excellent prognosis even if malignant).

High Yield Summary

Management depends on age, symptom, condition, and wish of the patient ^[1].
Emergency management: Torsion → emergency laparoscopic detorsion (attempt ovarian salvage). Ruptured cyst with haemodynamic instability → laparoscopy/laparotomy for haemostasis.
Premenopausal: Asymptomatic → observe with repeat USS in 3–6 months. Symptomatic → remove. Persistent → cystectomy vs salpingo-oophorectomy (laparoscopy vs laparotomy). Suspected cancer → refer oncology ^[1].
COC pills do NOT treat existing functional cysts — they prevent new ones by suppressing ovulation.
Postmenopausal: Calculate RMI I. RMI < 200 with ALL 5 low-risk features (asymptomatic, simple, < 5 cm, unilocular, unilateral) → conservative with serial CA125 + USS. Any non-simple feature → BSO. RMI ≥ 200 → CT + gynaecological oncology MDT → laparotomy (full staging if high suspicion; pelvic clearance if low suspicion) ^[1].
Ovarian cancer: If operable → operate first (time-sensitive, therapeutic and diagnostic). If inoperable → neoadjuvant chemotherapy ^[9].
Surgical principle: Cystectomy for young women wanting fertility (benign-appearing); BSO/TAH+BSO for postmenopausal; full staging laparotomy for confirmed/suspected malignancy by a trained gynaecological oncologist ^[1].
Avoid intraoperative spillage — upstages malignancy from IA to IC1. Use endobag during laparoscopy.
Full staging includes: TAH + BSO + omentectomy + peritoneal cytology (minimum for low-suspicion); add lymph node sampling + peritoneal biopsies for high-suspicion ^[1].

Active Recall - Management of Ovarian Cyst

References

^[1] Lecture slides: GC 118. Pelvic mass ovarian cancer and cysts; uterine fibroid; pelvic imaging.pdf (p66, p68, p71) ^[9] Lecture slides: Block C - Pelvic mass_ ovarian cancer and cysts; uterine fibroid; pelvic imaging.pdf (p18, p53, p55, p56, p57) ^[16] Senior notes: Ryan Ho Diagnostic Radiology.pdf (p85, p89 — uterine fibroid embolisation, HIFU)

Complications of Ovarian Cyst

Most ovarian cysts — particularly functional ones — are asymptomatic and self-resolving. However, complications are the reason ovarian cysts become clinically urgent. Understanding them is essential because they transform a benign, watchful-waiting condition into a surgical emergency.

Ovarian cyst acute complications have 3 classical forms, all presenting with abdominal pain → torsion, haemorrhage, rupture ^[9]. To these, we add infection and malignant transformation as additional complications ^[9]^[17].

2. Acute Complications

2.1 Torsion

"Torsion" — from Latin torsio = twisting. The ovarian pedicle (containing the ovarian artery, vein, and lymphatics in the infundibulopelvic ligament and the utero-ovarian ligament) twists on its axis, compromising blood flow.

The sequence is predictable from first principles:

Venous and lymphatic obstruction occurs first (thin-walled veins compress before thick-walled arteries) → venous congestion → ovarian oedema
Continued swelling increases intra-ovarian pressure → arterial compromise → ischaemia
Prolonged ischaemia → haemorrhagic infarction → necrosis → peritonitis

This is the same pathophysiology as testicular torsion — veins are compressed first because they have lower intraluminal pressure and thinner walls than arteries.

Risk Factor	Mechanism
Dermoid cyst (mature teratoma)	Most common ovarian tumour to torse ^[3]^[17] — heavy (contains fat, bone, teeth), pendulous, mobile on a long pedicle. Dermoid cyst → usually mobile ^[9] → keeps rolling due to sediment ^[17]
Cyst size 5–10 cm	Large enough to create torque, but not so large that it becomes fixed by adhesions to surrounding structures
Ovarian hyperstimulation (OHSS)	Massively enlarged, heavy ovaries after IVF/gonadotropin therapy
Pregnancy (1st trimester)	Corpus luteum of pregnancy enlarges the ovary; growing uterus shifts the ovary superiorly
Long ovarian pedicle	Greater range of motion → easier to twist
Previous torsion	Stretched ligaments → recurrence risk
Vigorous physical activity	Sudden changes in body position → initiates the twisting

