Rlq Pain

Right lower quadrant pain is discomfort localized to the lower right abdomen, most commonly associated with appendicitis but also arising from gynecological, urological, or gastrointestinal conditions.

Epidemiology

Condition	Key Demographics
Ectopic pregnancy	Reproductive-age females, peak 25–34 years
Testicular torsion	Two peaks: neonatal and pubertal (65% between 12–18 years) ^[1]
Ureteric colic	Male predominance (M:F = 3:1), peak 40–60s ^[1]
Mesenteric adenitis	Children and young adults (often post-viral)
Ovarian torsion	Reproductive-age females, especially with ovarian cysts
Ischaemic colitis	Elderly females (90% > 60 years) ^[3]

Risk Factors

Category	Risk Factor	Mechanism
Age	Young adults (20s–30s)	Peak lymphoid tissue activity → higher chance of lymphoid hyperplasia obstructing the lumen
Sex	Male gender	Higher lifetime risk; also an independent risk factor for perforation ^[1]
Diet	Low-fibre diet	Predisposes to faecolith formation
Faecolith	Present in ~30–40% of cases	Composed of inspissated faecal material + calcium phosphate + bacteria + epithelial debris; physically obstructs the lumen ^[1]
Extremes of age	Children < 5, elderly > 65	Delayed/atypical presentation → higher perforation rate
Diabetes mellitus	Immunosuppression	Impaired immune response → delayed containment → perforation ^[1]
Immunosuppression	Steroids, chemotherapy	Same mechanism as above
Previous abdominal surgery	Adhesions alter anatomy	May delay diagnosis
Pelvic appendix	Absence of rotation of appendix during childhood	Atypical location → atypical symptoms → delayed diagnosis → perforation ^[1]
Family history	Genetic predisposition	Unclear mechanism, possibly related to appendiceal anatomy

Anatomy and Function

Understanding RLQ pain requires you to know exactly what lives in this quadrant and how it is innervated. The pain you feel from any organ depends on which nerve fibres are stimulated — and this is the key to understanding why appendicitis pain migrates.

Structure	Key Anatomical Points
Appendix	True diverticulum of the caecum containing all layers of the bowel wall (mucosa → submucosa → muscularis → serosa). Base is at McBurney's point (1/3 distance from ASIS to umbilicus). The base is constant (at the confluence of three taeniae coli of the caecum), but the tip is variable. ^[1]^[3]
Caecum	First part of the large bowel, intraperitoneal; site of the ileocaecal valve
Terminal ileum	Last portion of the small bowel; Peyer's patches here are relevant to Crohn's disease and mesenteric adenitis
Right ureter	Runs retroperitoneally over the pelvic brim (crossing the bifurcation of the common iliac artery) — a site of ureteric stone impaction
Right ovary and fallopian tube (females)	Intraperitoneal pelvic structures; relevant to ectopic pregnancy, ovarian torsion, ovarian cyst rupture
Right spermatic cord (males)	Passes through the inguinal canal; relevant to inguinal hernia and testicular pathology
Psoas muscle	Retroperitoneal; a retrocaecal appendix can irritate it
Iliac vessels	Right common iliac artery and vein

This is critical for understanding clinical signs:

The appendix is a true diverticulum of the caecum — it contains all layers including mucosa, submucosa, longitudinal and circular muscularis, and serosa ^[1]^[3]
Position of the appendix tip: ^[1]^[3]

Position	Frequency
Retrocaecal (but intraperitoneal)	74%
Pelvic	21%
Paracaecal	2%
Subcaecal	1.5%
Preileal	1%
Postileal	0.5%

Why does position matter? Because the tip of the appendix determines which somatic structures it irritates when inflamed:
- Retrocaecal → may irritate the psoas muscle (positive psoas sign) and may not produce classic anterior abdominal tenderness → delayed diagnosis
- Pelvic → may irritate the bladder (dysuria, frequency) or rectum (diarrhoea, tenesmus) → mimics UTI or gastroenteritis → delayed diagnosis → higher perforation rate ^[1]
Blood supply: appendicular artery, a terminal branch of the ileocolic artery (from SMA) ^[1]^[3]
- This is an end-artery — if thrombosed (from inflammation/oedema compressing it), the entire appendix becomes ischaemic → gangrenous appendicitis ^[2]^[3]
Lymphoid tissue: the appendix contains prominent lymphoid tissue (compared to the rest of the caecum) ^[3]
- This lymphoid tissue is most active in childhood and adolescence → prone to lymphoid hyperplasia which can obstruct the lumen → this is why appendicitis peaks in the young
- Lymphoid tissue undergoes atrophy with age — which is why appendicitis is rare in the elderly ^[1]
Mesoappendix: contains the appendicular artery, 4–6 lymphatic channels (drain to ileocaecal lymph nodes), and fat (fat content increases in adults; in children the mesoappendix may be transparent) ^[3]

This is the foundation for understanding the classical migratory pain of appendicitis:

Type of Pain	Nerve Pathway	Character	Location
Visceral pain (early)	Afferent fibres travel with sympathetic nerves (lesser splanchnic nerve → T10–T11 dermatome) from the midgut	Poorly localised, dull, crampy, intermittent	Periumbilical (T10 dermatome — because the appendix is a midgut structure)
Somatic/parietal pain (late)	Parietal peritoneum is innervated by somatic nerves (corresponding to segmental dermatomes)	Well-localised, sharp, constant, worsened by movement/coughing	RLQ (specifically McBurney's point, because the inflamed appendix irritates the overlying parietal peritoneum)

Why does appendicitis pain migrate? Initially, distension and inflammation of the appendix stimulate visceral afferents (travelling with T10 sympathetics from the midgut) → periumbilical pain. Over 12–24 hours, transmural inflammation reaches the serosa and irritates the overlying parietal peritoneum → somatic nerve fibres localise the pain to the RLQ. This is the classic visceral-to-somatic pain migration of appendicitis.

Aetiology (Focus on Hong Kong)

The differential diagnosis of RLQ pain is broad and must be systematically considered by organ system. ^[4]

From the lecture slides, the following causes of RLQ pain are explicitly listed: ^[4]

System	Cause	Notes
GI — Appendix	Acute appendicitis	Most common surgical cause
GI — Caecum	Caecal diverticulitis	Particularly common in Hong Kong/Asia — right-sided diverticulosis is proportionally much higher than in Western populations ^[1]^[4]
GI — Caecum	Cancer of caecum	Insidious onset; may present with iron-deficiency anaemia, palpable mass, or obstruction ^[4]
GI — Ileum	Ileitis (Crohn's disease, infectious ileitis, TB ileitis)	Terminal ileum is the most common site for Crohn's disease; TB ileitis is important in Hong Kong ^[4]
GI — Meckel's	Meckel's diverticulitis	True diverticulum of the ileum (~2 feet from ileocaecal valve); contains ectopic gastric mucosa in ~50% → can ulcerate and present like appendicitis ^[4]
GI — Mesentery	Mesenteric adenitis	Inflamed mesenteric lymph nodes, often post-viral; common in children; mimics appendicitis ^[4]
GI — Vascular	Caecal ischaemia	Part of ischaemic colitis spectrum; watershed areas (Griffiths' point, Sudeck's point) ^[4]
Urological	Ureteric colic	Can cause pain at left and right side ^[4]
Gynaecological	Ruptured ectopic pregnancy	Can cause pain at left and right side; haemodynamic instability ^[4]
Gynaecological	Torsion of ovarian cyst	Can cause pain at left and right side ^[4]
Hernia	Inguinal/femoral hernia	Can cause pain at left and right side; incarceration → strangulation ^[4]
Scrotal	Testicular pathology (torsion, epididymitis)	Can cause pain at left and right side ^[4]
Upper GI referred	Perforated peptic ulcer	Duodenal contents track down the right paracolic gutter → RLQ pain and tenderness (the "drip-down" phenomenon) ^[4]
Hepatobiliary	Acute cholecystitis	Can present with RLQ pain if the gallbladder is low-lying or if there is referred pain ^[4]

Hong Kong-Specific Considerations

In Hong Kong, always consider:

Right-sided diverticulitis — far more common than in the West; often misdiagnosed as appendicitis
Intestinal tuberculosis — TB ileitis affecting the terminal ileum/ileocaecal region; Hong Kong has intermediate TB prevalence
Parasitic infections — amoebiasis (Entamoeba histolytica) can cause amoebic typhlitis/colitis in the right colon
Klebsiella liver abscess — common in Hong Kong; can present with RLQ pain if the abscess is low in the right lobe or if there is referred pain

Pathophysiology (By Major Aetiology)

This is the paradigmatic RLQ pathology. Understanding the pathophysiology from first principles:

Step-by-step: ^[1]^[2]^[3]

Luminal obstruction (present in ~2/3 of cases; 1/3 are non-occlusive) ^[2]
- Causes of obstruction:
  - Faecolith ("faeco" = faeces, "lith" = stone): a hard stony mass of faeces — the most common cause in adults ^[2]
  - Lymphoid hyperplasia (the usual cause in the young) — lymphoid tissue in the appendiceal wall swells in response to infections (gastroenteritis, URTI, measles) or inflammation (e.g., Crohn's disease) ^[3]
  - Rare: tumour (carcinoma of caecum), intestinal parasites, foreign bodies ^[2]
Mucosal secretion continues → fluid accumulates in the obstructed lumen → raised intraluminal pressure
Venous outflow obstruction → when intraluminal pressure exceeds venous pressure, venous congestion occurs → mucosal oedema and ischaemia
Bacterial invasion → the ischaemic mucosa loses its barrier function → enteric bacteria (E. coli, Pseudomonas aeruginosa, Peptostreptococcus, Bacteroides) ^[1] invade the wall → suppurative inflammation
Arterial compromise → the appendicular artery is an end-artery → inflammation and oedema compress it → gangrenous appendicitis ^[2]^[3]
Perforation → necrotic wall perforates → if the omentum and adjacent bowel loops wall it off → appendiceal abscess; if not → generalised peritonitis ^[2]

Disease Severity Grading: ^[1]

Grade	Description
Grade 1	Inflamed
Grade 2	Gangrenous
Grade 3	Perforated with localised free fluid
Grade 4	Perforated with regional abscess
Grade 5	Perforated with diffuse peritonitis

Classification

System	Conditions
Gastrointestinal	Acute appendicitis, caecal diverticulitis, Crohn's ileitis, TB ileitis, Meckel's diverticulitis, caecal carcinoma, caecal ischaemia, mesenteric adenitis, right-sided colitis (infectious, IBD)
Urological	Ureteric colic (right), right pyelonephritis, right renal abscess
Gynaecological	Ruptured ectopic pregnancy, ovarian torsion, ovarian cyst rupture, pelvic inflammatory disease (PID), endometriosis
Vascular	Mesenteric ischaemia (SMA occlusion), ruptured right iliac artery aneurysm
Hernias	Right inguinal hernia (direct/indirect), right femoral hernia — incarcerated/strangulated
Scrotal	Testicular torsion, epididymo-orchitis, torsion of appendix testis
Musculoskeletal / Abdominal wall	Rectus sheath haematoma, psoas abscess, abdominal wall hernia
Referred pain	Perforated duodenal ulcer (contents track down right paracolic gutter), acute cholecystitis, right basal pneumonia, right lower lobe PE

Urgency	Conditions
Requires emergency surgery	Perforated appendicitis with peritonitis, testicular torsion, ruptured ectopic pregnancy, strangulated hernia, intestinal perforation
May require urgent surgery	Uncomplicated appendicitis, ovarian torsion, appendiceal abscess (may be drained percutaneously first)
Usually managed conservatively	Mesenteric adenitis, uncomplicated diverticulitis, ureteric colic, PID, Crohn's flare

Character	Typical Cause	Mechanism
Colicky (waxing and waning)	Ureteric colic, intestinal obstruction, biliary colic	Peristalsis of smooth muscle against an obstruction
Constant, progressive	Appendicitis, diverticulitis	Progressive transmural inflammation
Sudden onset, severe	Ruptured ectopic, testicular torsion, perforated viscus	Acute vascular compromise or free peritoneal contamination
Migratory (periumbilical → RLQ)	Appendicitis	Visceral → somatic pain transition (see above)

Clinical Features

Symptoms

Signs

"You need to know these signs" — they are high-yield exam material ^[2]

Sign	How to Elicit	Pathophysiology
Pointing sign	Ask patient to point to maximum tenderness	Localised peritoneal irritation at McBurney's point (1/3 from ASIS to umbilicus) — the base of the appendix lies here ^[2]
Rovsing's sign	RLQ pain upon palpation (or rebound) of the LLQ	Palpating the LLQ pushes gas/fluid retrograde through the colon → distends the caecum → stretches the inflamed parietal peritoneum in the RLQ ^[2]
Psoas sign	Increased RLQ pain upon extending the hip against resistance (patient lies on left side, examiner extends the right hip)	A retrocaecal appendix lies anterior to the psoas muscle → passive extension stretches the psoas → moves the inflamed appendix → pain ^[2]
Obturator sign	Pain on passive internal rotation of the flexed right hip	A pelvic appendix lies near the obturator internus muscle → internal rotation stretches this muscle → irritates the inflamed appendix
Guarding	Involuntary rigidity of abdominal wall muscles on palpation	Somatic reflex arc: inflamed parietal peritoneum → afferent signal → spinal cord → efferent motor signal → rectus abdominis contraction (protective)
Rebound tenderness	Pain worse on release of pressure than on pressing	Sudden release causes the peritoneal surfaces to bounce back → movement of inflamed peritoneum → pain
Fever	Low-grade (37.5–38.5°C) initially; high-grade if perforated	Pyrogens (IL-1, TNF-α, PGE2) from the inflammatory response act on the hypothalamic thermoregulatory centre

Why is McBurney's Point Important?

