GC186 Lower And Diffuse Abdominal Painfresh Blood In Stool
Lower and diffuse abdominal pain accompanied by fresh blood in the stool is a clinical presentation suggesting pathology of the lower gastrointestinal tract, such as colitis, diverticular disease, intussusception, or ischemic bowel, requiring urgent evaluation to identify the underlying cause.
Lower GI Bleeding & Fresh Blood in Stool
Big Idea: This lecture, delivered by Dr. CC Foo (Chief of Colorectal Surgery, HKU), provides a systematic surgical approach to a patient presenting with fresh blood per rectum (PR bleeding) — from initial assessment through to definitive management. It covers three clinical scenarios: (1) intermittent/episodic PR bleeding, (2) acute lower GI bleeding, and (3) GI bleeding of obscure origin. The lecture is highly clinically oriented and maps directly onto SAQ, MCQ, minicase, and OSCE stations. [1]
Learning Objectives (from lecture summary slide):
- Approach to lower GI bleeding [1]
- Common causes of lower GI bleeding [1]
- Initial resuscitation for acute lower GI bleeding [1]
- Role of different investigations [1]
How it fits into exams: Lower GI bleeding is examined as EMQs (matching clinical scenarios to diagnoses), SAQs (approach to investigation, management algorithm), and minicases (emergency resuscitation). Past papers frequently test the distinction between causes by clinical presentation (see Past Paper Questions below). The lecture integrates with GC 179 (perianal disease), GC 194 (colorectal cancer), GC 033 (IBD), and the diverticular disease deck.
1. General Approach — History, Examination, Investigations
The lecture emphasizes four domains of history: severity/duration of bleeding, GI symptoms (abdominal pain, change in bowel habit), anorectal symptoms, and systemic symptoms. [1]
| Domain | What to Ask | Why It Matters |
|---|---|---|
| Severity & duration | How much blood? How long? Clots? | Quantifies blood loss; clots suggest significant volume |
| GI symptoms | Abdominal pain, change in bowel habit | Pain + bleeding = think cancer, IBD, ischaemic bowel; painless = diverticular, angiodysplasia |
| Anorectal symptoms | Straining, pain on defaecation, prolapse, itch | Suggests outlet-type pathology (haemorrhoids, fissure) |
| Systemic symptoms | Weight loss, fever, night sweats, fatigue | Constitutional symptoms raise suspicion for malignancy or IBD |
Additional history points: previous bleeding episodes, previous investigations, significant co-morbid conditions (heart and liver disease), medications (NSAIDs, anticoagulants, antiplatelet agents), social history, and family history. [1]
Why each matters from first principles:
- Previous episodes: Recurrent self-limiting bleeds → diverticular or angiodysplasia. New onset in elderly → think cancer.
- Previous investigations: Avoid duplicating colonoscopies done recently; tells you what's been excluded.
- Heart disease: Determines resuscitation strategy (cautious fluid, avoid overload), and many cardiac patients are on anticoagulants/antiplatelets.
- Liver disease: Coagulopathy worsens bleeding; portal hypertension can cause rectal varices.
- NSAIDs: Cause small bowel ulcers and exacerbate diverticular bleeding by inhibiting platelet COX-1 → impaired primary haemostasis.
- Anticoagulants/antiplatelets: Warfarin, DOACs, aspirin, clopidogrel — must be identified early because stopping or reversing them is part of acute management.
- Family history: CRC screening criteria change with positive FHx (first-degree relative with CRC before age 60 → earlier screening).
Key examination components: haemodynamic status (BP, pulse, respiratory rate), abdominal examination, rectal examination, and proctoscopy. [1]
Haemodynamic status — This is the single most important initial assessment. A patient who is tachycardic and hypotensive has lost significant blood volume (Class III shock ≥ 30% blood volume loss). The shock index (HR/SBP) > 1 indicates haemodynamic instability and triggers the CT angiogram pathway per BSG guidelines. [1]
Abdominal examination — Look for tenderness (peritonitis in ischaemic bowel/perforation), masses (CRC), distension (obstruction), scars (previous surgery → adhesions, stoma sites).
