GC194 Intestinal Obstruction Colorectal Cancer
Intestinal obstruction caused by colorectal cancer occurs when a malignant tumor partially or completely occludes the colonic or rectal lumen, preventing the normal passage of intestinal contents and leading to proximal bowel distension, pain, and obstipation.
Intestinal Obstruction & Colorectal Cancer
This lecture (GC 194) is delivered jointly by Surgery (Prof. WL Law), Medicine (Dr. KC Lai), and Clinical Oncology (Prof. JST Sham). It is a core surgical emergency + surgical oncology topic that integrates:
- Intestinal obstruction (IO) — recognising it, classifying it, deciding conservative vs. operative management.
- Colorectal cancer (CRC) — as the most common cause of large bowel obstruction, including its emergency presentation, staging, and surgical/non-surgical treatment.
Why it matters clinically: IO is a common surgical emergency. Missing strangulation or closed-loop obstruction kills patients. CRC presenting as obstruction is already advanced and carries high operative mortality. The lecture systematically walks through the decision tree that every surgical house officer must master.
Clinical Question Framework
The lecture is structured around seven key questions that mirror the decision-making sequence for any patient with suspected IO [1]:
- Does the patient have intestinal obstruction? (Ileus vs. mechanical obstruction)
- What is the site and cause of obstruction? (Small bowel vs. large bowel)
- Is the obstruction simple or strangulated?
- What investigations should be performed?
- Should the patient be treated conservatively, and for how long?
- What are the indications for surgery?
- What are the surgical options?
Core Concepts & Mechanisms (First Principles)
The gut is a tube. Anything that blocks forward flow of contents (mechanical) or stops the tube from squeezing (functional) causes intestinal obstruction. Understanding this dichotomy is the first step.
Mechanical obstruction implies a physical barrier to the aboral progress of intestinal contents. Ileus implies failure of peristalsis to propel the intestinal contents with no mechanical barrier. [1]
Key Distinction: Ileus vs. Mechanical Obstruction
Ileus = the bowel is "stunned" — no physical blockage, just no peristalsis. Think post-operative, peritonitis, metabolic.
Mechanical obstruction = something physically blocks the lumen. The bowel upstream tries harder (increased bowel sounds initially), then eventually fatigues.
Proximal bowel distended with gas and fluid → Hypersecretion and loss of fluid to extracellular space and peritoneal cavity → Bacterial overgrowth → Compromise of blood supply, leading to necrosis and perforation of bowel (accelerated in closed-loop or strangulating obstruction) [1]
Step-by-step mechanism:
- Obstruction point → luminal contents cannot pass distally.
- Gas accumulation — swallowed air + bacterial fermentation. The proximal bowel balloons.
- Fluid sequestration — the bowel wall secretes fluid into the lumen (hypersecretion), and fluid leaks into the peritoneal cavity (third-spacing). This causes dehydration, electrolyte imbalance, and hypovolaemia.
- Bacterial overgrowth — stagnant contents ferment. Bacteria translocate across the weakened bowel wall → systemic sepsis.
- Vascular compromise — the distended bowel wall compresses its own veins first (venous congestion → oedema → arterial compromise → ischaemia → necrosis → perforation). This is strangulation.
- Closed-loop obstruction accelerates this cascade because the trapped segment cannot decompress in either direction (e.g., competent ileocaecal valve with a distal colonic tumour, or a band adhesion trapping a loop of small bowel at two points).
- Reduced oral intake (patient is vomiting and NPO)
- Vomiting → loss of H⁺, Cl⁻, K⁺ → hypochloraemic hypokalaemic metabolic alkalosis (in high SBO)
- Defective intestinal absorption (oedematous wall)
- Transudation of fluid into peritoneal cavity (third-spacing) [2]
Partial vs. complete obstruction; Chronic vs. acute; Simple obstruction — obstruction of lumen, usually at one point only; Strangulating obstruction — blood supply to bowel impaired; Closed-loop obstruction — lumen occlusion in at least 2 points [1]
| Classification | Definition | Clinical Significance |
|---|---|---|
| Partial vs. Complete | Partial: some gas/stool still passes. Complete: absolute constipation and no flatus | Partial may be managed conservatively; complete is more urgent |
| Simple | One obstruction point, blood supply intact | Can try conservative Mx initially |
| Strangulating | Blood supply compromised | Surgical emergency — delay = bowel death |
| Closed-loop | Lumen blocked at ≥2 points | Very high risk of rapid strangulation; the trapped segment has no way to decompress. Surgical emergency |
Closed-Loop Obstruction — Why Is It So Dangerous?