McBurney's point marks the surface projection of the base of the appendix. The base is constant (at the confluence of three taeniae coli), but the tip is variable. This means that while the point of maximum tenderness is usually at McBurney's point, atypical appendix positions (pelvic, retrocaecal) may shift it.

Condition	Key Signs	Pathophysiological Basis
Caecal diverticulitis	RLQ tenderness, low-grade fever, palpable mass (if abscess)	Pericolic inflammation → localised peritonism; abscess → walled-off collection
Ureteric colic	Patient cannot lie still (writhes), renal angle tenderness	Visceral pain from ureteric peristalsis against obstruction → restlessness (no peritoneal irritation → no benefit from lying still)
Ruptured ectopic	Cervical motion tenderness ("chandelier sign"), adnexal tenderness, signs of shock	Blood in pelvis irritates the peritoneum; hypovolaemia from haemoperitoneum
Testicular torsion	High-riding, horizontal-lying testis; absent cremasteric reflex; swollen, tender testis	Torsion shortens the spermatic cord → testis rides high; bell-clapper deformity → horizontal lie; oedema abolishes the cremasteric reflex arc
Strangulated hernia	Tender, irreducible lump at inguinal region; overlying erythema	Incarcerated bowel loop → venous congestion → arterial compromise → ischaemia → inflammation
Peritonitis (any cause)	Board-like rigidity, absent bowel sounds, rebound tenderness, patient lies still	Generalised peritoneal inflammation → diffuse guarding; paralytic ileus → absent bowel sounds; any movement worsens pain
Mesenteric adenitis	Shifting tenderness (unlike appendicitis, where tenderness is fixed)	Inflamed lymph nodes are on the mesentery, which is mobile → tenderness shifts with position

Feature	Appendicitis	Caecal Diverticulitis	Ureteric Colic	Ectopic Pregnancy	Testicular Torsion	Mesenteric Adenitis
Age	10–30	> 50	40–60	Reproductive age	12–18	Children
Pain onset	Gradual, migratory	Gradual, non-migratory	Sudden, colicky	Sudden	Sudden	Gradual
Pain migration	Periumbilical → RLQ	No	No	No	Scrotal → abdominal	No
Fever	Low-grade	Yes	No (unless infected)	No (unless septic)	No initially	Higher than expected
Anorexia	Yes (early)	Variable	No	Variable	No	Variable
Urinary symptoms	If pelvic appendix	Rare	Yes	Rare	Rare	No
Vaginal bleeding	No	No	No	Yes (scant, dark)	No	No
Key sign	McBurney's tenderness	RLQ mass	Restlessness, loin tenderness	Cervical motion tenderness	High-riding testis	Shifting tenderness

High Yield Summary

Definition: RLQ pain = pain in the lower right abdomen; the most common surgical cause is acute appendicitis.

Epidemiology: Appendicitis peaks in the 2nd–3rd decades; M:F = 1.4:1. In Hong Kong/Asia, right-sided diverticulitis is proportionally much more common than in the West and is a key differential.

Anatomy: The appendix base is constant (McBurney's point, confluence of taeniae coli). The tip is variable (74% retrocaecal, 21% pelvic). Blood supply = appendicular artery (end-artery from ileocolic). Prominent lymphoid tissue in the young.

Pathophysiology of appendicitis: Luminal obstruction (faecolith, lymphoid hyperplasia) → raised intraluminal pressure → venous congestion → ischaemia → bacterial invasion → transmural inflammation → gangrenous appendicitis (end-artery thrombosis) → perforation → abscess or generalised peritonitis.

Visceral vs somatic pain: Midgut visceral afferents → T10 → periumbilical pain (early). Parietal peritoneum irritation → somatic localisation to RLQ (late 12–24h). This is why the pain migrates.

Key clinical signs: Pointing sign, Rovsing's sign (RLQ pain on LLQ palpation), Psoas sign (retrocaecal appendix), Obturator sign (pelvic appendix).

In appendicitis: Anorexia → pain → vomiting (sequence). In gastroenteritis: vomiting → pain (different sequence).

Never forget: Check hernial orifices, do DRE, examine testes, and in females, consider gynaecological causes (ectopic pregnancy, ovarian torsion, PID). Always do a urine pregnancy test in women of reproductive age.

Hong Kong specifics: Right-sided diverticulitis, TB ileitis, Klebsiella liver abscess, parasitic infections.

Active Recall - RLQ Pain: Definition, Epidemiology, Anatomy, Aetiology, Pathophysiology and Clinical Features

Differential Diagnosis of RLQ Pain

The differential diagnosis of RLQ pain is one of the most clinically tested topics in surgery. The key is to think systematically by organ system, then narrow down using clinical features, demographics, and investigations. Let's build a structured framework from first principles.

Complete Differential Diagnosis Table

Diagnosis	Key Distinguishing Features	Why It Causes RLQ Pain
Acute appendicitis	Classical migratory periumbilical → RLQ pain; anorexia → pain → vomiting sequence; low-grade fever; McBurney's tenderness, Rovsing's/Psoas/Obturator signs ^[1]^[2]^[3]	The appendix base lies at McBurney's point in the RLQ. Transmural inflammation irritates the overlying parietal peritoneum → somatic RLQ pain
Caecal diverticulitis	RLQ pain + fever + leucocytosis; older age group (mean 63 years); right-sided diverticulosis is common in Asia — OFTEN confused with acute appendicitis ^[1]^[6]	Inflamed right-sided diverticulum → pericolic inflammation in the RLQ. No pain migration (unlike appendicitis) because it starts as a localised process from the outset
Cancer of caecum	Insidious onset; may present with iron-deficiency anaemia (chronic occult blood loss from ulcerated tumour surface), palpable RLQ mass, change in bowel habit, or large bowel obstruction ^[4]^[6]	Mass effect and local invasion in the RLQ. Can also cause secondary obstruction of the appendiceal orifice → appendicitis
Ileitis — Crohn's disease	Prolonged diarrhoea ± blood, abdominal pain, weight loss, fatigue, fever; extraintestinal manifestations (mouth ulcers, erythema nodosum, uveitis, arthritis); diarrhoea rather than pain is the predominant symptom ^[1]^[3]	The terminal ileum is the most common site of Crohn's disease → inflammation and thickening of the bowel wall in the RLQ
Ileitis — Yersinia enterocolitica	Yersiniosis characteristically causes RLQ pain; often preceded by gastroenteritis symptoms (diarrhoea, fever); intra-operatively, inflammation occurs around the appendix/terminal ileum with enlarged lymph nodes but the appendix itself is normal ^[3]	Yersinia has a tropism for lymphoid tissue in the terminal ileum and mesenteric lymph nodes → localised RLQ inflammation mimicking appendicitis
Ileitis — Tuberculosis	Ileocaecal TB accounts for ~50% of abdominal TB; systemic features (fever, night sweats, weight loss); RLQ mass (25–50%); CT shows concentric mural thickening in ileocaecal region ± proximal dilatation, adjacent lymphadenopathy ^[7]	TB has a predilection for the ileocaecal region (abundant lymphoid tissue in Peyer's patches → granulomatous inflammation) → RLQ mass and pain. Important in Hong Kong given intermediate TB prevalence
Meckel's diverticulitis	Clinically indistinguishable from appendicitis; small bowel may migrate into RLQ; may have painless PR bleeding (ectopic gastric mucosa → acid secretion → ileal ulceration) ^[1]^[2]	Meckel's diverticulum is located ~2 feet from the ileocaecal valve on the antimesenteric border of the ileum → when inflamed, it lies in or near the RLQ
Mesenteric adenitis	Children and young adults; often preceded by viral URTI or gastroenteritis; fever may be paradoxically higher than appendicitis; shifting tenderness (unlike fixed tenderness in appendicitis) ^[2]^[3]	Reactive enlargement of mesenteric lymph nodes in the ileocaecal region (the terminal ileum mesentery is the richest area of lymphoid tissue in the GI tract) → RLQ pain. Self-limiting
Caecal ischaemia	Elderly patient; risk factors for atherosclerosis or low-flow states; sudden onset cramping abdominal pain; mild-to-moderate rectal bleeding within 24 hours ^[3]	The right colon is supplied by branches of SMA (ileocolic, right colic arteries). Hypoperfusion → mucosal ischaemia → RLQ pain + bloody diarrhoea
Intestinal obstruction	Colicky abdominal pain, vomiting, distension, absolute constipation; previous surgery (adhesions), known hernia, or known malignancy ^[1]^[5]	Any obstructing process affecting the terminal ileum or caecum (adhesions, tumour, volvulus) can cause RLQ pain from bowel distension

Valentino's Sign — A Classic Trap

Perforated peptic ulcer (PPU) can present with RLQ pain. This is called Valentino's sign — named after the silent film actor Rudolph Valentino who died of a perforated duodenal ulcer misdiagnosed as appendicitis. The mechanism: duodenal contents pass along the right paracolic gutter to the RIF → localised peritonism in the RLQ. Clues: sudden onset of pain starting in the epigastrium that passes down the right paracolic gutter; rigidity is usually greater in the RUQ than the RLQ; pneumoperitoneum demonstrable on erect CXR in 70% ^[2]^[3]. Always ask about prior dyspepsia, NSAID use, and do an erect CXR.