Digital rectal examination (DRE) — Essential and non-negotiable. You are assessing for: palpable rectal mass, stool colour (fresh blood vs melaena vs normal), anal canal pathology (fissure, haemorrhoids, anal cancer), and sphincter tone. [1] [2]
Proctoscopy — Performed at bedside. Allows direct visualization of the anal canal and lower rectum. Can identify internal haemorrhoids (which are above the dentate line and not palpable on DRE), anal fissures, and low rectal tumours. [1]
General investigations: blood tests — haemoglobin and haematocrit, liver and renal function test, coagulation profile, type and screen. [1]
Specific investigations: endoscopy and imaging studies, localization of bleeder, therapeutic interventions. [1]
| Investigation | Purpose | Key Points |
|---|---|---|
| Hb/Hct | Quantify blood loss | May be normal in acute bleed (haemodilution takes time) |
| LFT | Assess liver synthetic function | Coagulopathy in liver disease |
| RFT | Baseline renal function | Pre-contrast assessment; uraemia causes platelet dysfunction |
| Coagulation profile | INR, APTT | Essential if on anticoagulants; guides reversal |
| Type & screen / crossmatch | Blood product preparation | Always in acute bleed; group & save takes ~45 min, crossmatch adds time |
2. Causes of Lower GI Bleeding
The lecture classifies causes into four anatomical groups: Anal, Colorectal, Small bowel, and Upper GI bleeding (as a mimic). [1]
| Anal | Colorectal | Small Bowel | Upper GI |
|---|---|---|---|
| Haemorrhoid | Cancer | Meckel's diverticulum | Can present as PR bleeding if massive |
| Anal fissures | Rectal ulcers | Angiodysplasia, haemangioma | |
| Cancer (anal) | Diverticular bleeding | Small bowel tumour | |
| Angiodysplasia | Small bowel ulcer (NSAID-related) | ||
| Inflammatory bowel disease | Crohn's disease | ||
| Radiation proctitis | Aortoenteric fistula | ||
| Ischaemic bowel | |||
| Infective colitis | |||
| Post-polypectomy bleeding |
High Yield — Upper GI Can Mimic Lower GI Bleeding
~17% of patients with diverticulosis bleed. The mechanism is ruptured vasa rectum. Bleeding is usually from a single diverticulum. Bleeding stops spontaneously in 80–85%. Rebleeding occurs in ~20–30%. Treatment: endoscopic vs surgical resection. [1]
Why from first principles: Diverticula are outpouchings of mucosa and submucosa through the muscular wall at points where the vasa recta (straight arteries) penetrate the bowel wall. These vessels are draped over the dome of the diverticulum, separated from the lumen by only mucosa. Mechanical trauma or mucosal erosion ruptures the vessel → arterial bleeding → often painless and brisk. [1] [4]
- In Asians: Right-sided diverticula are more common than in Western populations, and these have a higher risk of haemorrhage. [4]
- Key clinical point: Diverticular bleeding typically occurs in the absence of diverticulitis (inflammation). These are separate complications. [4]
- Endoscopic treatment: TTS (through-the-scope) endoscopic clips for diverticular bleeding per ACG 2016 guidelines. [1]
Angiodysplasia: elderly patients, ectasia of submucosal vessels, may be associated with vascular malformations, usually in the right colon, stops spontaneously in 85–90%, rebleeding 25–85%. [1]
Why from first principles: Angiodysplasia represents degenerative vascular ectasias — chronic, low-grade obstruction of submucosal veins where they penetrate the muscular layers causes progressive dilation → eventually thin-walled dilated vessels in the submucosa rupture. The right colon (caecum) is the most common site because it has the greatest wall tension (Laplace's law: larger diameter = greater wall tension).
- Associated conditions: Aortic stenosis (Heyde syndrome — acquired von Willebrand disease type 2A from shear stress through stenotic valve), chronic renal failure.
- Endoscopic treatment: Argon plasma coagulation (APC) — preferred because it's non-contact and provides superficial, controlled coagulation. [1]
IBD: usually bloody diarrhoea but not life-threatening. 6–10% with ulcerative colitis have acute lower GI bleed needing emergency surgery (total colectomy). [1]
The key exam point here: most IBD-related bleeding is manageable medically, but a small proportion (6–10% of UC) present with acute severe colitis + massive bleeding requiring emergency total colectomy. This is a surgical emergency. [1] [5]
Radiation damage to rectal mucosa → formation of vascular telangiectasia. Treatments: blood transfusion, sucralfate enema, steroid enema, argon plasma coagulation (APC), radiofrequency ablation (RFA), formalin instillation, laser/infrared, stoma diversion. [1]
Why from first principles: Radiation (commonly for prostate or cervical cancer) damages the microvasculature of the rectal mucosa → chronic ischaemia → neovascularization with fragile telangiectatic vessels that bleed easily. The onset is typically months to years after radiation.