When obstruction occurs at two points (e.g., a band adhesion trapping a loop, or a competent ileocaecal valve with distal colonic obstruction), the trapped segment cannot decompress. Intraluminal pressure rises rapidly → venous compromise → arterial ischaemia → gangrene → perforation. This is why a competent ileocaecal valve + left-sided colonic cancer = surgical emergency.
Paralytic Ileus
Intra-peritoneal: Post-operative, Peritonitis or intra-abdominal abscess, Inflammatory/infective conditions, Intestinal ischaemia [1]
Retroperitoneal: Retroperitoneal haematoma/infection, Aortic/spinal/urological operations, Pancreatitis [1]
Extra-abdominal: Metabolic abnormalities (electrolyte imbalance, sepsis, uraemia, hypothyroidism, lead poisoning, porphyria); Medications (opiates, anticholinergics, antihistamines, catecholamines); Spinal injury and operation [1]
| Category | Examples | Why They Cause Ileus |
|---|---|---|
| Intra-peritoneal | Post-op, peritonitis, abscess, ischaemia | Direct peritoneal irritation → reflex inhibition of gut motility via sympathetic activation |
| Retroperitoneal | Pancreatitis, retroperitoneal haematoma, aortic surgery | Retroperitoneal inflammation/irritation → reflex ileus (the bowel "senses" nearby inflammation via splanchnic nerves) |
| Metabolic | HypoK⁺, uraemia, hypothyroidism, sepsis | Electrolyte derangement impairs smooth muscle contraction; sepsis causes systemic inflammatory mediators that suppress gut motility |
| Drugs | Opiates, anticholinergics | Opiates bind μ-receptors in the myenteric plexus → decreased peristalsis. Anticholinergics block parasympathetic drive |
Abdominal distention; Constipation; Vomiting; Abdominal pain: diffuse, constant and less severe; Sluggish or absent bowel sounds; Clinical features associated with the cause [1]
Key contrast with mechanical obstruction: In ileus, the pain is constant and diffuse (not colicky), and bowel sounds are sluggish or absent (not hyperactive).
Nil by mouth; Intravenous fluid; Nasogastric decompression; Identify and treat the predisposing cause; Monitor and assessment by daily abdominal X-rays and physical examination [1]
Principle: Ileus is managed by treating the underlying cause (e.g., correct hypokalaemia, drain the abscess, stop the offending drug). Supportive care with IV fluids and NG decompression buys time.
Mechanical Bowel Obstruction — Clinical Approach
Colicky abdominal pain; Abdominal distention; Vomiting and nausea; Constipation; Increased bowel sounds; Severity of each symptom depends on the level of obstruction [1]
| Feature | Small Bowel Obstruction (SBO) | Large Bowel Obstruction (LBO) |
|---|---|---|
| Pain | Prominent, colicky, central | Less prominent, may be diffuse |
| Vomiting | Early, profuse (bilious → feculent if late/distal) | Late, feculent (if at all) |
| Distension | Less prominent if proximal SBO; central if distal | Pronounced, peripheral |
| Constipation | Late finding | Early, absolute constipation |
| Bowel sounds | High-pitched, tinkling, hyperactive | May be less dramatic |
Why does level matter? High SBO → early vomiting (the stomach is close by) but minimal distension (little bowel to distend). Low SBO/LBO → more distension, later vomiting, and earlier absolute constipation.
Previous episodes of bowel obstruction; Previous abdominal or pelvic operation; History of cancer or abdominal/pelvic radiation; History of abdominal inflammatory condition [1]
Why each matters:
- Previous surgery → adhesions (commonest cause of SBO)
- Previous cancer → recurrence, peritoneal carcinomatosis, radiation stricture
- Previous IO → adhesions, recurrence of the same pathology
- Inflammatory condition → Crohn's stricture, diverticular stricture
Assessment of vital signs and hydration status; Abdominal examination: Surgical scars, External hernias, Abdominal mass, Peritoneal signs, Auscultation [1]
Never Forget the Hernia Orifices!