In all females of reproductive age presenting with RLQ pain, you MUST take a full gynaecological history (menstrual cycle, vaginal discharge, possibility of pregnancy) and perform a urine pregnancy test ^[3]

Diagnosis	Key Distinguishing Features	Why It Causes RLQ Pain
Ruptured ectopic pregnancy	Amenorrhoea (missed period) + vaginal bleeding (scant, dark) + RLQ pain; positive pregnancy test strongly suggests ectopic if intrauterine pregnancy cannot be visualised; haemodynamic instability; cervical excitation tenderness ^[1]^[3]	A right-sided tubal ectopic ruptures → haemoperitoneum → blood irritates parietal peritoneum in the RLQ and pelvis
Ovarian cyst complications	Sudden onset lower abdominal pain; rupture often begins with strenuous physical activity; torsion is often associated with waves of nausea and vomiting ± fever/leucocytosis (suggests necrosis); particularly painful if dermoid cyst rupture; may be associated with light vaginal bleeding ^[3]	A right ovarian cyst that ruptures or torsions causes localised RLQ/pelvic pain. Torsion → venous congestion → arterial compromise → ischaemia (analogous to testicular torsion)
Pelvic inflammatory disease (PID)	Lower abdominal pain (lower than appendicitis), usually bilateral, exacerbated by coitus (dyspareunia); associated with vaginal discharge, dysmenorrhoea and dysuria; P/E: diffuse lower abdominal tenderness, purulent endocervical discharge, cervical excitation and adnexal tenderness ^[3]	Ascending infection from the cervix to the fallopian tubes → salpingitis → pelvic peritonitis. If predominantly right-sided, can mimic appendicitis
Tubo-ovarian abscess	Complication of PID; inflammatory mass involving ovary, fallopian tube and adjacent pelvic organs; reproductive-age woman; fever, pelvic tenderness, adnexal mass on examination ^[1]	Walled-off pelvic infection forming an abscess → mass effect and inflammation in the RLQ/pelvis
Mittelschmerz	Mid-cycle lower abdominal/pelvic pain due to rupture of follicular cyst and bleeding → irritates peritoneum; self-limiting (hours to 1–2 days); occurs approximately day 14 of the menstrual cycle ^[3]	Ovulation involves rupture of the Graafian follicle → small amount of follicular fluid and blood released into the peritoneal cavity → localised peritoneal irritation
Endometriosis	Chronic/cyclical pelvic pain; dysmenorrhoea, dyspareunia, dyschezia (painful defecation); may cause acute pain during menstruation ^[1]	Ectopic endometrial tissue in the pelvis (right uterosacral ligament, right ovary, pouch of Douglas) undergoes cyclic proliferation and shedding → inflammation and fibrosis → RLQ pain
Acute endometritis	Occurs after obstetrical delivery or invasive uterine procedure; fever, uterine tenderness, purulent lochia ^[1]	Post-procedural infection of the uterus → pelvic inflammation that may lateralise to the RLQ

Diagnosis	Key Distinguishing Features	Why It Causes RLQ Pain
Ureteric colic	Colicky pain typically waxes and wanes, each episode lasting 20–60 minutes; loin-to-groin radiation; patient cannot lie still (writhes); haematuria (micro or macro) ^[3]^[6]	Right ureteric stone (especially at the pelvic brim or VUJ) → ureteric spasm against the obstruction → visceral pain referred to the RLQ. VUJ stones also cause urinary frequency/urgency (stone irritates the detrusor muscle)
Right pyelonephritis	Preceded by irritative urinary symptoms (frequency, urgency); associated with loin tenderness, high fever ( > 39°C), rigors, pyuria ^[3]	Infected right kidney → capsular distension and inflammation → loin/flank pain that may radiate or be felt in the RLQ. The high fever and urinary symptoms differentiate it from appendicitis
Testicular torsion	Sudden onset severe scrotal pain ± radiation to groin and lower abdomen; high-riding horizontal testis; absent cremasteric reflex; nausea/vomiting; pain may be referred to RIF ^[3]^[8]	The testis is innervated by T10 sympathetic afferents (same as the periumbilical region and midgut) → pain from testicular torsion can be referred to the lower abdomen/RLQ. Always examine the scrotum in any male with RLQ pain
Epididymo-orchitis	Storage LUTS + unilateral testicular pain + high fever/rigors; gradual onset (unlike sudden onset in torsion); positive Prehn's sign (elevation of testis relieves pain — opposite of torsion) ^[8]	Infection ascending from the urethra/bladder → epididymal inflammation → scrotal and referred lower abdominal pain
UTI / Cystitis	Dysuria, frequency, urgency, suprapubic pain, turbid urine ^[8]	Bladder inflammation can cause suprapubic and lower abdominal pain that may be lateralised to the RLQ, especially if there is concomitant right ureteric orifice involvement

Diagnosis	Key Distinguishing Features	Why It Causes RLQ Pain
Strangulated inguinal/femoral hernia	Tender, irreducible groin lump; overlying erythema; signs of intestinal obstruction (vomiting, distension, absolute constipation); can cause pain at left and right side ^[4]^[6]	Incarcerated bowel loop within the hernia sac → venous congestion → arterial ischaemia → localised pain. A femoral hernia in an elderly woman is a classic mimic of appendicitis (Richter's hernia may not obstruct)
Rectus sheath haematoma	History of anticoagulation or abdominal wall trauma; tender abdominal wall mass; Fothergill's sign (mass does not cross midline and becomes more prominent on tensing rectus — i.e., the mass is in the abdominal wall, not intra-abdominal)	Rupture of inferior epigastric artery → haematoma within the rectus sheath → localised RLQ pain and tenderness

Diagnosis	Key Distinguishing Features	Why It Causes RLQ Pain
Mesenteric ischaemia (SMA occlusion)	Elderly; atrial fibrillation; "pain out of proportion to examination"; metabolic acidosis; elevated lactate	SMA occlusion → ischaemia of the entire midgut (jejunum, ileum, caecum, ascending colon) → diffuse abdominal pain that may initially be felt in the RLQ before becoming generalised
Ruptured right iliac artery aneurysm	Elderly; known peripheral vascular disease; sudden severe RLQ/flank pain; hypotension; pulsatile mass	Rupture of an aneurysmal right common or internal iliac artery → retroperitoneal haemorrhage → RLQ pain and shock

Diagnosis	Key Distinguishing Features	Why It Causes RLQ Pain
Perforated peptic ulcer (Valentino's sign)	Sudden onset epigastric pain → passes down the right paracolic gutter to the RIF; rigidity usually greater in RUQ than RLQ; pneumoperitoneum on erect CXR in 70% ^[2]^[3]	Duodenal/gastric contents track down the right paracolic gutter (anatomically, the right paracolic gutter is a natural channel for peritoneal fluid to flow from the upper to lower abdomen — it is wider and more continuous than the left)
Right basal pneumonia	Cough, sputum, dyspnoea, pleuritic chest pain; crackles on auscultation of right lower zone; fever	Inflammation of the right lower lobe → irritation of the diaphragmatic pleura → pain referred to the right upper abdomen and occasionally RLQ via the intercostal nerves (T7–T12)
Acute pancreatitis	Epigastric pain radiating to the back; raised amylase/lipase; history of gallstones or alcohol ^[2]	Pancreatic inflammation can be extensive and inflammatory exudate can track along the mesentery to the RLQ. Also, the pain of pancreatitis is sometimes described as shifting from periumbilical to RLQ in early stages ^[5]
Psoas abscess	Fever; flank/back pain; hip held in flexion (flexion deformity); positive psoas sign	Infection (TB, vertebral osteomyelitis) or haematogenous seeding forms an abscess in the psoas muscle → irritation of the iliopsoas → RLQ and flank pain

Differential Diagnosis in Specific Populations

Differential diagnosis of acute abdominal pain in children (the spectrum is different from adults):

Diagnosis	Key Features
Acute appendicitis	Similar to adults but more likely to be complicated (delayed presentation); serial examination is important for clinical diagnosis ^[9]
Mesenteric adenitis	Most common mimic of appendicitis in children; often post-viral
Intussusception	Classically < 2 years; colicky pain + "redcurrant jelly" stools + sausage-shaped mass
Meckel's diverticulitis	Painless PR bleeding or appendicitis-like presentation
Testicular torsion (males)	Always examine the scrotum in a boy with abdominal pain
Henoch-Schönlein purpura (HSP)	Palpable purpura on buttocks/legs + joint pain + abdominal pain (from intramural bowel haematoma) + haematuria ^[9]
DKA	May present with severe abdominal pain mimicking surgical abdomen; check blood glucose
Gastroenteritis	Diarrhoea and vomiting predominate; pain diffuse, not localised

The following features help you distinguish between the major differentials at the bedside:

Discriminator	Significance
Pain migration (periumbilical → RLQ)	Highly suggestive of appendicitis (visceral → somatic pain transition). Ectopic pregnancy pain is characteristically non-migrating ^[3]
Sequence: anorexia → pain → vomiting	Classic for appendicitis. In gastroenteritis, vomiting typically precedes or accompanies pain ^[2]
Diarrhoea as predominant symptom	Suggests infectious colitis, Crohn's disease, or IBD rather than appendicitis (where diarrhoea, if present, is a secondary feature from pelvic appendix irritating the rectum) ^[1]
Vaginal discharge + dyspareunia	PID ^[3]
Missed period + vaginal bleeding	Ectopic pregnancy until proven otherwise ^[1]^[3]
Mid-cycle timing	Mittelschmerz ^[3]
Colicky loin-to-groin pain + haematuria	Ureteric colic ^[3]
High fever ( > 39°C) + rigors + loin tenderness	Pyelonephritis ^[3]
Sudden scrotal pain + high-riding testis	Testicular torsion ^[8]
Tender irreducible groin lump	Strangulated hernia
Epigastric pain → RLQ + pneumoperitoneum	PPU (Valentino's sign) ^[2]^[3]
Chronic symptoms + weight loss + night sweats	TB ileitis or malignancy ^[7]
Painless PR bleeding + elderly	Caecal ischaemia or caecal carcinoma ^[3]

This is the most commonly tested comparison. Here is a side-by-side table:

Feature	Appendicitis	Caecal Diverticulitis	Mesenteric Adenitis	Crohn's Ileitis	Ectopic Pregnancy	PID
Age	10–30	> 50	Children	20–40	Reproductive age	Reproductive age
Pain onset	Gradual, migratory	Gradual, non-migratory	Gradual	Subacute/chronic	Sudden	Gradual
Pain location	Periumbilical → RLQ	RLQ from the start	RLQ (shifting)	RLQ	RLQ/pelvic	Lower abdomen, bilateral
Diarrhoea	Uncommon (unless pelvic appendix)	Possible	Common	Predominant symptom	No	Possible
Fever	Low-grade	Yes	Often higher than appendicitis	Variable	Usually no	Yes
Key distinguishing feature	Anorexia → pain → vomiting	Older age; recurrent episodes; CT differentiates	Post-viral; shifting tenderness; normal appendix on imaging	Chronic diarrhoea; weight loss; extraintestinal features	Missed period; +ve pregnancy test	Vaginal discharge; cervical excitation; dyspareunia
CT/USG clue	Dilated appendix > 6mm, periappendiceal fat stranding	Colonic diverticula + pericolic fat stranding; > 10cm involved; no enlarged LN ^[1]	Enlarged mesenteric LN; normal appendix	Mural thickening of terminal ileum; skip lesions	Free pelvic fluid; empty uterus; adnexal mass	Thickened/fluid-filled tubes; free pelvic fluid

Colorectal Cancer vs Diverticulitis

Both can cause bowel wall thickening on CT. Features suggestive of diverticulitis over CRC include: presence of pericolonic and mesenteric inflammation, involvement of > 10 cm of colon, and absence of enlarged pericolonic lymph nodes on CT. However, CRC can only be excluded with colonoscopy after resolution of acute inflammation ^[1]. This is a critical follow-up step that must not be forgotten.

"ACUTE APPENDIX"

A — Appendicitis

C — Crohn's disease / Caecal diverticulitis / CA caecum

U — Ureteric colic / UTI

T — Testicular torsion / Tubo-ovarian abscess

E — Ectopic pregnancy / Endometriosis

A — Adenitis (mesenteric)

P — PID / PPU (Valentino's sign)

P — Psoas abscess / Pyelonephritis

E — Epididymitis

N — Neoplasm (caecal)

D — Diverticulitis (right-sided)

I — Ischaemic colitis / Intussusception (children)

X — eXtra-abdominal (pneumonia, hernia)

High Yield Summary

Systematic differential of RLQ pain — by system:

GI: Acute appendicitis (most common surgical cause), caecal diverticulitis (common in Asia — mimics appendicitis), Crohn's/TB/Yersinia ileitis, Meckel's diverticulitis, mesenteric adenitis, caecal ischaemia, caecal carcinoma, intestinal obstruction

Gynaecological: Ruptured ectopic pregnancy, ovarian cyst rupture/torsion, PID/tubo-ovarian abscess, Mittelschmerz, endometriosis, acute endometritis

Urological: Ureteric colic, pyelonephritis, testicular torsion, epididymo-orchitis, UTI

Abdominal wall: Strangulated inguinal/femoral hernia, rectus sheath haematoma

Referred/extra-abdominal: PPU (Valentino's sign — duodenal contents track down right paracolic gutter), right basal pneumonia, pancreatitis, psoas abscess

Must-not-miss emergencies: Ruptured ectopic (urine pregnancy test), testicular torsion (examine scrotum), strangulated hernia (check groin), perforated appendicitis (peritoneal signs), mesenteric ischaemia (pain out of proportion)

Key discriminators: Pain migration = appendicitis; non-migrating = ectopic; bilateral lower pain = PID; colicky loin-to-groin = ureteric colic; diarrhoea predominant = Crohn's/infection; mid-cycle = Mittelschmerz; Valentino's sign = PPU tracking down right paracolic gutter

Hong Kong specifics: Right-sided diverticulitis is proportionally much more common; TB ileitis (ileocaecal region in 50% of abdominal TB); always distinguish from CRC (colonoscopy after resolution)

Active Recall - Differential Diagnosis of RLQ Pain

References

^[1] Senior notes: felixlai.md (Acute appendicitis — differential diagnosis; Diverticular disease — differential diagnosis; Ectopic pregnancy and gynaecological differentials; Testicular torsion — differential diagnosis of scrotal pain) ^[2] Senior notes: maxim.md (Acute appendicitis — differential diagnosis, clinical features, and signs; Acute abdomen — RLQ differential map) ^[3] Senior notes: Ryan Ho GI.pdf (p148–151: Acute Appendicitis — differential diagnoses in adults and females; p146: Ischaemic colitis) ^[4] Lecture slides: GC 195. Lower and diffuse abdominal pain RLQ problems; pelvic inflammatory disease; peritonitis and abdominal emergencies.pdf (p5: RLQ causes; p6: LLQ causes; p13: Common causes of lower abdominal pain) ^[5] Senior notes: Ryan Ho Fundamentals.pdf (p276: Abdominal pain — shifting pain description) ^[6] Senior notes: felixlai.md (Diverticular disease — epidemiology, Asian right-sided predominance; Cancer of caecum; Hernia differential) ^[7] Senior notes: Ryan Ho Respiratory.pdf (p78: Abdominal TB — ileocaecal involvement, CT features, RLQ mass) ^[8] Senior notes: Ryan Ho Urogenital.pdf (p233: Testicular torsion — clinical features and signs; p121: Dysuria approach; p130: Haematuria approach) ^[9] Senior notes: maxim.md (p709: Paediatric surgical abdomen — differential diagnosis)

Diagnostic Criteria, Diagnostic Algorithm, and Investigation Modalities for RLQ Pain

Diagnostic Criteria for Acute Appendicitis

Acute appendicitis — the most common cause of RLQ pain — is the diagnosis for which formal scoring systems have been developed. The diagnosis remains essentially clinical ^[1]^[3]^[10], but scoring systems help stratify risk and decide when imaging is needed.