Feature	Pathophysiological Basis
Sudden severe unilateral lower abdominal pain during agitating movement (e.g. exercise) ^[14]	Acute torsion of pedicle → sudden venous congestion and capsular stretching
Colicky / intermittent pain	Recurrent torsion/detorsion ^[3] — the ovary twists, partially untwists, then twists again
Nausea and vomiting	Vagal response to torsion of visceral peritoneum and stretching of the ovarian pedicle → vagal afferents stimulate the vomiting centre
Adnexal tenderness, ± lower abdominal tenderness and guarding ^[14]	Peritoneal irritation from congested, swollen ovary
Absent/reduced Doppler flow on USS	Twisted pedicle → arterial occlusion → no flow. "Whirlpool sign" = twisted vascular pedicle visualised on Doppler
Enlarged, oedematous ovary on USS	Venous/lymphatic congestion → interstitial oedema
Low-grade fever	Tissue ischaemia → inflammatory mediator release

Emergency laparoscopy → detorsion (untwist the pedicle)
Assess ovarian viability after detorsion — even if dusky/black, the ovary often recovers (do NOT reflexively remove it)
Cystectomy if the causative cyst is identifiable and the ovary is viable (prevents recurrence)
Salpingo-oophorectomy only if clearly gangrenous/necrotic with no recovery after detorsion

Exam Case: 24/F, Intermittent LLQ Pain, Tooth-shaped Radiodensity on AXR

This is a classic case from the radiology notes ^[3]: 24/F, previously well, intermittent LLQ pain, LLQ tenderness, no rebound. AXR shows tooth-shaped radiodensity in LLQ. Impression: ovarian teratoma with recurrent torsion/detorsion ^[3]. The intermittent nature of the pain is the clue — the ovary twists (pain), then partially untwists (relief), then twists again (pain recurs). The teeth on AXR confirm a dermoid.

2.2 Haemorrhage

Haemorrhage into an ovarian cyst occurs when blood vessels in the cyst wall rupture. This is particularly common in:

Corpus luteal cysts — the corpus luteum is inherently vascular (it develops a rich blood supply from theca interna vessels to support progesterone production). When these vessels rupture, blood fills the cyst cavity → haemorrhagic corpus luteal cyst
Endometriomas — cyclical menstrual bleeding into the cyst cavity (the fundamental pathology of "chocolate cysts")
Malignant cysts — neovascular tumour vessels are fragile and bleed easily

The haemorrhage may remain contained within the cyst (intracystic haemorrhage → painful but stable) or rupture through the cyst wall → haemoperitoneum.

Feature	Basis
Sudden unilateral pelvic pain	Rapid distension of cyst capsule by blood
Pain worse than torsion initially, then stabilises	Acute capsular stretch; blood clots and tamponades
USS: internal echoes within cyst, reticular "cobweb" pattern (fibrin strands)	Fresh blood → echogenic; organising clot → reticular pattern
USS: free fluid in pouch of Douglas (if ruptured)	Blood tracking from ruptured cyst into dependent pelvic recess
Falling haemoglobin, tachycardia, hypotension (if significant)	Blood loss → hypovolaemia

Haemodynamically stable + small haemoperitoneum: Conservative (analgesia, monitoring, serial Hb, bed rest)
Haemodynamically unstable or large haemoperitoneum: Emergency laparoscopy/laparotomy → haemostasis (cautery, suturing of bleeding point, cystectomy, or oophorectomy if bleeding uncontrollable) ^[6]

2.3 Rupture

Cyst rupture occurs when the cyst wall gives way — either spontaneously (thin-walled functional cyst) or due to trauma (including intercourse, vigorous exercise, or bimanual examination). The consequences depend on what spills into the peritoneal cavity:

Cyst Type	Content Spilled	Peritoneal Response
Follicular cyst	Clear serous follicular fluid	Mild chemical peritonitis, self-limiting. Mid-cycle lower abdominal/pelvic pain due to rupture of follicular cyst and bleeding → irritates peritoneum ^[18] (this is "Mittelschmerz")
Corpus luteal cyst	Blood	Haemoperitoneum ^[6] — can be life-threatening if vessel continues to bleed actively
Dermoid cyst (teratoma)	Sebaceous material, hair, fat	Sebaceous material brings more irritation to peritoneum than serous or mucinous fluid ^[18] → severe chemical peritonitis, granulomatous reaction, dense adhesion formation
Mucinous cystadenoma	Mucin	Pseudomyxoma peritonei — mucinous ascites with peritoneal implants ("jelly belly"). Progressive, debilitating, requires cytoreductive surgery + HIPEC
Malignant cyst	Malignant cells	Peritoneal carcinomatosis — upstages from FIGO IA to IC2 (capsule rupture before surgery) or IC1 (intraoperative spill)
Endometrioma	Old blood (chocolate fluid)	Intense peritoneal inflammation, adhesion formation

Feature	Basis
Sudden onset severe abdominal pain ^[1]	Peritoneal irritation by cyst contents
Peritoneal signs: guarding, rebound tenderness, rigidity	Chemical peritonitis from irritant cyst contents
Shoulder tip pain	Diaphragmatic irritation by free fluid (referred pain via phrenic nerve C3–C5) — especially with haemoperitoneum
Signs of hypovolaemic shock ^[14]	If ruptured corpus luteal cyst with active bleeding → haemoperitoneum
USS: collapsed cyst wall, free fluid	Cyst has decompressed; fluid/blood in pelvis

Mild, self-limited rupture (follicular): Analgesia, observation
Significant haemoperitoneum (corpus luteal): Resuscitation → emergency surgery → haemostasis ^[6]
Dermoid rupture: Urgent surgical washout + adhesiolysis (to minimise chemical peritonitis and adhesion formation)
Mucinous rupture with pseudomyxoma peritonei: Specialist referral → cytoreductive surgery + hyperthermic intraperitoneal chemotherapy (HIPEC)

Ruptured Ovarian Cyst as Cause of Haemoperitoneum

Pelvic organ rupture (e.g. ruptured ovarian cyst, ruptured ectopic pregnancy) is a recognised cause of haemoperitoneum ^[6]. In the acute abdomen differential, always consider these alongside abdominal trauma, ruptured AAA, and ruptured HCC.

2.4 Infection

Primary infection of an ovarian cyst is uncommon but can occur via:
- Ascending infection from the lower genital tract (PID pathogens — Neisseria gonorrhoeae, Chlamydia trachomatis, polymicrobial anaerobes)
- Haematogenous spread (rare)
- Secondary infection of a ruptured or haemorrhagic cyst
An infected ovarian cyst may progress to a tubo-ovarian abscess (TOA) when the inflammatory process involves the adjacent fallopian tube

Feature	Basis
Fever, rigors	Systemic inflammatory response to infection
Unilateral or bilateral pelvic pain	Infection → inflammation → capsular and peritoneal irritation
Purulent vaginal discharge	Ascending genital tract infection
Cervical motion tenderness (chandelier sign) ^[14]	Movement of the cervix tugs on the inflamed adnexal structures → exquisite pain
Elevated WCC, CRP	Acute phase inflammatory response
USS: complex cyst with thick walls, debris, loculations	Pus and inflammatory debris within the cyst

IV antibiotics (broad-spectrum: cephalosporin + metronidazole + doxycycline)
Drainage if abscess does not respond to antibiotics within 48–72 hours (percutaneous USS-guided or surgical)
Laparoscopy/laparotomy if ruptured TOA → peritonitis → surgical emergency

3. Chronic / Subacute Complications

Not all ovarian cysts carry equal malignant risk. The key associations are:

Cyst Type	Risk of Malignant Transformation	Malignancy Type
Functional cysts	Essentially zero	N/A
Mature teratoma (dermoid)	~1–2% (almost exclusively in postmenopausal women)	Squamous cell carcinoma (arising from ectodermal component)
Serous cystadenoma	Can progress to borderline and then serous cystadenocarcinoma	Serous carcinoma (most common ovarian malignancy)
Mucinous cystadenoma	Lower than serous; benign → borderline → malignant spectrum	Mucinous carcinoma
Endometrioma	~1% (especially large, longstanding endometriomas)	Clear cell carcinoma or endometrioid carcinoma

The concept of a benign → borderline → malignant spectrum is well established for epithelial ovarian tumours. However, the latest understanding is that many high-grade serous carcinomas actually arise de novo from the fimbrial end of the fallopian tube (serous tubal intraepithelial carcinoma, STIC) rather than from pre-existing ovarian cysts. This is why prophylactic bilateral salpingectomy (removing the tubes) is now increasingly offered at the time of hysterectomy for benign indications — it removes the precursor lesion.