A strangulated femoral hernia is a classic exam trap. The elderly thin woman with SBO — always examine the groins. If you miss an incarcerated hernia on examination, the examiner will not forgive you.
Why each sign matters:
- Surgical scars → adhesions
- External hernias → incarceration/strangulation as the cause
- Abdominal mass → tumour, intussusception, phlegmon
- Peritoneal signs (guarding, rebound, rigidity) → strangulation, perforation → needs urgent surgery
- Auscultation → high-pitched bowel sounds = mechanical; absent = ileus or late mechanical with fatigued bowel
Investigations
Complete blood picture; Serum electrolytes; Arterial blood gas; Renal function test; Amylase [1]
| Test | Why |
|---|---|
| CBP | Raised WCC → strangulation, sepsis. Low Hb → chronic bleeding (CRC) |
| Electrolytes | HypoK⁺, hypoNa⁺ from vomiting/third-spacing. HypoK⁺ itself worsens ileus |
| ABG | Metabolic acidosis → ischaemia/sepsis. Metabolic alkalosis → vomiting |
| RFT | Pre-renal AKI from dehydration |
| Amylase | Exclude pancreatitis (can mimic IO). Mildly elevated amylase can also occur in IO itself |
Chest X-ray: Exclude perforation with pneumoperitoneum [1]
Why erect CXR? Free gas under the diaphragm (pneumoperitoneum) = perforation → immediate surgery.
Abdominal X-rays (supine and erect films): Are there dilated bowel loops? Are air fluid levels present in erect film? Any gas in the colon and the level of cut-off? Any evidence of strangulation: thumb printing, pneumatosis cystoides intestinalis, free peritoneal gas? Any massive dilatation of colon? Any air in the biliary tree? [1]
| AXR Feature | Interpretation |
|---|---|
| Dilated SB ( > 3 cm) | SBO |
| Dilated LB ( > 6 cm) or caecum > 9 cm | LBO — caecum > 9 cm = risk of perforation |
| Multiple air-fluid levels (erect) | Mechanical obstruction |
| Gas in colon beyond obstruction | Partial obstruction |
| No gas in colon | Complete obstruction |
| Thumbprinting | Mucosal oedema → ischaemia |
| Pneumatosis cystoides intestinalis | Gas in bowel wall → gangrene |
| Portal venous gas | Gas in intrahepatic portal vein branches → advanced gangrene, grave sign |
| Free peritoneal gas | Perforation |
| Air in biliary tree (pneumobilia) | Gallstone ileus (cholecystoenteric fistula) |
| Coffee bean sign (massively dilated sigmoid arising from pelvis) | Sigmoid volvulus |
What the paired AXRs show: supine film with centrally dilated gas-filled loops and valvulae conniventes crossing the lumen; erect film with step-ladder air–fluid levels — classic small-bowel obstructive pattern. Watch also for pneumobilia / calcified focus when gallstone ileus is on the differential. [1]
CT scan: More sensitive than plain abdominal X-rays; Level of obstruction (transition between dilated and collapsed loop); Lesions (tumor, foreign bodies); Viability of bowel (intravenous contrast) [1]
What the CT montage shows: dilated fluid-filled small-bowel loops clustered around a probable transition / mesenteric kink (arrows) — CT answers level, cause, and viability when plain films only say “obstruction.” [1]
CT is the imaging of choice for intestinal obstruction in most centres. It tells you:
- Transition point — where the dilated bowel meets the collapsed bowel
- Cause — tumour, hernia, adhesion band, volvulus (whirl sign)
- Viability — non-enhancing bowel wall with IV contrast = ischaemia
- Complications — free fluid, free air, portal venous gas
CT scan for colonic obstruction: Intravenous contrast, rectal contrast; Site of obstruction; Mass lesion; Perfusion of bowel wall; Distant disease in case of malignancy [1]
Contrast study: Water-soluble contrast differentiates complete and partial obstruction; ?therapeutic effect. Barium study: Precipitates complete obstruction; Barium peritonitis [1]
Water-Soluble Contrast (Gastrografin) in SBO
In adhesive SBO managed conservatively, giving oral water-soluble contrast (Gastrografin) and doing serial AXRs can:
- Differentiate partial from complete obstruction (if contrast reaches colon = partial → continue conservative Mx)
- Possibly have a therapeutic osmotic effect (draws fluid into the lumen → stimulates peristalsis)
- Reduce operating rate and shorten hospital stay (controversial but supported by some evidence)
Never use barium in suspected obstruction — if there is perforation, barium peritonitis is devastating and almost always fatal.