The operative decision should be based on a clinical and laboratory-based scoring system (Alvarado score) ^[1]^[10]

The original Alvarado score uses the mnemonic MANTRELS:

Component	Category	Points
M — Migratory RLQ pain	Symptom	1
A — Anorexia	Symptom	1
N — Nausea or vomiting	Symptom	1
T — Tenderness in RLQ	Sign	2
R — Rebound tenderness in RLQ	Sign	1
E — Elevated temperature ( > 37.5°C)	Lab	1
L — Leukocytosis (WBC > 10 × 10⁹/L)	Lab	2
S — Shift to the left (> 75% neutrophils)	Lab	1
Total		10

Note: The Modified Alvarado Score (MANTREL) drops the "Shift" component (total out of 9 instead of 10) because a manual differential count is not always readily available ^[3]^[10].

Interpretation: ^[1]^[2]^[3]

Score	Interpretation	Action
≥ 7	Strongly predictive of acute appendicitis	Consider surgery ± confirmatory imaging
5–6	Equivocal — appendicitis possible but not certain	Requires imaging: USG or contrast-enhanced CT
≤ 4	Appendicitis can be ruled out with greater certainty	Evaluate for other diagnoses; discharge with safety-netting if clinically well

Why Does This Score Work?

Each component of the Alvarado score captures a specific pathophysiological feature of appendicitis:

Migratory pain = visceral-to-somatic pain transition (T10 → parietal peritoneum)
Anorexia, nausea/vomiting = systemic inflammatory response (cytokine-mediated)
RLQ tenderness = parietal peritoneal irritation (the hallmark)
Rebound tenderness = peritoneal inflammation (peritoneum "rebounds" against inflamed surfaces)
Fever = pyrogen release from the inflammatory cascade
Leucocytosis = bone marrow response to infection/inflammation (demargination + increased production)
Left shift = release of immature neutrophils (bands) indicating acute bacterial infection

The score essentially quantifies "how many features of appendicitis are present" — but it is not diagnostic on its own. A patient can have appendicitis with a low score (e.g., early disease, elderly, immunosuppressed).

Critical Exam Point

A normal WBC count should NOT be used to rule out acute appendicitis ^[3]. Up to 10–20% of patients with confirmed appendicitis have a normal WBC. Conversely, markedly elevated WBC (e.g., > 16 × 10⁹/L) may be suggestive of gangrenous or perforated appendicitis ^[3]. The WBC is a helpful but imperfect marker.

A more modern alternative to Alvarado, used in some centres:

Variable	Points
Vomiting	1
RLQ pain	1
Rebound tenderness (light/medium/strong)	1/2/3
Temperature ≥ 38.5°C	1
WBC 10–14.9 / ≥ 15	1 / 2
Neutrophils 70–84% / ≥ 85%	1 / 2
CRP 10–49 / ≥ 50	1 / 2

Interpretation: 0–4 = low risk; 5–8 = intermediate (image); 9–12 = high risk (surgery). The AIR score incorporates CRP (which Alvarado does not) and is considered to have better discriminative ability.

Diagnostic Criteria for Other Key RLQ Conditions

If the pain is felt to be more RUQ/upper abdominal, the TG13 diagnostic criteria apply ^[3]:

Suspected diagnosis = 1× local sign + 1× systemic sign
Definite diagnosis = 1× local sign + 1× systemic sign + 1× imaging finding

Local Signs	Systemic Signs	Imaging Findings
Murphy's sign (Sens 50–65%, Spec 79–96%)	Fever	Findings characteristic of acute cholecystitis (USG first-line)
RUQ mass/pain/tenderness	Elevated CRP ( > 3 mg/dL)
	Elevated WBC count

Investigation Modalities — Detailed Breakdown

From the lecture slides, investigations for lower abdominal pain include: ^[4]

Bedside tests: urinalysis, pregnancy test
Blood tests: blood count, renal and liver function, amylase, clotting profile, arterial blood gas, type and screen
Imaging: erect CXR, erect and supine AXR, USG, CT, contrast studies
Endoscopy: colonoscopy, upper endoscopy

Let us now go through each in detail.

Test	What It Tells You	Why It Matters
Urine pregnancy test	Detects beta-hCG in urine	Indicated in ALL women of childbearing age ^[1]^[3]^[4]^[5]. A positive result in a woman with RLQ pain = ectopic pregnancy until proven otherwise. False negatives can occur very early (< 2 weeks post-conception)
Urinalysis (dipstick + microscopy)	Haematuria, pyuria, nitrites, leucocyte esterase	Haematuria → ureteric colic (microscopic haematuria in 90% of ureteric stones). Pyuria → UTI or pyelonephritis. Sterile pyuria can occur in appendicitis (inflamed appendix adjacent to ureter/bladder causes reactive pyuria without true UTI) ^[1]^[6]
Temperature	Fever	Low-grade (37.5–38.5°C) → uncomplicated appendicitis. High-grade ( > 39°C) → perforated appendicitis, abscess, pyelonephritis, PID, cholangitis ^[5]
ECG	Rule out cardiac cause	To rule out basal MI which can refer pain to the upper or right abdomen ^[3]^[5]
Capillary blood glucose	Rule out DKA	DKA can cause severe abdominal pain mimicking an acute abdomen (mechanism: gastroparesis, electrolyte disturbance, mesenteric ischaemia from dehydration) ^[5]

Test	Key Findings	Interpretation
CBC (Complete Blood Count)	Leucocytosis with left shift (increased bands)	Suggests acute infection/inflammation. Markedly elevated WBC ( > 16 × 10⁹/L) suggests gangrenous or perforated appendicitis ^[3]. Normal WBC does NOT rule out appendicitis ^[3]. RBC indices may show microcytic anaemia from chronic blood loss (caecal carcinoma) — note that haemodilution takes 48 hours to set in after bleeding ^[3]^[5]
CRP (C-reactive protein)	Elevated	Rises 6–12 hours after onset of inflammation. Useful for serial monitoring. CRP + WBC together: PPV 61.5%, NPV 88.1% for appendicitis ^[3]
LFT (Liver Function Tests)	Mild bilirubin elevation	Mild elevations in serum bilirubin have been noted to be a marker for appendiceal perforation ^[1]. Also helps differentiate hepatobiliary causes (cholecystitis, cholangitis)
RFT (Renal Function Tests)	Urea, creatinine, electrolytes	Assess hydration status (pre-renal AKI from vomiting/third-spacing). HypoK/hypoCl → prolonged vomiting; HypoK/hypoCa → can cause ileus ^[3]^[5]. Creatinine needed to assess suitability for contrast CT scans ^[3]^[5]
Amylase/Lipase	Elevated	Amylase peaks at 6–24 hours; > 1000 U/L (or ≥ 3× ULN for lipase) is diagnostic of acute pancreatitis ^[3]^[5]. May be mildly elevated in appendicitis, intestinal obstruction, or mesenteric ischaemia — but rarely > 3× ULN
Clotting profile + Type and Screen	INR, aPTT; blood group	Prepare for surgery. Identify coagulopathy. Essential in any patient who may need emergency laparotomy
ABG (Arterial Blood Gas) + Lactate	Metabolic acidosis + elevated lactate	Metabolic acidosis with elevated lactate → intestinal ischaemia (anaerobic metabolism in ischaemic bowel) ^[3]^[5]. Metabolic alkalosis → prolonged vomiting. Always check lactate if you suspect mesenteric ischaemia
Glucose	Elevated	Rule out DKA as a medical mimic of acute abdomen ^[5]

Modality	Findings	Interpretation
Erect CXR	Free gas under diaphragm (pneumoperitoneum)	Indicates perforation of a hollow viscus (e.g., PPU, perforated appendicitis — though perforation of the appendix rarely produces visible pneumoperitoneum because the perforation is usually sealed off). Demonstrable in 70% of PPU ^[3]. Also identifies right basal pneumonia as a cause of referred abdominal pain ^[4]^[5]
Supine AXR	Appendicolith (7–15%) — if present, chance of acute appendicitis is up to 90% ^[3]. Radio-opaque stones (90% of urinary stones are radio-opaque; only 15% of gallstones) ^[5]. Proximal dilatation + distal collapse → intestinal obstruction. '3-6-9 rule': SB > 3 cm, LB > 6 cm, caecum > 9 cm ^[3]. Coffee bean sign → sigmoid volvulus. Sentinel loop sign → localised ileus from adjacent inflammation (pancreatitis) ^[3]^[5]	AXR is NOT recommended in the diagnostic workup of suspected appendicitis — it does not change the level of suspicion ^[1]. However, it is indicated to evaluate for other causes of acute abdomen (obstruction, perforation, stones) ^[1]^[4]
Erect AXR	Air-fluid levels ( > 5 = diagnostic of intestinal obstruction) ^[3]^[5]	Useful if obstruction is suspected as the cause of RLQ pain

In children, the lecture slides specifically mention: investigations include leucocytosis, plain XR (rarely), USG, CT (beware of high radiation) ^[11]

USG is the first-line imaging in pregnant women and children ^[1]^[2]^[3]

Aspect	Details
Advantages	No ionising radiation; no IV contrast needed ^[1]. Safe in pregnancy and children. Can assess gynaecological pathology (ovarian cyst, ectopic pregnancy) simultaneously. Can assess gallbladder (cholecystitis), kidneys (hydronephrosis from ureteric stone)
Disadvantages	Lower diagnostic accuracy than CT; higher non-diagnostic rate; operator-dependent; patient-specific limitations (body habitus, discomfort, overlying bowel gas, appendix location) ^[1]
USG findings of appendicitis	Non-compressible appendix with double-wall thickness diameter > 6 mm ^[1]^[2]^[3]. Focal pain over appendix with compression (point tenderness under the probe) ^[1]. Increased echogenicity of inflamed periappendiceal fat ^[1]^[3]. Fluid in RLQ ^[1]^[3]. Presence of appendicolith (posterior acoustic shadowing) ^[1]^[3]
USG for other RLQ diagnoses	Pelvic USG (TAS or TVS): Ectopic pregnancy (empty uterus + adnexal mass ± free fluid), ovarian cyst rupture/torsion (enlarged ovary with absent Doppler flow in torsion). Renal USG: hydronephrosis from ureteric obstruction. Scrotal Doppler USG: decreased testicular flow + whirlpool sign in torsion ^[8]

Imaging of choice by site of pain: ^[6]

Site of Pain Imaging of Choice
RUQ USG
LUQ CT
RLQ CT with IV contrast
LLQ CT with IV contrast
Suprapubic USG (TAS or TVS)

Site of Pain	Imaging of Choice
RUQ	USG
LUQ	CT
RLQ	CT with IV contrast
LLQ	CT with IV contrast
Suprapubic	USG (TAS or TVS)

CT abdomen + pelvis with IV contrast is the imaging of choice for RLQ pain and has the highest diagnostic accuracy and lowest non-diagnostic rate for appendicitis ^[1]^[2]^[3]^[6].