- APC is the most commonly used endoscopic treatment.
- Stoma diversion is reserved for refractory cases — it diverts the faecal stream to allow the rectum to rest, but does not treat the underlying pathology. [1]
Exam Discriminator — Radiation Proctitis vs Rectal Cancer Recurrence
Both can cause PR bleeding after pelvic radiation. Radiation proctitis → diffuse telangiectasias on endoscopy, typically 6–12+ months post-RT. Rectal cancer recurrence → focal mass/ulcer, often > 2 years post-treatment. Always biopsy suspicious lesions.
More common in Asia. In elderly, critically ill, and bedridden patients. Sudden severe painless bleeding ± shock. Bedside proctoscopy may reveal bleeding ulcer. Treatment: packing of adrenaline-soaked gauze, suture plication, endoscopic electrocoagulation. [1]
Clinical pearl: This is a diagnosis to think of in the ICU patient or nursing-home patient who suddenly passes large volumes of fresh blood. The ulcer is often in the lower rectum and can be seen on bedside proctoscopy — no need to rush to colonoscopy. The first-line bedside treatment is adrenaline-soaked gauze packing, which provides both mechanical compression and local vasoconstriction.
Ischaemic colitis typically presents with acute abdominal pain + bloody diarrhoea in elderly patients with cardiovascular risk factors. Watershed areas (splenic flexure = Griffith's point, rectosigmoid junction = Sudeck's point) are most vulnerable. [6]
Key discriminator from the 2024 EMQ: a patient with AF presenting with abdominal pain, distension, absent bowel sounds, and fresh blood on DRE → think mesenteric ischaemia (arterial embolism from AF). [7]
3. Approach to Different Types of Lower GI Bleeding
Three clinical scenarios: (1) Intermittent/episodic PR bleeding, (2) Acute lower GI bleeding, (3) GI bleeding of obscure origin. [1]
3A. Intermittent / Episodic PR Bleeding
Outlet type bleeding is the most common type. Bright red, fresh PR bleeding, not mixed with stool. Majority from benign conditions, > 90%. ~15% of adults experience this. Dribbling or seen on wiping. [1]
Common causes: Haemorrhoid, anal fissures, polyps, proctitis, rectal ulcers, cancers. [1]
Red flags: change of bowel habit, tenesmus, mucus, duration of bleeding, blood mixed with stool, melaena/altered blood/dark red/maroon-coloured, older age ( > 50? or > 40?), constitutional symptoms, family history. [1]
| Red Flag | Why It Suggests Serious Pathology |
|---|---|
| Change of bowel habit | Alternating constipation/diarrhoea = classic for left-sided CRC |
| Tenesmus | Sensation of incomplete evacuation → rectal mass |
| Mucus | Mucus-producing adenocarcinoma or IBD |
| Blood mixed with stool | Blood originating proximal to anal canal (i.e., colonic source, not outlet) |
| Melaena / altered / dark / maroon | Proximal source → slower transit → more haemoglobin degradation |
| Older age ( > 50) | CRC incidence rises sharply after 50 |
| Constitutional symptoms | Weight loss, fever, night sweats → malignancy or IBD |
| Family history | First-degree relative with CRC → 2–3× risk |
DRE and proctoscopy are essential bedside examinations. [1]
Bedside: Proctoscopy. [1]
Laboratory:
Haemoglobin. CEA — low sensitivity (~30% for colorectal cancer). [1]
CEA is not a screening tool. It is most useful for monitoring CRC recurrence after curative resection, not for initial diagnosis. Its sensitivity of only ~30% means 7 out of 10 CRC patients will have a normal CEA. [1]
Imaging:
Double contrast barium enema (DCBE) — becoming obsolete due to its low sensitivity. [1] CT colonography (CTC) — accepted alternative to colonoscopy, useful when colonoscopy is relatively contraindicated, > 90% sensitivity for lesions ≥ 1 cm. [1]
Endoscopy:
Colonoscopy — current gold standard in detecting colonic neoplasm. Needs diet & bowel preparation ± sedation. Chance of perforation ≤ 0.1%. Therapeutic modalities: clipping, electrocoagulation, laser, argon plasma coagulation, sclerotherapy. [1]