Intraluminal: Foreign bodies, Gallstones, Bezoars, Worms. Intramural: Tumor (primary or secondary), Strictures (Crohn's disease, radiation, anastomotic, drug induced), Intussusception. Extrinsic: Adhesions, Hernias, Volvulus, Intraperitoneal malignancy [1]
| Category | Causes | Notes |
|---|---|---|
| Intraluminal | Foreign bodies, gallstones, bezoars, worms | Gallstone ileus: look for pneumobilia + SBO on AXR/CT |
| Intramural | Tumour, strictures (Crohn's, radiation, anastomotic, drug), intussusception | In adults, intussusception usually has a pathological lead point (tumour) [1] |
| Extrinsic | Adhesions (most common), hernias, volvulus, intraperitoneal malignancy | Adhesions cause ~60-70% of SBO in Western countries [1][2][3] |
Frequency of SBO Aetiologies
Data from a surgical series (Miller G et al., Am J Surg 2000) cited in the lecture [1]:
| Aetiology | Patients, n (%) | Admissions, n (%) |
|---|---|---|
| Adhesions | 410 (74) | 675 (68) |
| Crohn's disease | 39 (7) | 114 (11) |
| Neoplasm | 25 (5) | 55 (5) |
| Hernia | 12 (2) | 28 (3) |
| Radiation injury | 6 (1) | 12 (1) |
| Combination of above | 20 (4) | 56 (6) |
| Miscellaneous | 40 (7) | 61 (7) |
n = 552 patients; 1,001 admissions. Note the high readmission burden of Crohn's disease (7% of patients but 11% of admissions).
Adhesive obstruction is the most common cause of small bowel obstruction in western countries [1]
Adhesive Obstruction — Deep Dive
Adhesions: Congenital, Post-inflammation, Formed after abdominal surgery [1]
Success rate of non-operative treatment: about 50%. Indications for surgery: Non-responsive to conservative treatment; Clinical features of strangulation [1]
Gentle handling of bowel during surgery; Removal of powder from gloves; ?use saline lavage; Sodium hyaluronate bioresorbable membrane (Seprafilm) [1]
Why these work:
- Peritoneal trauma → fibrin deposition → fibrinous adhesions → fibrous adhesions. Minimising trauma (gentle handling, laparoscopic surgery) and physical barriers (Seprafilm) reduce adhesion formation.
- Glove powder (starch/talc) acts as a foreign body irritant → more adhesions.
Administration of water-soluble contrast: Differentiates partial from complete obstruction; Therapeutic effect?; Reduced operating rate?; Shorten hospital stay [1]
Practical approach: If contrast reaches the colon on a follow-up AXR at 6-24 hours → partial obstruction → safe to continue conservative management. If no contrast in colon → likely complete obstruction → consider surgery.
Management Decisions in SBO
Incarcerated, strangulated hernia; Suspected or proven strangulation; Peritonitis; Pneumoperitoneum; Pneumatosis cystoides intestinalis; Closed-loop obstruction; Volvulus with peritoneal signs [1]
High Yield: Signs of Strangulation
Increased abdominal pain and tenderness; Blood in the vomitus; Fever and increased white cell count; Imaging: Thumbprinting, loss of mucosal pattern, gas within the bowel wall or within intrahepatic branches of the portal vein [1]
If ANY of these are present → do not delay surgery. Strangulated bowel mortality is 10-30% vs. 2% for simple obstruction.