Aspect	Details
Advantages	Highest diagnostic accuracy (Sens ~95%, Spec ~95% for appendicitis) ^[1]^[3]. Identifies complications (abscess, perforation, phlegmon). Identifies alternative diagnoses (diverticulitis, ureteric stone, ovarian pathology, mesenteric ischaemia, caecal carcinoma). Less operator-dependent than USG
Disadvantages	Radiation exposure — contraindicated in pregnancy and relatively contraindicated in infants/children ^[1]. IV contrast contraindicated in renal insufficiency or contrast hypersensitivity ^[1]
CT findings of appendicitis	Enlarged appendiceal AP diameter > 6 mm with an occluded lumen ^[1]^[2]^[3]. Appendiceal wall thickening > 2 mm ^[1]^[3]. Appendiceal wall hyperenhancement ^[2]^[3]. Periappendiceal fat stranding ^[1]^[2]^[3]. Presence of appendicolith ^[1]^[2]^[3]
CT findings of complications	Periappendiceal abscess: rim-enhancing fluid collection. Free fluid in pelvis/abdomen: perforation. Extraluminal gas: perforation. Phlegmon: ill-defined inflammatory mass
CT findings of alternative diagnoses	Diverticulitis: colonic diverticula + bowel wall thickening > 4 mm + pericolonic fat stranding; involvement of > 10 cm of colon + absence of enlarged pericolonic lymph nodes favours diverticulitis over CRC ^[1]. Ureteric stone: high-density focus in the ureter + proximal hydroureter/hydronephrosis + perinephric stranding. Mesenteric adenitis: cluster of enlarged mesenteric lymph nodes + normal appendix. Ischaemic bowel: bowel wall thickening, pneumatosis intestinalis, portal venous gas. Caecal carcinoma: irregular circumferential mass with luminal narrowing and enlarged regional lymph nodes

Aspect	Details
Advantages	No ionising radiation ^[1] — the preferred advanced imaging in pregnancy when USG is inconclusive
Disadvantages	Higher non-diagnostic rate ^[1]; longer acquisition time; less available; more expensive; patient may not tolerate (claustrophobia)
When to use	Pregnant women with equivocal USG; children where CT radiation is a concern and USG is non-diagnostic

Modality	Indication	Key Findings
Doppler USG scrotum	Suspected testicular torsion	Decreased testicular blood flow (decreased Doppler signal, increased resistive index); whirlpool sign (twisted spermatic cord) ^[8]. Sens 69–100%, Spec 77–100%
Cholescintigraphy (HIDA scan)	If cholecystitis is suspected and USG is equivocal	IV ⁹⁹ᵐTc-HIDA is taken up by hepatocytes → excreted into bile → non-filling of GB indicates obstructed cystic duct → acute cholecystitis. Sens 90–97%, Spec 71–90% ^[3]
CT angiography (CTA)	Suspected mesenteric ischaemia	Filling defect in SMA or its branches; bowel wall thickening; pneumatosis; portal venous gas ^[5]
ERCP/MRCP	If obstructive jaundice is suspected alongside RLQ pain	Direct visualisation of CBD stones; biliary dilatation ^[3]

From the lecture slides: endoscopy (colonoscopy, upper endoscopy) is listed as an investigation modality for lower abdominal pain ^[4]

Modality	Indication	Caution
Colonoscopy	Colonoscopy should be performed after resolution of acute inflammation in patients > 40 years old to exclude colorectal cancer ^[2] — this is a critical follow-up step after an episode of diverticulitis or if a caecal mass is suspected	AVOID endoscopy in the acute setting of an acute abdomen — a sealed-off perforation may be opened by gas insufflation during endoscopy ^[6]
Upper endoscopy	Rarely indicated acutely for RLQ pain; may be needed if PPU is suspected and CXR is negative	Same caution regarding insufflation in suspected perforation

Suspected Diagnosis	Key Investigation	Key Finding
Acute appendicitis	CT abdomen/pelvis with IV contrast	Appendix > 6 mm, wall thickening > 2 mm, fat stranding, appendicolith
Ectopic pregnancy	Urine pregnancy test → pelvic USG + serum beta-hCG	Empty uterus + adnexal mass ± free fluid
Ureteric colic	CT KUB (non-contrast)	High-density stone in ureter, proximal hydronephrosis
Testicular torsion	Clinical diagnosis ± Doppler USG scrotum	Decreased flow, whirlpool sign
Caecal diverticulitis	CT abdomen/pelvis with IV contrast	Diverticula + wall thickening + pericolonic fat stranding
Crohn's ileitis	CT/MRI enterography; colonoscopy with biopsy	Terminal ileum mural thickening; skip lesions; non-caseating granulomas on biopsy
Intestinal TB	CT + colonoscopy with biopsy	Ileocaecal thickening + enlarged LN; caseating granulomas, AFB on biopsy
Mesenteric ischaemia	CT angiography + lactate	Filling defect in SMA; elevated lactate; metabolic acidosis
Ovarian torsion	Pelvic USG with Doppler	Enlarged ovary with absent arterial/venous Doppler flow
PID	Clinical (CDC criteria) + pelvic USG	Thickened/fluid-filled tubes; tubo-ovarian abscess
PPU	Erect CXR	Pneumoperitoneum (free gas under diaphragm) — present in 70%
Caecal carcinoma	CT + colonoscopy with biopsy	Irregular caecal mass; luminal narrowing; histology confirms adenocarcinoma

A common concern is: "If I delay surgery to get a CT, will the appendix perforate?"

Delays of hours for investigations do NOT appear to increase the risk of perforation ^[3]. This is important because it justifies obtaining imaging in equivocal cases — the benefit of a correct diagnosis outweighs the minimal risk of a few-hour delay. However, this does NOT apply to patients with frank peritonitis or haemodynamic instability — these patients need resuscitation and emergency surgery, not imaging.

The Negative Appendectomy Rate

The negative appendectomy rate (NAR) can reach up to 15–30% if solely based on clinical criteria, especially in women where gynaecological mimics are common ^[3]. This is precisely why imaging (CT) is recommended in equivocal cases — it reduces the NAR to < 5% while maintaining high sensitivity for appendicitis. The goal is to operate on the right patients while avoiding unnecessary surgery in those with alternative diagnoses.

High Yield Summary

Diagnosis of appendicitis is essentially clinical, refined by the Alvarado/MANTRELS score:

≥ 7 → high probability → surgery ± imaging
5–6 → equivocal → imaging (CT or USG)
≤ 4 → low probability → consider other diagnoses

Key bloods: CBC (leucocytosis, but normal WBC does NOT rule out appendicitis), CRP, amylase/lipase, LFT (bilirubin elevation = marker of perforation), RFT (hydration, contrast suitability), clotting/T+S (surgical preparation), pregnancy test (mandatory in all reproductive-age females)

Imaging of choice for RLQ pain = CT abdomen/pelvis with IV contrast (highest accuracy, lowest non-diagnostic rate). USG first-line in pregnant women and children. MRI as alternative in pregnancy when USG inconclusive.

CT criteria for appendicitis: Appendix diameter > 6 mm, wall thickening > 2 mm, periappendiceal fat stranding, wall hyperenhancement, appendicolith

Erect CXR: Always do to look for pneumoperitoneum (PPU) and right basal pneumonia

AXR: Not recommended for appendicitis workup specifically, but useful for ruling out obstruction (air-fluid levels, 3-6-9 rule) and detecting appendicolith (if present → 90% chance of appendicitis)

Don't forget: Urine pregnancy test (ectopic), urinalysis (stones/UTI), lactate/ABG (ischaemia), glucose (DKA), ECG (MI). Colonoscopy after resolution if > 40 years old (exclude CRC). Avoid endoscopy in the acute abdomen.

Active Recall - Diagnostic Criteria, Algorithm and Investigations for RLQ Pain

References

^[1] Senior notes: felixlai.md (Acute appendicitis — diagnosis: physical examination, Alvarado score, radiological tests, laboratory tests) ^[2] Senior notes: maxim.md (Acute appendicitis — investigations: Alvarado score, imaging, CT findings) ^[3] Senior notes: Ryan Ho GI.pdf (p105: Investigations for acute abdomen; p150: Approach to workup of acute appendicitis, Modified Alvarado score, imaging; p247–248: Acute cholecystitis — TG13 criteria and imaging; p340–341: Acute pancreatitis — diagnostic criteria and imaging) ^[4] Lecture slides: GC 195. Lower and diffuse abdominal pain RLQ problems; pelvic inflammatory disease; peritonitis and abdominal emergencies.pdf (p12: Investigations list) ^[5] Senior notes: Ryan Ho Fundamentals.pdf (p71: Palpation and peritoneal signs; p276: Pain characteristics; p278: Physical examination of acute abdomen; p279: Investigations for acute abdomen) ^[6] Senior notes: maxim.md (p85–87: Acute abdomen — imaging of choice by site, investigations, avoid endoscopy rule) ^[7] Senior notes: Ryan Ho Respiratory.pdf (p78: Abdominal TB — ileocaecal involvement, CT features) ^[8] Senior notes: Ryan Ho Urogenital.pdf (p231: Scrotal examination and USG scrotum; p233: Testicular torsion — Doppler USG findings) ^[10] Senior notes: felixlai.md (Alvarado score interpretation; diagnostic approach) ^[11] Lecture slides: GC 203. The child needs an operation Common emergencies and surgery in childhood.pdf (p41: Acute appendicitis — investigations in children)

Management of RLQ Pain

Resuscitation, NPO, IV fluids, analgesics ^[2]

Step	Action	Rationale
A — Airway	Ensure patent airway	Obtunded patients (septic shock, DKA) may lose airway protection
B — Breathing	Assess respiratory status, give O₂ if needed	Rule out right basal pneumonia as a cause; assess for sepsis-related tachypnoea
C — Circulation	IV access (large bore), IV fluid resuscitation	Patients are often dehydrated from vomiting, reduced oral intake, and third-space fluid loss. Crystalloids (normal saline, Ringer's lactate/Hartmann's solution) ^[1]. K⁺ replacement may be indicated but given cautiously in AKI ^[1]
NPO	Nil per os	Limits further bowel distension; prepares for potential surgery (aspiration risk during anaesthesia)
Analgesia	Pain control with analgesics	Opioids (e.g., morphine, fentanyl) and/or paracetamol. NSAIDs are first-line for ureteric colic ^[12]. The old teaching that "analgesics mask surgical signs" is outdated — adequate pain relief actually improves clinical assessment ^[1]
NG tube	If vomiting or bowel obstruction suspected	Decompression of the stomach; reduce aspiration risk; "drip and suck" ^[1]
Antibiotics	Start empirically if infection suspected	Before theatre; within 60 minutes of incision (see below)
Monitoring	Vital signs, urine output (catheter if unwell), serial abdominal examination	Detect deterioration early (progression to peritonitis, septic shock)

A. Management of Acute Appendicitis (The Prototypical RLQ Emergency)

This is the most important section. The management has three pillars: supportive care, antibiotics, and surgery.

Resuscitation, NPO, IV fluids, analgesics ^[2]

Adequate hydration with IV fluid resuscitation ^[1]
- Paediatric resuscitation bolus = 10–20 mL/kg full-rate ^[1]
- Maintenance fluid therapy using the 4-2-1 rule (Holliday-Segar):

Weight	Rate
1st 10 kg	4 mL/kg/hr (100 mL/kg/day)
2nd 10 kg	2 mL/kg/hr (50 mL/kg/day)
Each additional kg	1 mL/kg/hr (20 mL/kg/day)

Correction of electrolyte abnormalities ^[1]
Close monitoring of vital signs and urine output ^[1]
Pain control with analgesics ^[1] — paracetamol ± opioids (morphine, fentanyl). Do NOT withhold analgesia while awaiting surgical review.