Large ovarian cysts (especially mucinous cystadenomas, which can grow to enormous sizes) cause symptoms through mechanical compression of adjacent pelvic structures:

Structure Compressed	Clinical Effect
Bladder	Urinary frequency, urgency, incomplete voiding
Rectum / sigmoid colon	Constipation, tenesmus
Pelvic veins (iliac veins)	Leg oedema, varicose veins, DVT risk. Ovarian cysts as extramural cause of venous obstruction ^[4]
Ureters	Hydronephrosis, renal impairment (rare, usually with very large or fixed/malignant masses)
Pelvic nerves (lumbosacral plexus)	Lower back pain, sciatica
Diaphragm (if very large or ascites)	Dyspnoea, Meigs syndrome (fibroma + ascites + right pleural effusion)
Lymphatics	Lower limb swelling — due to lymphatic invasion/impedance of lymphatic return ^[9] (more characteristic of malignancy)

These arise from functional cysts or hormonally-active neoplasms:

Hormone	Source	Complication
Excess oestrogen	Follicular cyst, granulosa cell tumour, thecoma	Menstrual irregularity, menorrhagia, endometrial hyperplasia → risk of endometrial cancer. Drop in secretion of ovarian hormone results in endometrial sloughing ^[18] (when oestrogen support from the cyst suddenly drops, withdrawal bleeding occurs)
Excess progesterone	Corpus luteal cyst	Amenorrhoea (mimics pregnancy — progesterone maintains endometrium), delayed menses
Excess androgens	Sertoli-Leydig cell tumour	Virilisation (hirsutism, deepening voice, clitoromegaly, male-pattern baldness)
Excess thyroid hormone	Struma ovarii (teratoma with thyroid tissue)	Hyperthyroidism (tachycardia, weight loss, tremor)
Excess hCG response	Theca lutein cysts	Associated with gestational trophoblastic disease — the primary pathology, not the cyst itself

Ovarian cysts can impair fertility through multiple mechanisms:

Mechanism	Examples
Anovulation	Large follicular cyst suppresses FSH → no new follicle recruitment; PCOS (multiple small antral follicles, anovulation)
Destruction of ovarian tissue	Large endometrioma replaces normal ovarian cortex → reduced ovarian reserve; repeated surgery on ovaries damages follicles
Tubal distortion	Large cysts or adhesions from endometriosis/PID distort tubo-ovarian anatomy → impair oocyte pick-up
Hostile peritoneal environment	Endometriosis → inflammatory peritoneal fluid with elevated cytokines, macrophages → impairs sperm function and embryo implantation

Cyst Type	Most Important Complications
Follicular cyst	Rupture (Mittelschmerz), rarely haemorrhage. Self-resolves
Corpus luteal cyst	Haemorrhage (most common cyst to bleed significantly), rupture → haemoperitoneum ^[6]
Dermoid cyst	Torsion (most common tumour to torse) ^[3]^[17], rupture → chemical peritonitis, malignant transformation (~1–2%)
Endometrioma	Chronic pain, infertility, adhesion formation, malignant transformation (clear cell / endometrioid carcinoma ~1%)
Mucinous cystadenoma	Rupture → pseudomyxoma peritonei
Serous cystadenoma	Malignant transformation (benign → borderline → carcinoma)
Fibroma	Meigs syndrome (ascites + right pleural effusion) — resolves after tumour removal
Theca lutein cyst	Massive enlargement, torsion, rupture. Resolves once hCG stimulus removed