For partial obstruction: Adhesions, Crohn's disease, Radiation stricture, Disseminated malignant disease [1]
Non-operative treatment: Intravenous fluid and electrolytes; Nasogastric decompression; Nutrition when prolonged fasting is anticipated; Frequent monitor of vital signs, abdominal signs and X-rays [1]
Less abdominal distention; Reduction of nasogastric output; Passage of flatus and bowel movement; Resolution in abdominal X-rays; Unresolved obstruction → surgical treatment (duration of conservative treatment controversial, usually 48 hours) [1]
The 48-hour rule: If no improvement after 48 hours of conservative management → operate. But this is a guideline, not absolute — clinical judgement matters. If the patient is deteriorating at any point, don't wait.
Enterolysis (lysis of adhesions and release of constricting bands); Repair of hernia; Foreign bodies (Bezoars, gallstones): Break down and push to colon, or Enterotomy and removal; Bowel resection: Strangulation with gangrenous bowel, Unhealthy bowel [1]
Mortality — Non-strangulating obstruction: 2%; Strangulating obstruction: 10-30% [1]
Colonic Obstruction
About 15% of intestinal obstruction; Usually at sigmoid colon; A lesion at ileocaecal valve presents as small bowel obstruction; Competence of ileocaecal valve determines the clinical features of distal colon obstruction [1]
Competent ileocaecal valve vs. Incompetent ileocaecal valve [1]
| Valve Status | What Happens | Clinical Consequence |
|---|---|---|
| Competent | The valve prevents retrograde decompression into the ileum | Closed-loop obstruction of the entire colon → massive caecal distension → risk of caecal perforation (caecum has the thinnest wall and largest diameter → Laplace's law: wall tension = pressure × radius / wall thickness) |
| Incompetent | Gas and fluid reflux back into the ileum | The small bowel acts as a "decompression buffer" → slower progression, presents more like SBO with distension and vomiting |
Laplace's Law and Caecal Perforation
Wall tension = (Pressure × Radius) / (2 × Wall thickness). The caecum has the largest diameter and thinnest wall in the colon. In a closed-loop obstruction (competent ileocaecal valve + distal colonic obstruction), the caecum is where perforation occurs first. Caecal diameter > 9-12 cm on AXR = imminent perforation.
Obstructing Colorectal Cancer
15-20% of patients with colorectal cancer present with intestinal obstruction. Characteristics: More advanced cancer; Elderly patients with comorbidity; High operative mortality and morbidity; Worse prognosis [1]
Why worse prognosis? Obstruction implies advanced local disease (circumferential involvement), often in elderly patients who are malnourished, dehydrated, and may have unresectable or metastatic disease. Emergency surgery on an unprepared, distended colon has much higher complication rates than elective surgery.
Resuscitation; Diagnosis: Clinical, Abdominal X-rays, CT scan, Sigmoidoscopy/colonoscopy, Contrast enema [1]
Lower gastrointestinal endoscopy: Diagnostic; Therapeutic (decompression in sigmoid volvulus and pseudo-obstruction; stenting); Cautions: avoid excessive insufflation of gas [1]
Why caution with endoscopy in obstruction? Excessive insufflation can over-distend an already compromised bowel → perforation. Use minimal insufflation or CO₂ (absorbed faster than air).
Surgical Options for Obstructing CRC
Operation: Resection — Primary anastomosis or Without anastomosis; Non-resection — Proximal stoma or Bypass [1]
Determinants of procedures: Patient's factors (general condition, nutritional status, haemodynamic status, ?sepsis, condition of remaining bowel); Tumor factors (site — right vs. left vs. rectum, invasion to adjacent structures, ?perforation/contamination); Surgeon's factors (experience in bowel resection and anastomosis in emergency) [1]
Right-sided obstruction (caecum to splenic flexure): Resection and anastomosis if the patient is stable (right or extended right colectomy); Resection without anastomosis if the patient or the bowel condition is not favourable; Non-resection: Stoma or bypass (advanced tumor) [1]
Why is primary anastomosis safer on the right? The ileum has a relatively clean, liquid content and good blood supply. An ileocolic anastomosis heals well even in the emergency setting (lower leak rate than left-sided anastomosis).