Prophylactic IV antibiotics ^[2]

This is a critical component. The rationale differs depending on the clinical scenario:

Scenario	Antibiotic Indication	Rationale
Pre-operative prophylaxis	Given within a 60-minute "window" before the initial incision ^[1]	Reduces risk of surgical site infection (wound infection, intra-abdominal abscess). The appendix harbours enteric organisms — operating through a contaminated field requires prophylaxis
Non-complicated appendicitis	Continue antibiotics until 24 hours post-op only ^[2]	Once the source is removed and there is no contamination, prolonged antibiotics are unnecessary and increase the risk of antibiotic resistance and C. difficile infection
Complicated appendicitis (abscess, phlegmon, perforation)	Continue antibiotics for 3–7 days post-op ^[2]	Ongoing bacterial contamination and established infection require a therapeutic (not just prophylactic) course
Non-operative management (Ochsner-Sherren)	Full therapeutic course of IV antibiotics	The antibiotics ARE the primary treatment in this scenario

Antibiotic choices: ^[1]^[2]^[3]

Metronidazole AND 3rd-generation cephalosporin (e.g., ceftriaxone + metronidazole) ^[1]^[2]
Alternative: cefoxitin or cefotetan or cefazolin 2g + metronidazole 500mg IV ^[3]

Why metronidazole? "Metro" = metre (measure), "nidazole" = nitroimidazole class. Metronidazole is a nitroimidazole that is selectively activated by anaerobic organisms (they reduce the nitro group → cytotoxic intermediates that damage DNA). Appendicitis involves mixed aerobic-anaerobic flora (E. coli, Bacteroides fragilis, Peptostreptococcus) — metronidazole provides the anaerobic coverage ^[2], while the cephalosporin covers Gram-negative aerobes.

3. Surgical Treatment — Appendicectomy

Laparoscopic appendicectomy is the first-line treatment ^[2]^[3]

This is a critical decision point based on duration of symptoms and clinical status:

	Immediate Surgery	Interval Surgery (Ochsner-Sherren Regimen)
Indications	Present within 72 hours AND fit for surgery ^[2]	Present > 72 hours AND stable with a walled-off appendix mass ^[2]
	Complicated and unstable → consider open surgery ^[2]
Rationale	Early disease is still resectable with minimal adhesions; delay risks perforation in untreated cases	After 72 hours, a walled-off appendix mass means immediate surgery is technically difficult due to adhesions ^[2]. The inflamed tissue planes are obscured, and forced dissection risks injury to the caecum, iliac vessels, and ureter
Approach	Laparoscopic is preferred: ↓ infection risk, ↓ post-op pain, ↓ hospital stay ^[2]^[3]	IV antibiotics (~90% success rate) ± image-guided drainage of abscess ^[2]
	Open: indicated if gross sepsis ^[2]	Laparoscopic appendicectomy 6–8 weeks later ^[2]
Follow-up	Histology of specimen	Colonoscopy if > 40 years old: exclude colorectal cancer ^[2]

Why Interval Appendicectomy?

Clinical rationale for interval appendicectomy ^[1]:

Prevent recurrence of appendicitis — without appendicectomy, recurrence rates are ~20–30%
Exclude neoplasms — especially in older adults: carcinoid tumour, adenocarcinoma, mucinous cystadenoma and cystadenocarcinoma have higher incidence with age ^[1]. A walled-off mass in an elderly patient could be concealing a caecal malignancy

Treatment failure during the Ochsner-Sherren regimen (as evidenced by bowel obstruction, sepsis, persistent pain, fever, or leucocytosis) requires immediate appendicectomy ^[1]. You cannot persist with conservative management if the patient is deteriorating.

Feature	Laparoscopic	Open
Advantages	↓ wound infection, ↓ post-op pain, ↓ duration of hospital stay ^[2]^[3]	↓ intra-abdominal abscess rate, ↓ operative time ^[3]
Disadvantages	Requires general anaesthesia; slightly higher intra-abdominal abscess rate	Larger wound; more post-op pain; longer recovery
Preferred when	First-line in most cases ^[2]^[3]	Gross sepsis; generalised peritonitis; when laparoscopic equipment/expertise unavailable ^[2]

Positioning: Supine ± Trendelenburg and right side up (allows small bowel to fall away from the operative field by gravity) ^[2]

These are high-yield for exams and consent: ^[2]^[3]

Incision	Description	When Used
Lanz incision	Transverse incision ~2 cm below umbilicus, centred on mid-clavicular line	More popular because it follows Langer's lines → more cosmetically pleasing with reduced scarring ^[2]
Gridiron incision	Perpendicular to the line joining ASIS to umbilicus, at McBurney's point (90° to this line)	Classic teaching incision; muscle fibres are split (not cut) layer by layer ^[2]^[3]
Rutherford-Morrison	Extend Gridiron obliquely upwards and laterally	For paracaecal or retrocaecal appendix that is fixed and difficult to deliver ^[2]^[3]
Lower midline	Vertical midline incision	If diagnosis is in doubt (allows full exploration of the abdomen) ^[3]

This is tested in exams — "what do you do if you find a normal appendix?" ^[3]

Finding	Action
Normal appendix	Exclude alternative causes: terminal ileitis, Meckel's diverticulitis, tubo-ovarian causes (females), mesenteric adenitis (children). Still remove the appendix (to avoid diagnostic confusion in future presentations) ^[3]
Cannot find appendix	Mobilise the caecum + trace the taeniae coli to their confluence — the base of the appendix is always at this point ^[3]
Appendicular tumour — Carcinoid	Simple appendicectomy if < 2 cm; right hemicolectomy if > 2 cm ^[3]
Appendiceal adenocarcinoma	Right hemicolectomy — standard ^[3]

These are important "need to know for consent" points ^[2]:

Timing	Complication	Explanation
Immediate	Conversion to open surgery	Adhesions, poor visualisation, unexpected pathology
	Normal appendix found (still removed)	To prevent future diagnostic confusion
	Malignancy found → requiring right hemicolectomy ± stoma	Unexpected carcinoid or adenocarcinoma
	Injury to surrounding organs	Caecum, iliac vessels, ureter, small bowel
	Bleeding	From mesoappendix or appendicular artery stump
Early	Wound infection (5–10%)	Contaminated field (enteric organisms)
	Intra-abdominal/pelvic abscess (spiking fever post-op)	Residual infected fluid/inadequate washout
	Post-operative ileus	Bowel handling + peritoneal inflammation → temporary paralysis
Late	Incisional hernia	Weakness at the incision site
	Adhesions	Any intra-abdominal surgery causes adhesions
	Recurrent/stump appendicitis	Incomplete removal of appendiceal stump

Conservative management can be considered if uncomplicated (no perforation/abscess) and patient is not fit for surgery ^[2]

Aspect	Details
Regimen	Bowel rest (NPO) + IV ceftriaxone + metronidazole ^[2]
Advantages	Shorter duration of disability; lower pain score; lower risk of surgical complications; faster rate of recovery ^[1]
Disadvantages	Risk of progression to complicated appendicitis; risk of recurrent appendicitis; greater risk in elderly and immunocompromised patients; risk of unexpected lesion in appendix (carcinoid, carcinoma) — risk increases with age ^[1]
Recurrence rates	30% in 3 months; 40% in 1 year; 50% in 3 years ^[2]
Key trials	CODA (2020): 10-day antibiotics non-inferior to appendicectomy, but 30% chance of appendicectomy within 90 days, with increased risk if appendicoliths are present ^[2]

Surgery vs Antibiotics — The Verdict

The evidence is evolving. The CODA trial (2020) and APPAC series suggest that antibiotics alone can work in selected, uncomplicated cases. However, surgery remains the gold standard because ^[3]:

Pre-operative imaging cannot reliably distinguish perforated from non-perforated appendicitis
Stratification of who needs surgery vs who doesn't is unsatisfactory
Non-operative treatment is risky for older, immunocompromised, or comorbid patients in whom disease severity is often underestimated
Appendicoliths predict treatment failure with antibiotics alone

Bottom line: Offer surgery to most patients. Reserve antibiotics-only for patients who refuse surgery or are unfit, with clear counselling about recurrence risk.

B. Management of Right-Sided (Caecal) Diverticulitis

The management parallels that of left-sided diverticulitis, stratified by the Hinchey classification ^[1]^[3]:

Required in 15% of acute diverticulitis ^[3]

Indications: ^[3]

Diffuse peritonitis (Hinchey stage 3–4)
Failure of medical treatment in 3–5 days
Chronic diverticulitis
Obstruction (to obtain histology to rule out colorectal cancer)
Fistula

Surgical options: ^[3]

Procedure	Description	When Used
Hartmann's procedure	Resection of the affected segment + end colostomy + closure of rectal stump	Usually the procedure of choice for emergency surgery; reversal is technically difficult and done > 6 months post-op in only ~50–60% ^[3]
Primary anastomosis ± diverting ileostomy	Resection + re-joining of bowel ends ± temporary ileostomy to protect the anastomosis	Advocated in some cases; ↓ length of stay, ↓ cost, ↑ stoma reversal rate but evidence limited ^[3]
Laparoscopic lavage	Washout of the peritoneal cavity without resection	No longer recommended — ↑ intervention rate and ↑ major complications vs resection ^[3]

Management of diverticular bleeding: ^[1]

Fluid resuscitation and blood transfusion
Colonoscopy to identify and treat the bleeding site (adrenaline injection, metallic clips)
Indications for laparotomy and subtotal/total colectomy:
- Haemodynamically unstable despite adequate resuscitation
- Excessive blood transfusion > 6 units
- Frequent rebleeding or persistent bleeding

C. Management of Ureteric Colic

Indications (the "7 Ss"): Symptomatic, Sepsis, Solitary kidney with obstruction, Size > 10 mm, Social reasons (e.g., airline pilot), Stone growth on follow-up, Significant obstruction ^[12]

Stone Location	Modality
Renal < 10 mm	ESWL or RIRS > PCNL
Renal 10–20 mm	ESWL or RIRS or PCNL
Renal > 20 mm	PCNL > RIRS or ESWL
Proximal ureter	ESWL or URS
Distal ureter	URS (ureteroscopy)

ESWL (Extracorporeal Shock Wave Lithotripsy): ^[1]^[12]

Minimally invasive; does not require anaesthesia
Uses high-energy shock waves for stone fragmentation
Contraindications: pregnancy, active UTI/urosepsis, uncontrolled bleeding diathesis, obstruction distal to stone ^[1]
Limitations: poor efficacy in obese patients (long skin-to-stone distance), hard stones (cystine, calcium oxalate monohydrate, brushite), lower pole stones, complex renal anatomy ^[1]

Condition	Management	Key Points
Ruptured ectopic pregnancy	Emergency laparoscopy or laparotomy; salpingectomy (removal of affected tube) or salpingotomy	Haemodynamic resuscitation first; crossmatch blood; gynaecology consultation
Ovarian torsion	Emergency surgical detorsion (laparoscopy preferred); oophorectomy if non-viable	Time-critical — ovarian salvage rate drops with duration of torsion
Testicular torsion	Emergency surgical exploration + detorsion + orchidopexy (bilateral fixation)	Irreversible damage occurs after 6–12 hours of ischaemia ^[8]. Manual detorsion ("open the book" — medial to lateral) can be attempted if theatre is not immediately available but is NOT definitive. Bilateral orchidopexy because the underlying bell-clapper deformity is usually bilateral
Strangulated hernia	Emergency hernia repair; assess bowel viability → resection + primary anastomosis or stoma if non-viable	Assess viability using the "6 Ps": colour (pallor), pulsation, peristalsis, pinch test (bleeding from cut edge), Doppler, and pH ^[1]
PID	IV antibiotics (ceftriaxone + doxycycline + metronidazole); consider drainage of tubo-ovarian abscess if > 4 cm or not responding to antibiotics	Outpatient oral antibiotics if mild; STI screening and contact tracing
Mesenteric adenitis	Conservative: supportive care, analgesia, observation	Self-limiting; no surgery needed. Important to differentiate from appendicitis
Crohn's ileitis	Medical: steroids (acute flare), immunomodulators (azathioprine, methotrexate), biologics (infliximab, adalimumab); surgical resection for complications (stricture, fistula, abscess)	Avoid extensive bowel resection (Crohn's recurs — preserve bowel length). Stricturoplasty preferred over resection for short strictures
Intestinal obstruction	"Drip and suck" (NPO + NG tube + IV fluids); conservative for 48–72 hours if uncomplicated ^[1]; urgent surgery if strangulation, closed-loop, peritonitis ^[1]	Signs of resolution: ↓ distension, ↓ NG output, passage of flatus/stool, resolving AXR ^[1]. Water-soluble contrast (Gastrografin) follow-through is both diagnostic and therapeutic (hyperosmolar → draws fluid into lumen → ↓ oedema → ↑ peristalsis) ^[1]
Ischaemic colitis	Majority resolve with supportive care ^[3]: NPO, IV fluids, broad-spectrum antibiotics; emergency laparotomy for infarction/necrosis/perforation	Resection of ischaemic segments ± primary anastomosis; second-look procedure to assess viability ^[3]

When any surgery for RLQ pathology involves bowel that may be ischaemic (strangulated hernia, mesenteric ischaemia, appendiceal gangrene extending to caecum), you must assess viability before deciding on resection vs conservation ^[1]:

Feature	Viable	Non-Viable
Colour	Dark colour becomes lighter (after release of strangulation)	Dark colour persists
Mesenteric pulsation	Visible pulsation in mesenteric arteries	No detectable pulsation
General appearance	Shiny	Dull and lusterless
Musculature	Firm; peristalsis may be observed	No peristalsis

If non-viable → resect the affected segment with margins of healthy bowel → primary anastomosis (if conditions allow) or stoma (if peritoneal contamination, haemodynamic instability, or malnutrition).