Complication	Context	Mechanism
Reduced ovarian reserve	Repeated cystectomy (especially for endometriomas)	Surgical excision removes normal ovarian cortex along with the cyst capsule → loss of primordial follicles
Intraoperative spillage	Laparoscopic cystectomy of malignant cyst	Rupture during extraction → peritoneal contamination → upstaging (IA → IC1)
Adhesion formation	Any pelvic surgery	Surgical trauma + inflammation → fibrinous adhesions → bands. Can cause bowel obstruction, chronic pain, infertility
Surgical menopause	Bilateral oophorectomy in premenopausal woman	Loss of ovarian oestrogen → acute menopausal symptoms (hot flushes, vaginal dryness, osteoporosis, cardiovascular risk). Requires HRT consideration
Injury to adjacent structures	Any pelvic surgery	Ureter (runs under the uterine artery — "water under the bridge"), bladder, bowel, major vessels

Surgical Menopause After Bilateral Oophorectomy

Bilateral oophorectomy in a premenopausal woman causes immediate surgical menopause — unlike natural menopause, there is no gradual transition. The sudden loss of oestrogen causes more severe vasomotor symptoms and accelerated bone loss. HRT should be offered to these women (at least until the natural age of menopause, ~50 years) unless contraindicated (e.g., oestrogen-receptor-positive breast cancer).

High Yield Summary

Three classical acute complications of ovarian cysts: torsion, haemorrhage, rupture ^[9]^[1]. All present with acute pelvic pain. Infection is a fourth acute complication ^[9]^[17].
Torsion: Most common with dermoid cysts ^[3]^[17] — heavy, mobile, pendulous. Venous obstruction occurs before arterial. Emergency laparoscopic detorsion — always attempt ovarian salvage.
Haemorrhage: Most common with corpus luteal cysts (highly vascular wall). Can cause haemoperitoneum ^[6]. Conservative if stable; surgical if unstable.
Rupture: Consequences depend on contents spilled. Follicular fluid → mild irritation (Mittelschmerz). Sebaceous material (dermoid) → severe chemical peritonitis ^[18]. Blood (corpus luteal) → haemoperitoneum. Mucin → pseudomyxoma peritonei. Malignant cells → peritoneal carcinomatosis and upstaging.
Malignant transformation: Endometrioma → clear cell / endometrioid carcinoma (~1%). Dermoid → SCC (~1–2%). Serous cystadenoma → borderline → serous carcinoma.
Meigs syndrome: Fibroma + ascites + right pleural effusion. Resolves completely with fibroma removal.
Hormonal complications: Oestrogen excess → endometrial hyperplasia/cancer. Progesterone excess → amenorrhoea. Androgen excess → virilisation.
Iatrogenic complications: Reduced ovarian reserve (repeated cystectomy), intraoperative spillage (upstaging malignancy), adhesion formation, surgical menopause (bilateral oophorectomy in premenopausal woman).

Active Recall - Complications of Ovarian Cyst

References

^[1] Lecture slides: GC 118. Pelvic mass ovarian cancer and cysts; uterine fibroid; pelvic imaging.pdf (p12, p20, p24) ^[3] Senior notes: Ryan Ho Radiology.pdf (p33 — ovarian teratoma with recurrent torsion/detorsion) ^[4] Senior notes: Maksim Surgery Notes.pdf (p172 — ovarian cysts as extramural cause of venous obstruction) ^[6] Senior notes: Maksim Surgery Notes.pdf (p177 — ruptured ovarian cyst as cause of haemoperitoneum) ^[9] Lecture slides: Block C - Pelvic mass_ ovarian cancer and cysts; uterine fibroid; pelvic imaging.pdf (p8, p9, p10, p15) ^[14] Senior notes: Ryan Ho Fundamentals.pdf (p273 — torsion/ruptured ovarian cyst clinical features) ^[17] Lecture slides: Block C - O&G Theme Case 3.pdf (p4 — ovarian cyst complications: torsion, rupture, haemorrhage, infection; dermoid keeps rolling due to sediment) ^[18] Senior notes: Ryan Ho GI.pdf (p151 — Mittelschmerz, sebaceous material more irritating than serous/mucinous fluid, endometrial sloughing)

High Yield Summary

Definition: Fluid-filled sac on or within the ovary (≥ 1 cm). Spectrum from physiological functional cysts to neoplastic cysts.