Factors to consider: Competence of ileocaecal valve (closed-loop obstruction → perforation); Heavy bacterial and faecal load in proximal colon; Oedematous unhealthy proximal colon; Poor general condition of patient (malignancy, malnutrition, dehydration); Primary anastomosis is risky [1]
Why is left-sided primary anastomosis risky? The proximal colon is loaded with bacteria and faeces, the bowel wall is oedematous and unhealthy, and the patient is often unwell → high risk of anastomotic leak → faecal peritonitis → death.
| Procedure | Description | When to Use |
|---|---|---|
| 3-stage operation | (1) Transverse colostomy → (2) Resection + anastomosis → (3) Closure of colostomy | Not commonly performed today [1]. Historical approach. |
| Hartmann's operation (2-stage) | Resection without anastomosis [1] — resect tumour, close distal rectal stump, bring proximal end as end colostomy | Most common emergency procedure for left-sided obstruction. Safe because no anastomosis in hostile conditions. Stoma reversal later (but many elderly patients never get reversed). |
| Primary resection + anastomosis (1-stage) | Segmental resection with primary anastomosis (requires on-table lavage) OR Subtotal colectomy with ileorectal/ileocolonic anastomosis | For stable patients with experienced surgeon. Subtotal colectomy removes all the faecal-loaded colon and anastomoses clean ileum to distal colon/rectum. |
Prognosis of emergency surgery for colonic obstruction: Mortality more than 10%. Comorbidity. Advanced malignancy. [1]
Non-surgical treatment: Insertion of metallic stent — Made of metal alloys; Self-expanding mechanism; Insert and deploy under endoscopic and/or fluoroscopic guidance; For definitive palliation (unresectable, metastatic disease); As a bridge to surgery [1]
Stenting for colorectal malignancy — Definitive palliation: Avoids surgery, Avoids stoma. As a bridge to surgery: Avoids emergency surgery, Elective operation with bowel preparation, More time to stage the disease, Lower operative mortality and morbidity, Reduces stoma rate [1]
High Yield: Bridge to Surgery with SEMS
Stenting decompresses the obstruction non-operatively → patient can be optimised (hydration, nutrition, bowel prep), disease can be fully staged (CT TAP, MRI if rectal), and surgery can be done electively with much lower mortality and morbidity. This converts a dangerous emergency operation into a planned procedure with higher chance of primary anastomosis and lower stoma rate.
Contraindications for stenting [2]: Very distal rectal tumour (causes tenesmus and pain), closed-loop obstruction (must rule out with CT first as perforation risk → upstaging to T4), suspected perforation.
Colorectal Cancer — Key Points from Lecture + Supporting Sources
- Commonest cancer in Hong Kong (16.5% of all new cancers)
- 2nd leading cause of cancer death in both males and females
-
90% occurs in patients ≥ 50 years old
- M:F = 1.3:1
- Non-modifiable: Age > 50, male
- Modifiable: Central obesity, sedentary lifestyle, high-fat/red-meat diet, low-fibre diet, smoking
- GI: IBD (UC > CD), polyps
- Endocrine: DM, acromegaly
- Family: 25% have FHx; 10% have familial syndrome (FAP, Lynch syndrome)
- Protective: Aspirin/NSAID use
- CIN pathway (85%): Adenoma-carcinoma sequence (APC → KRAS → TP53)
- MSI pathway (15%): Defective mismatch repair → microsatellite instability
- Location: Rectum > sigmoid most common
Right-sided (proximal): present later — tend to bleed (larger calibre, polypoid lesion) → iron deficiency anaemia, dull vague abdominal pain, right-sided mass. Left-sided (distal): present earlier — tend to obstruct (smaller calibre, annular lesion) → change in bowel habits (tenesmus, reduced stool calibre, mucoid stool), hematochezia, intestinal obstruction [2][4]
- Direct: Along bowel wall, to adjacent organs
- Lymphatic: Follows arterial supply
- Haematogenous: Liver (most common — via portal vein), Lung (distal rectal tumour → IVC → lung)
- Transcoelomic: Ovary (Krukenberg), Pouch of Douglas
- Colonoscopy — gold standard for diagnosis + biopsy
- CT TAP — staging (T, N, M)
- MRI pelvis — mandatory for rectal cancer (CRM, T/N staging, neoadjuvant planning)
- CEA — tumour marker for monitoring, not screening
- PET-CT — not routine; useful for recurrence, synchronous tumours
| Stage | Treatment |
|---|---|
| Stage I | Surgery + analysis of ≥12 LN |
| Stage II | Surgery ± adjuvant chemo (for high-risk: T4, LVI, poor histology) |
| Stage III | Surgery + adjuvant chemo (FOLFOX) ± adjuvant RT (rectal only) |
| Stage IV | Chemo ± surgery for isolated liver/lung mets |
Molecular-guided therapy:
- KRAS/NRAS/BRAF mutant → add anti-VEGF (bevacizumab)
- KRAS/NRAS/BRAF wild-type → add anti-EGFR (cetuximab, panitumumab)
The 2020 MCQ Q74 tests exactly this: KRAS testing guides subsequent systemic treatment in metastatic CRC [8].