Condition	Antibiotic Regimen	Duration
Uncomplicated appendicitis (pre-op prophylaxis)	Ceftriaxone + metronidazole (or cefazolin + metronidazole)	Pre-op dose → continue 24h post-op ^[2]
Complicated appendicitis (perforation/abscess)	Ceftriaxone + metronidazole	3–7 days post-op ^[2]
Non-operative appendicitis (Ochsner-Sherren)	IV ceftriaxone + metronidazole	Full course until clinical resolution
Uncomplicated diverticulitis (outpatient)	Amoxicillin-clavulanate OR metronidazole + cotrimoxazole OR ciprofloxacin OR moxifloxacin	7–10 days ^[1]
Complicated diverticulitis (inpatient)	Piperacillin-tazobactam OR metronidazole + cephalosporin/fluoroquinolone	10–14 days ^[1]
PID	Ceftriaxone 500 mg IM single dose + doxycycline 100 mg BD × 14 days + metronidazole 400 mg BD × 14 days	As per regimen
Ureteric colic with infection	Broad-spectrum (e.g., ceftriaxone) + urgent decompression (JJ stent or PCN)	Until sepsis resolves; then definitive stone removal

Treatment	Key Contraindications	Reason
CT with IV contrast	Pregnancy; contrast allergy; severe renal impairment	Radiation teratogenicity; anaphylaxis; contrast-induced nephropathy
ESWL	Pregnancy; active UTI/urosepsis; uncontrolled bleeding diathesis; distal obstruction ^[1]^[12]	Shock waves can harm the foetus; infected stone fragments cause sepsis; bleeding risk; fragments cannot pass if there is distal stricture
NSAIDs for renal colic	Severe renal impairment; active GI bleeding; pregnancy (3rd trimester); aspirin-sensitive asthma	NSAIDs reduce renal blood flow (prostaglandin-dependent) → worsen AKI; gastric mucosal injury; premature closure of ductus arteriosus
Laparoscopic surgery	Severe cardiopulmonary compromise (pneumoperitoneum ↓ venous return); uncorrected coagulopathy; diffuse peritonitis (relative — some centres still perform laparoscopic washout)	CO₂ pneumoperitoneum increases intra-abdominal pressure → ↓ venous return → haemodynamic compromise
Colonoscopy in acute setting	Acute abdomen; suspected perforation	Risk of perforation from gas insufflation → a sealed-off perforation may be opened ^[2]^[6]
Manual reduction of strangulated hernia	Evidence of bowel necrosis (peritonitis, sepsis); risk of reduction "en masse" (hernia mass pushed back below fascia but strangulation persists)	Necrotic bowel returned to abdomen → peritonitis; "en masse" reduction is a dangerous false reassurance ^[2]

High Yield Summary

Initial management (universal): Resuscitate (ABCDE), NPO, IV fluids (crystalloids), analgesia, blood tests, urine pregnancy test, NG tube if vomiting/obstruction.

Acute appendicitis management:

Antibiotics: Ceftriaxone + metronidazole (anaerobic + Gram-negative coverage). Pre-op prophylaxis → 24h post-op if uncomplicated; 3–7 days if complicated.
Surgery: Laparoscopic appendicectomy is first-line. Open if gross sepsis or laparoscopy unavailable.
Timing: Within 72h and fit → immediate surgery. After 72h with walled-off mass → Ochsner-Sherren regimen (IV antibiotics ± drainage → interval appendicectomy at 6–8 weeks).
Unexpected findings at surgery: Normal appendix → still remove it; carcinoid < 2 cm → appendicectomy; carcinoid > 2 cm or adenocarcinoma → right hemicolectomy.
Conservative (antibiotics-only): CODA trial supports non-inferiority, but 30% need surgery within 90 days. Higher risk if appendicolith present. Surgery remains gold standard.

Diverticulitis: Uncomplicated → NPO + IV antibiotics; abscess > 4–5 cm → percutaneous drainage; Hinchey 3–4 → emergency surgery (Hartmann's or primary anastomosis ± ileostomy). Always colonoscopy at 6 weeks. Recurrent uncomplicated attacks are no longer an indication for interval colectomy.

Ureteric colic: NSAIDs first-line for pain. Stone ≤ 4 mm → 95% pass spontaneously. MET (tamsulosin) for distal ureteric stones > 5 mm. Urgent decompression (JJ stent or PCN) for urosepsis/worsening renal function. ESWL, PCNL, or URS for definitive removal depending on size and location.

Testicular torsion: Emergency surgical exploration + bilateral orchidopexy. Irreversible after 6–12h.

Key consent risks for appendicectomy: Wound infection (5–10%), intra-abdominal abscess, conversion to open, normal appendix, unexpected malignancy requiring hemicolectomy, organ injury, bleeding, ileus, adhesions, incisional hernia.

Active Recall - Management of RLQ Pain

References

^[1] Senior notes: felixlai.md (Acute appendicitis — supportive treatment, IV fluids, antibiotics, interval appendicectomy, non-operative approach, risks; Diverticular disease — medical and surgical treatment, diverticular bleeding; Urinary stones — ESWL; Intestinal obstruction — supportive and surgical management; Bowel viability assessment) ^[2] Senior notes: maxim.md (Acute appendicitis — management: resuscitation, antibiotics, laparoscopic appendicectomy, immediate vs interval surgery, Ochsner-Sherren regimen, incisions, consent risks, conservative management, CODA trial, recurrence rates; Intestinal obstruction — management principles) ^[3] Senior notes: Ryan Ho GI.pdf (p138–139: Intestinal obstruction management; p147: Ischaemic colitis management; p152: Appendicitis — approach to management, appendicectomy timing, approach, incisions, unexpected findings; p158–159: Diverticulitis — conservative, percutaneous drainage, surgical management) ^[4] Lecture slides: GC 195. Lower and diffuse abdominal pain RLQ problems; pelvic inflammatory disease; peritonitis and abdominal emergencies.pdf (p12: Investigations) ^[5] Senior notes: Ryan Ho Fundamentals.pdf (p279: Investigations for acute abdomen) ^[6] Senior notes: maxim.md (p85–87: Acute abdomen — avoid endoscopy rule; imaging of choice by site) ^[8] Senior notes: Ryan Ho Urogenital.pdf (p233: Testicular torsion — urgent exploration, manual detorsion) ^[12] Senior notes: Ryan Ho Urogenital.pdf (p140–141: Ureteric colic — acute management, MET, definitive stone removal, ESWL, spontaneous passage rates)

Complications of RLQ Pain Conditions

Complications are the natural consequence of disease progression — they represent what happens when the pathological process outlined earlier is not interrupted in time, or when the treatment itself introduces new problems. Understanding complications from first principles means tracing the pathophysiology to its logical endpoint: What happens if the obstruction is not relieved? What happens if the infection is not contained? What happens if the blood supply is not restored?

We will organise this by the major underlying conditions, since the complications are disease-specific.

A. Complications of Acute Appendicitis

Acute appendicitis follows a predictable pathological cascade: obstruction → inflammation → ischaemia → gangrene → perforation → abscess or peritonitis. Each step in this cascade represents a progressively worse complication.

1. Complications of the Disease Itself

Signs of complications: high fever, RLQ mass, imaging shows abscess/phlegmon (inflammatory mass) ^[2]

Phlegmon ("phlegmone" in Greek = inflammation): an ill-defined inflammatory mass of oedematous, inflamed tissue around the appendix — there is no discrete fluid collection, just matted-together bowel loops, omentum, and mesentery
Abscess: a walled-off collection of pus — on CT it appears as a rim-enhancing fluid collection with internal debris

Feature	Phlegmon	Abscess
Nature	Inflammatory mass, no fluid	Walled-off pus collection
CT appearance	Ill-defined soft tissue density	Rim-enhancing fluid collection ± gas
Management	IV antibiotics → interval appendicectomy	Percutaneous drainage + IV antibiotics → interval appendicectomy ^[3]

Abscess locations (post-perforation): may be interloop, paracolic, pelvic, and subphrenic ^[3]

Why pelvic? — a pelvic appendix perforates directly into the pelvis; also, pus tracks downward by gravity to the pouch of Douglas (the most dependent part of the peritoneal cavity in the supine position) Why subphrenic? — infected peritoneal fluid tracks upward along the right paracolic gutter to the subphrenic space (the same anatomical channel that allows PPU contents to reach the RLQ)

These are the complications that arise from the surgery itself — important for consent discussions and post-operative monitoring ^[1]^[2]^[3].

Timing	Complication	Incidence / Detail	Pathophysiological Basis
Early (days 1–7)	Wound infection	5–10% ^[2]^[3]	The appendix harbours mixed enteric flora (usually a mixture of Gram-negative bacilli and anaerobic bacteria, especially Bacteroides spp. and Streptococcus) ^[3]. Despite prophylactic antibiotics, wound contamination can occur during extraction of the inflamed/gangrenous appendix
		Pain and erythema of the wound on post-op day 4 or 5 ^[3]	This timing reflects the 3–5 day incubation period for surgical site infections. The wound becomes red, warm, swollen, and may discharge pus
		Treatment: wound drainage and antibiotics ^[3]	Open the wound, drain pus, send for culture; secondary intention healing or delayed primary closure
Early (days 5–7)	Intra-abdominal/pelvic abscess	~8% ^[3]	Residual infected peritoneal fluid or inadequate washout during surgery. Pus collects in dependent areas (pelvis, subphrenic space, interloop). Presents with spiking fever, malaise, anorexia post-op day 5–7 ^[3]
		Location: interloop, paracolic, pelvic, subphrenic ^[3]	Pus tracks along peritoneal recesses by gravity and anatomical channels
		Treatment: drainage ± laparotomy ^[3]	Percutaneous CT-guided drainage is first-line; laparotomy if not amenable
Early	Post-operative ileus	Expected for 24–72 hours	Bowel handling during surgery → temporary loss of peristalsis (autonomic reflex). Ileus lasting > 4–5 days indicates continuing intra-abdominal sepsis, especially if associated with fever ^[3]
Early	Haemorrhage	Intra-abdominal, abdominal wall haematoma, scrotal haematoma ^[3]	Inadequate ligation of the appendicular artery (end-artery → bleeds freely if not properly secured) or mesoappendix vessels; trocar-site bleeding in laparoscopic approach
Early	Stump complications	Retained faecolith, stump appendicitis, leak, fistula ^[3]	If the appendiceal stump is not adequately ligated or inverted, a faecolith may be retained → ongoing inflammation. Stump necrosis → leak → localised peritonitis or fistula
Early	Enterocutaneous fistula	Uncommon	Results from an intraperitoneal abscess that fistulises to the skin ^[1]. Can also occur from inadvertent bowel injury during surgery or stump leak
Late	Adhesions	Most common late complication	Any intra-abdominal surgery causes adhesions — fibrin bands form between bowel loops and peritoneal surfaces during the healing process → can cause intestinal obstruction (adhesive IO) and chronic pelvic pain in the RIF ^[3]
	Adhesive intestinal obstruction		Fibrous bands constrict or kink bowel loops → mechanical obstruction. Adhesive IO is the most common cause of small bowel obstruction worldwide
Late	Incisional hernia		Weakness at the incision site → herniation of abdominal contents through the defect. More common with open approach (larger wound) and wound infection (impaired healing)
Late	Recurrent/stump appendicitis	Rare	Incomplete removal of the appendiceal stump — residual appendiceal tissue can become inflamed again ^[2]^[3]. Avoided by ensuring complete excision to the caecal base

B. Complications of Acute Diverticulitis

Diverticulitis complicates approximately 25% of patients with diverticulosis. The complications follow logically from the pathophysiology: inflamed diverticulum → contained infection or → uncontained spread.