Classification (lecture framework — must know):

Functional: follicular cyst, corpus luteal cyst, theca lutein cyst
Inflammatory: endometriotic cyst, tubo-ovarian abscess
Germ cell: mature teratoma (dermoid)
Epithelial: serous/mucinous/clear cell cystadenoma
Sex cord-stromal: fibroma, thecoma

Epidemiology: Very common; functional cysts in virtually all ovulating women; dermoid = most common benign ovarian neoplasm (20–40y); epithelial tumours peak 40s–60s.

Functional cyst pathophysiology:

Follicular: failed ovulation/atresia → unilocular thin-walled anechoic cyst; oestrogen → menstrual irregularity; resolves in 4–8 weeks.
Corpus luteal: excessive bleeding into corpus luteum → delayed period (progesterone); more haemorrhagic/rupture-prone.
Theca lutein: high β-hCG (pregnancy, molar, OHSS) → bilateral multiple large cysts.

Exam: Mass separate from uterus; dermoid usually mobile; endometrioma not mobile (adhesions). Ascites → think neoplasm, not simple cyst.

High Yield Summary — Differential Diagnosis

Golden rule: Shock/severe pain/peritoneal signs → urgent surgery. Always β-hCG first in reproductive-age women.

Pelvic mass DDx by origin:

Uterine: fibroid (moves with cervix, firm, vascular), adenomyosis (boggy uterus), pregnancy
Ovarian/adnexal: functional cyst, endometrioma, dermoid, cystadenoma, ovarian cancer
Other gynae: paraovarian cyst, hydrosalpinx (cogwheel sign)
Non-gynae: distended bladder, mesenteric cyst, GI tumour, pelvic kidney

Acute pelvic pain emergencies:

Ruptured/haemorrhagic cyst, ovarian torsion, ectopic pregnancy (#1 rule-out), PID/TOA, appendicitis, mittelschmerz

Don't miss: full bladder misdiagnosed as mass; Krukenberg tumour if bilateral suspicious mass + ascites.

High Yield Summary — Diagnosis

No formal diagnostic criteria — diagnosis = clinical + USS characterisation + risk stratification.

First steps: vital signs → β-hCG → bimanual exam → TVS ± TAS.

USS reporting essentials: side, size, morphology (cystic/solid/mixed), wall, septae, internal echoes, papillary projections, Doppler, free fluid.

Simple cyst (premenopausal): unilocular, thin wall, anechoic, no solid component → likely functional.

Suspicious features: solid components, papillary projections, thick septae (> 3 mm), central vascularity, large ascites, bilateral complex masses.

Tumour markers (risk stratify, not diagnose alone):

CA125: poor specificity in premenopausal (endometriosis, PID, menstruation); more useful postmenopausally + RMI
AFP, β-hCG, LDH: germ cell tumours
Inhibin: granulosa cell tumour

Postmenopausal: any adnexal mass = malignancy until proven otherwise → CA125 + RMI → MDT if high risk.

High Yield Summary — Management

Four drivers: age/menopausal status, symptoms, USS morphology, patient wish.

Premenopausal asymptomatic simple cyst < 5 cm: observe → repeat USS in 6–12 weeks; if resolved = functional; if persistent → surgery.

Symptomatic or complicated: surgical removal (laparoscopic cystectomy preferred for fertility preservation).

Postmenopausal low RMI (< 200) + simple < 5 cm: conservative serial USS/CA125; if any concerning feature → MDT + lap BSO.

Postmenopausal RMI ≥ 200: CT → gynaecological oncology MDT → staging surgery.

Emergency:

Torsion → lap detorsion ± cystectomy (detorse even if dusky)
Rupture with instability → resuscitate + surgery
Ruptured ectopic → salpingectomy

High Yield Summary — Complications

Three classical acute complications (all → abdominal pain):

Torsion — dermoid most common tumour to torse (sediment → rolling); 5–10 cm highest risk; sudden pain ± N/V; absent Doppler flow; emergency detorsion
Haemorrhage — corpus luteal cyst most common; lace-like echoes on USS; haemoperitoneum if rupture
Rupture — sudden pain + free fluid; stable small leak may be conservative

Also: infection (TOA), malignant transformation (rare in benign cysts; suspect if postmenopausal/new solid components).