- Average risk: Start at age 50
- 2-tier system: FIT (faecal immunochemical test) every 2 years → if positive → colonoscopy
- High-risk: Start at 40 or 10 years before earliest affected family member
- First 2 years: Q3m → 3rd year: Q6m → 4-5th year: yearly → > 5 years: remission
- Each visit: CEA, rigid sigmoidoscopy, LFT
- CT TAP/PET-CT yearly
- Colonoscopy: 1 year post-op → 3 years → 5 years → Q5y
Rotation of the colon along the axis formed by its mesentery → Colon obstruction with impairment of circulation → Occurs commonly at sigmoid (65%) or caecum (30%); X-rays: dilated sigmoid (coffee bean sign) [1]
Barium enema: Bird's beak or ace of spade sign [1]
Treatment: Sigmoidoscopic decompression (recurrence: 50%); Surgery (perforation, strangulation or failed decompression) → Resection [1]
Sigmoid volvulus key points:
- Risk factors: Elderly, institutionalised, chronic constipation, psychotropic drug use, high-fibre diet (in endemic areas)
- First-line treatment: Flexible sigmoidoscopy with deflation and insertion of a flatus tube. Recurrence rate ~50% → offer elective sigmoidectomy to prevent recurrence in fit patients.
- Caecal volvulus: Usually requires surgery (right hemicolectomy) — colonoscopic reduction less reliable.
Intussusception in adults: A lesion is usually found as the leading point → Surgery is usually indicated [1]
In children: Usually idiopathic (hypertrophied Peyer's patches post-viral). Managed non-operatively with pneumatic/hydrostatic reduction.
In adults: Always think tumour (polyp, lymphoma, GIST, lipoma) as the lead point → requires formal resection for diagnosis and treatment.
Massive colon dilatation in the absence of mechanical obstruction; Usually associated with bedridden patients with severe extracolonic diseases or trauma; Distended abdomen without pain; X-rays: severe gaseous distention of colon [1]
Management: To exclude mechanical obstruction; Nasogastric tube feeding and enemas; Colonoscopic decompression; Rectal tube decompression; Neostigmine; Caecostomy [1]
Why Neostigmine? It is an acetylcholinesterase inhibitor → increases acetylcholine at parasympathetic nerve endings → stimulates colonic motility. Works in ~80-90% of cases. Give under cardiac monitoring (risk of bradycardia — have atropine ready).
Key danger: Caecal diameter > 12 cm → risk of perforation → decompression urgently needed.