Inflammation may result in formation of fistula between colon and adjacent organs ^[1]
A fistula forms when the inflammatory process erodes through the wall of two adjacent hollow structures, creating an abnormal communication

Types of fistula (by frequency): ^[1]

Fistula Type	Frequency	Clinical Presentation	Why It Happens
Colovesical fistula	Most common	Pneumaturia (air in urine — gas from colon enters bladder), fecaluria (faecal matter in urine), dysuria/recurrent UTI	Sigmoid colon lies directly anterior to the bladder (especially in males and post-hysterectomy females) → inflammation erodes through both walls
Colovaginal fistula	Second most common	Vaginal passage of faeces and flatus	Especially in post-hysterectomy patients — the uterus normally separates the sigmoid from the vagina; without it, they are in direct contact ^[1]
Colocutaneous fistula	Uncommon	Usually easy to identify — faeculent discharge from abdominal wall	Abscess tracks from the colon through the abdominal wall to the skin
Coloenteric fistula	Uncommon	May be entirely asymptomatic or result in corrosive diarrhoea ^[1]	Communication between inflamed colon and adjacent small bowel

Management of fistula: ^[1]

Control sepsis with antibiotics and drainage
Resection of the affected segment of colon involved with diverticulitis, usually with primary anastomosis
Simple repair of the secondarily involved organ (e.g., primary closure of bladder or vagina)

Pneumaturia Is Pathognomonic

If a patient describes "air bubbles in the urine" (pneumaturia), think colovesical fistula until proven otherwise. The only other cause is a gas-forming UTI (rare, usually in diabetics). In the context of a history of diverticulitis, this is virtually diagnostic.

Condition	Complication	Mechanism
Ureteric colic	Obstructive uropathy / hydronephrosis	Prolonged obstruction → back-pressure → dilatation of renal pelvis and calyces → compression of renal parenchyma → loss of renal function
	Urosepsis	Infected urine behind an obstruction creates a closed infected system → bacteria enter the bloodstream → septic shock. This is a urological emergency — requires urgent decompression (JJ stent or PCN)
	Steinstrasse ("stone street")	After ESWL, multiple fragments can line up in the ureter creating a secondary obstruction
Ruptured ectopic pregnancy	Haemorrhagic shock	Tubal rupture → haemoperitoneum → hypovolaemia → class III/IV shock if not promptly treated
	Tubal loss / subfertility	Salpingectomy (removal of the affected tube) → reduced future fertility, especially if the contralateral tube is damaged
Testicular torsion	Testicular infarction / loss	Arterial compromise lasting > 6–12 hours → irreversible ischaemic necrosis → orchidectomy required
	Subfertility	Loss of a testis → reduced sperm production. Additionally, the ischaemic testis may generate anti-sperm antibodies (blood-testis barrier is breached by ischaemia → immune system encounters sperm antigens → autoimmune response) → can affect the contralateral testis
PID	Tubo-ovarian abscess	Ascending infection → pus collection in the fallopian tube and ovary → walled-off abscess
	Fitz-Hugh-Curtis syndrome	Perihepatitis — inflammation of the liver capsule (Glisson's capsule) from haematogenous or transperitoneal spread of Chlamydia trachomatis or Neisseria gonorrhoeae → RUQ pain + "violin-string" adhesions between liver and anterior abdominal wall
	Chronic pelvic pain / subfertility	Repeated episodes of PID → tubal scarring and adhesions → chronic pain, ectopic pregnancy risk, infertility
Strangulated hernia	Bowel gangrene and perforation	Incarceration → venous congestion → arterial compromise → ischaemia → necrosis → perforation → peritonitis
	Septic shock	Necrotic bowel → bacterial translocation → systemic sepsis
Crohn's ileitis	Stricture → obstruction	Chronic transmural inflammation → fibrosis → luminal narrowing → small bowel obstruction
	Fistula	Transmural inflammation penetrates through to adjacent structures (enteroenteric, enterovesical, enterocutaneous, perianal fistulae)
	Abscess	Transmural inflammation → microperforation → contained abscess (interloop, psoas, pelvic)
Intestinal obstruction	Strangulation	Closed-loop obstruction or volvulus → compromised mesenteric blood supply → ischaemia → gangrene → perforation → peritonitis
	Dehydration and electrolyte imbalance	Vomiting, third-space fluid sequestration, reduced oral intake → hypovolaemia, hypokalaemia, metabolic alkalosis (from vomiting) or metabolic acidosis (from ischaemia)
	Aspiration pneumonia	Vomiting of faeculent material in distal obstruction → aspiration if airway not protected
Ischaemic colitis	Transmural necrosis / gangrene	Prolonged ischaemia ( > 15% of cases) → full-thickness bowel wall death → perforation → peritonitis. Mortality < 5% if non-gangrenous but up to 50–75% if gangrene develops ^[3]
	Stricture	Healing of ischaemic injury with fibrosis → colonic stricture → chronic or subacute obstruction

This is worth highlighting separately because "missed diagnosis" is itself a major source of complications:

Missed Diagnosis	Consequence	Prevention
Ectopic pregnancy missed	Tubal rupture → haemorrhagic shock → death	Urine pregnancy test in ALL females of reproductive age
Testicular torsion missed	Testicular loss (if > 6–12 hours)	Always examine the scrotum in males with RLQ/lower abdominal pain
Strangulated hernia missed	Bowel gangrene → perforation → peritonitis → septic death	Always check both hernial orifices in EVERY patient
Mesenteric ischaemia missed	Bowel infarction → multiorgan failure → death	Check lactate; CT angiography; suspect in elderly with AF and "pain out of proportion"
Caecal carcinoma missed	Delayed cancer diagnosis → advanced stage	Colonoscopy at 6 weeks after resolution of diverticulitis or any RLQ inflammatory episode in patients > 40

Condition	Prognosis
Uncomplicated appendicitis	Mortality < 0.1% with timely appendicectomy
Perforated appendicitis	Mortality ~1–5%; higher at extremes of age
Uncomplicated diverticulitis	70–100% respond to conservative treatment; negligible mortality ^[3]
Complicated diverticulitis	Mortality 0.6–5% ^[3]
Perforated diverticulitis with diffuse peritonitis	Mortality up to 20% ^[3]
Diverticulitis recurrence	~1/3 patients; not associated with increased risk of complications ^[3]
Ischaemic colitis (non-gangrenous)	Mortality < 5% ^[3]
Ischaemic colitis (gangrenous)	Mortality 50–75% ^[3]
Intestinal obstruction (non-strangulated)	Mortality ~2%
Intestinal obstruction (strangulated)	Mortality 10–30%

High Yield Summary

Complications of acute appendicitis (disease):

Gangrenous appendicitis (end-artery thrombosis → full-thickness necrosis)
Perforation (13–20%): walled-off → phlegmon/abscess; not walled-off → generalised peritonitis
Appendiceal abscess: persistent fever + no improvement on antibiotics; locations include pelvic, interloop, paracolic, subphrenic
Pylephlebitis (septic portal vein thrombosis): high fever, rigors, jaundice → liver abscesses; bacteria drain via appendicular vein → portal vein

Post-operative complications of appendicectomy:

Early: wound infection (5–10%, day 4–5), intra-abdominal abscess (~8%, day 5–7, spiking fever), post-op ileus (> 4–5 days = ongoing sepsis), haemorrhage, stump complications, enterocutaneous fistula
Late: adhesions (→ adhesive IO), incisional hernia, stump appendicitis

Complications of diverticulitis:

Abscess (17%), fistula (colovesical most common → pneumaturia, fecaluria), obstruction (partial from inflammation, complete from fibrotic stricture), perforation → generalised peritonitis (mortality up to 20%), diverticular bleeding (painless massive PR bleed, bleeding and diverticulitis rarely co-exist)
Chronic: recurrence in 1/3, chronic pain, diverticular colitis, stricture

Key safety-netting: Always colonoscopy at 6 weeks after diverticulitis (exclude CRC). Always pregnancy test (exclude ectopic). Always examine scrotum (exclude torsion). Always check hernial orifices (exclude strangulation).

Active Recall - Complications of RLQ Pain Conditions

References

^[1] Senior notes: felixlai.md (Acute appendicitis — complications: perforation, risk factors for perforation, pylephlebitis, post-operative complications, enterocutaneous fistula; Diverticular disease — complications: abscess, fistula, obstruction, perforation) ^[2] Senior notes: maxim.md (Acute appendicitis — complications: gangrenous appendicitis, perforation, phlegmon, abscess, peritonitis; post-operative risks for consent: wound infection, intra-abdominal abscess, ileus, adhesions, incisional hernia, stump appendicitis) ^[3] Senior notes: Ryan Ho GI.pdf (p153: Perforated appendix — S/S, post-operative complications: wound infection, intra-abdominal abscess, ileus, stump complications, haemorrhage, adhesions; p158–160: Diverticulitis — prognosis, recurrence, chronic sequelae, diverticular bleeding; p147: Ischaemic colitis — prognosis and mortality)

Rlq Pain

Definition and Overview

Epidemiology

Acute Appendicitis (the prototypical RLQ emergency)

Right-Sided Diverticulitis

Other Key Epidemiological Points

Risk Factors

For Acute Appendicitis (the headline RLQ diagnosis)

For Right-Sided Diverticulitis

For Other RLQ Pathologies

Anatomy and Function

Contents of the Right Lower Quadrant

Appendix — Detailed Anatomy

Nerve Supply and Pain Referral

Three Anatomical Sites of Ureteric Narrowing

Aetiology (Focus on Hong Kong)

Causes of RLQ Pain (Organised by System)

Causes Also Listed in LLQ Slide That Overlap with RLQ [4]

Pathophysiology (By Major Aetiology)

1. Acute Appendicitis

2. Right-Sided (Caecal) Diverticulitis

3. Ureteric Colic

4. Ruptured Ectopic Pregnancy

5. Mesenteric Adenitis

6. Caecal Ischaemia

7. Meckel's Diverticulitis

8. Testicular Torsion

Classification

By Organ System

By Urgency (Surgical vs Non-Surgical)

By Pain Character

Clinical Features

Symptoms

A. Acute Appendicitis (the "must-know" presentation)

B. Caecal Diverticulitis

C. Ureteric Colic

D. Ruptured Ectopic Pregnancy

E. Testicular Torsion

F. Mesenteric Adenitis

G. Meckel's Diverticulitis

Signs

A. Acute Appendicitis — Specific Signs

B. Signs Specific to Other RLQ Conditions

C. Abdominal Examination Framework for RLQ Pain

Summary Table: Key RLQ Differentials — Symptom Comparison

Active Recall - RLQ Pain: Definition, Epidemiology, Anatomy, Aetiology, Pathophysiology and Clinical Features

References

Organising Framework — Think Anatomically

Complete Differential Diagnosis Table

A. Gastrointestinal Causes

B. Gynaecological Causes

C. Urological Causes

D. Abdominal Wall and Hernia

E. Vascular Causes

F. Referred and Extra-Abdominal Causes

Differential Diagnosis in Specific Populations

Children [9]

Adult Females [3]

Elderly

Narrowing the Differential — Clinical Discriminators

Approach to Prioritising the Differential

Differentiating Acute Appendicitis from Its Key Mimics

Mnemonic for RLQ Differential Diagnosis

Active Recall - Differential Diagnosis of RLQ Pain

The Diagnostic Philosophy

Diagnostic Criteria for Acute Appendicitis

A. Alvarado Score (MANTRELS)

B. Combined WBC and CRP for Screening

C. Appendicitis Inflammatory Response (AIR) Score

Diagnostic Criteria for Other Key RLQ Conditions

Acute Pancreatitis (Revised Atlanta Classification, 2013)

Acute Cholecystitis (Tokyo Guidelines 2013)

Testicular Torsion

Diagnostic Algorithm for RLQ Pain

Investigation Modalities — Detailed Breakdown

1. Bedside Tests

2. Blood Tests

3. Imaging — Plain Radiography

4. Imaging — Ultrasound (USG)

5. Imaging — Contrast CT Abdomen and Pelvis