Chronic: pressure symptoms, hormonal effects (oestrogen-secreting tumours → endometrial hyperplasia), infertility (endometrioma, PCOS context).

Exam case: 24/F intermittent LLQ pain + tooth on AXR = dermoid with intermittent torsion/detorsion.

Ovarian Cyst

1. Definition

2. Epidemiology

3. Risk Factors

4. Anatomy and Functional Review

4.1 Ovarian Anatomy

4.2 Ovarian Histology (Three Layers)

4.3 Normal Ovarian Physiology (The Follicular Cycle)

5. Aetiology and Classification

5.1 Types of Benign Ovarian Masses [1]

5.2 Detailed Aetiology and Pathophysiology

5.2.1 Functional Cysts

a) Follicular Cyst

b) Corpus Luteal Cyst

c) Theca Lutein Cyst

5.2.2 Inflammatory Cysts

a) Endometriotic Cyst (Endometrioma / "Chocolate Cyst")

b) Tubo-ovarian Abscess (TOA)

5.2.3 Benign Neoplastic Cysts

a) Mature Cystic Teratoma (Dermoid Cyst) — Germ Cell Origin

b) Epithelial Cystadenomas — Surface Epithelial Origin

c) Sex Cord-Stromal Tumours

5.2.4 Other

6. Relevant Classification Systems

6.1 Classification by Functionality

6.2 Simple vs Complex Cysts (Ultrasound-Based)

6.3 Risk of Malignancy Index (RMI) [1]

7. Clinical Features

7.1 Symptoms

7.2 Signs

7.3 Clinical Approach to Examining an Ovarian Cyst

8. Special Considerations for Hong Kong

9. Key Pathophysiology Summary Diagram

Active Recall - Ovarian Cyst: Definition, Epidemiology, Aetiology, Classification, Clinical Features

References

1. Approach to the Differential Diagnosis

2. DDx of a Pelvic Mass (The Overarching Framework)

2.1 Gynaecological Causes [1]

2.2 Non-Gynaecological Causes [1]

3. DDx of Acute Pelvic Pain (The Emergency Scenario)

4. DDx Within Ovarian Cysts — Differentiating by Type

5. DDx by Clinical Presentation — Special Scenarios

5.1 The Adolescent / Teenage Girl with Pelvic Mass

5.2 The Premenopausal Woman (Adnexal Mass)

5.3 The Postmenopausal Woman (Adnexal Mass)

5.4 Acute Abdomen — Surgical DDx Overlap

6. How to Differentiate — Practical Clinical and Investigation Approach

7. Summary DDx Table — Putting It All Together

Active Recall - Differential Diagnosis of Ovarian Cyst

1. Diagnostic Principles — Thinking from First Principles

2. Initial Evaluation — Bedside and History

3. Investigation Modalities

3.1 Blood Investigations

3.2 Imaging Investigations

a) Pelvic Ultrasound (TVS + TAS) — First-Line Investigation [1]

USS Appearances by Cyst Type

b) Plain Radiograph (AXR)

c) CT Scan (Abdomen and Pelvis)

d) MRI Pelvis

e) O-RADS (Ovarian-Adnexal Reporting and Data System) [9]

4. Diagnostic Algorithm

4.1 Premenopausal Adnexal Mass Algorithm [1]

4.2 Postmenopausal Ovarian Cyst Algorithm [1]

5. When to Use Specific Investigations — Quick Reference

6. Histological Diagnosis — When and How

7. Summary — The Diagnostic Pathway at a Glance

Active Recall - Diagnosis of Ovarian Cyst

1. Management Principles — Thinking from First Principles

2. Master Management Algorithm

3. Management by Clinical Scenario

3.1 Emergency Management

3.2 Premenopausal Adnexal Mass / Cyst [1]

a) Asymptomatic Cyst — Observation [1]

b) Symptomatic Cyst — Surgical Removal [1]

c) Persistent Cyst — Surgical Removal [1]

d) Suspected Malignancy [1]

3.3 Specific Management by Cyst Type (Premenopausal)

3.4 Postmenopausal Ovarian Cyst [1]

Step 3A: RMI I < 200 (Low Risk of Malignancy) [1]

Step 3B: RMI I ≥ 200 (Increased Risk of Malignancy) [1]