Intestinal obstruction is a common surgical emergency. Management: initial resuscitation followed by determination of the site and cause of obstruction. Decision on surgery and timing of surgery important. High mortality if complications occur. [1]
Common Exam Traps & Discriminators
| Trap | How to Avoid |
|---|---|
| Confusing ileus with mechanical obstruction | Bowel sounds: absent/sluggish = ileus; increased/tinkling = mechanical |
| Forgetting hernia examination in SBO | Always examine groin + any surgical scars |
| Using barium in suspected obstruction | Never use barium if perforation is possible → barium peritonitis. Use water-soluble contrast (Gastrografin) |
| Diagnosing IBS when weight loss is present | Weight loss = red flag for malignancy. IBS does NOT cause weight loss |
| Right vs. left CRC presentation | Right = anaemia + mass + vague pain. Left = obstruction + change in bowel habit + PR bleeding |
| Choosing surgery for sigmoid volvulus as first-line | First-line = sigmoidoscopic decompression + flatus tube. Surgery only if failed or complicated |
| Missing closed-loop obstruction in LBO | Competent ileocaecal valve + distal colonic obstruction = closed-loop → surgical emergency |
| Not knowing Hartmann's operation | Resection without anastomosis + end colostomy + rectal stump closure. Default safe procedure for emergency left-sided obstruction |
| KRAS vs EGFR testing | KRAS = CRC. EGFR mutation testing = lung cancer. Don't mix them up |
| Ogilvie's syndrome vs mechanical LBO | Ogilvie's = no pain (or minimal), bedridden patient, severe extracolonic disease, bowel sounds present. Must exclude mechanical obstruction with CT |
High Yield Summary
-
IO classification
- Mechanical (physical barrier) vs. Ileus (no peristalsis). Mechanical further classified as simple, strangulating, or closed-loop.
-
SBO
- Commonest cause = adhesions (post-surgical). Conservative trial (48h) unless signs of strangulation, peritonitis, closed-loop → urgent surgery. Gastrografin challenge helps differentiate partial from complete.
-
LBO
- Commonest cause = CRC. Competent ileocaecal valve = closed-loop = emergency. Right-sided → primary anastomosis if stable. Left-sided → Hartmann's (safest) or SEMS bridge to elective surgery.
-
Strangulation signs
- Increasing pain/tenderness, fever, raised WCC, bloody vomitus, thumbprinting, pneumatosis, portal venous gas → URGENT SURGERY. Mortality jumps from 2% to 10-30%.
-
CRC presenting as obstruction
- 15-20% of CRC cases. Advanced disease, elderly, high mortality. SEMS can convert emergency to elective surgery.
-
Volvulus
- Sigmoid (65%) — sigmoidoscopic decompression first, surgery if fails. Caecal (30%) — surgery preferred.
-
Ogilvie's syndrome
- Pseudo-obstruction in bedridden patients. Exclude mechanical obstruction first. Neostigmine works in 80-90%.
-
AXR features
- Coffee bean = sigmoid volvulus. Pneumobilia + SBO = gallstone ileus. Thumbprinting = ischaemia. Pneumatosis = gangrene.
-
CRC screening HK
- FIT Q2y from age 50 → colonoscopy if positive.
-
KRAS testing
- guides systemic therapy in metastatic CRC (wild-type → anti-EGFR eligible).
Active Recall - Lecture Notes
[1] Lecture slides: GC 194. Intestinal obstruction colorectal cancer.pdf [2] Senior notes: Maksim Surgery Notes.pdf (Section 4.3 Intestinal obstruction; Colorectal cancer) [3] Senior notes: Ryan Ho GI.pdf (Section 3.3.1 Intestinal Obstruction) [4] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (Colorectal cancer section) [5] Senior notes: Maksim Medicine Notes.pdf (Clinical oncology - Colorectal cancer) [7] Senior notes: Ryan Ho Diagnostic Radiology.pdf (GI Fluoroscopy Studies) [8] Past papers: 2020 Fourth Summative Assessment MCQ paper.pdf (Q74)
GC193 Inguinal And Scrotal Swelling Different Types Of Hernia
Inguinal and scrotal swellings encompass various hernia types—indirect inguinal (through the deep ring), direct inguinal (through the posterior wall of the inguinal canal), and femoral (through the femoral canal)—as well as non-hernia causes such as hydrocele, varicocele, and undescended testis, each distinguished by anatomical location and clinical characteristics.
GC195 Lower And Diffuse Abdominal Pain RLQ Problems; Pelvic Inflammatory Disease; Peritonitis And Abdominal Emergencies
Lower and diffuse abdominal pain encompasses right lower quadrant pathologies such as appendicitis, pelvic inflammatory disease caused by ascending genital tract infection, and peritonitis resulting from inflammation of the peritoneal cavity, all of which may present as acute abdominal emergencies requiring urgent evaluation and management.