Sigmoidoscopy — simpler preparation, can be done without sedation, only up to 60 cm from anal verge, chance of missing proximal pathologies. Observational studies did not find missed proximal cancers for those with 'outlet type bleeding' (Church 1991, Eckardt 2002). Recommended for ≤ 40 outlet type bleeding, normal DRE exam (ASGE). [1]
Faecal Occult Blood Test (FOBT):
Guaiac-based vs immunochemical (FIT). More of a screening tool. Presence of haemorrhoid does not affect prevalence of positive occult blood test (Korkis 1995). [1]
This is important: students often think haemorrhoids cause false-positive FOBTs. The lecture explicitly states that haemorrhoids do NOT significantly affect FOBT positivity rates — so a positive FOBT still warrants further investigation regardless of known haemorrhoids. [1]
This is a key exam table: [1]
| Age | Investigation |
|---|---|
| ≥ 50 | Colonoscopy |
| 40–50 | Sigmoidoscopy or colonoscopy |
| ≤ 40 | Observation if source of bleeding clearly identified. If not, sigmoidoscopy can be offered |
Why Age 50?
CRC incidence increases significantly after age 50 (this is also the standard screening age). In patients > 50 with PR bleeding, even if outlet-type, you must exclude proximal pathology with a full colonoscopy because the pre-test probability of CRC is high enough to justify the procedure's small risks. In younger patients with clear outlet-type bleeding (e.g., visible fissure + typical symptoms), the probability of proximal cancer is very low, so observation is reasonable. [1]
3B. Acute Lower GI Bleeding
Can be massive. Hypotension. Causes include upper GI (10–15%) / small bowel bleeding. Majority ~70% stop spontaneously. Mortality rate 2–4%. [1]
The three pillars: Resuscitation → Localization → Therapeutic intervention (Endoscopic, Angiographic, Surgery). [1]
Large bore IV cannulas, O2 supplement, HaemoCue, baseline blood tests, clotting profile & type and screen, resuscitation with fluids ± blood products, hourly BP monitoring, pulse oximeter, ECG monitor, urinary catheterization, stop anticoagulants or antiplatelet agents. [1]
Why each step:
- Large bore IV (≥ 16G or 14G): Flow rate is proportional to radius⁴ (Poiseuille's law) — wider cannula = faster resuscitation.
- O2: Compensate for reduced oxygen-carrying capacity from blood loss.
- HaemoCue: Bedside Hb estimation — faster than lab results.
- Urinary catheter: Monitor urine output as a surrogate for renal perfusion (target > 0.5 mL/kg/hr).
- Stop anticoagulants/antiplatelets: Removes pharmacological barriers to haemostasis. Consider reversal agents (vitamin K for warfarin, idarucizumab for dabigatran, protamine for heparin).
Colonoscopy: precise localization, minimal preparation, use of bowel prep optional as blood is cathartic (not recommended by ESGE), poor visualization, therapeutic intervention possible. [1]
Early colonoscopy (vs delayed) reduces all-cause mortality, need for surgery, blood transfusion requirements, and hospital stay (meta-analysis of observational studies). [1]
Colonoscopic Interventions by Pathology (ACG 2016):
| Pathology | Colonoscopic Intervention |
|---|---|
| Diverticular bleeding | TTS endoscopic clips |
| Angiodysplasia | Argon plasma coagulation |
| Post-polypectomy bleeding | Mechanical clips or heater probe |
Localization — Imaging Modalities
Need to be actively bleeding at the time of investigation. [1]
This is the critical concept: all imaging modalities for acute GI bleeding require active bleeding at the time of the study to show extravasation. If the bleed has stopped, the study will be negative.
Detects both arterial and venous bleeding. Requires more time (radiotracer preparation, 60–90 min for image acquisition). Not useful in acute massive GI bleeding. Vague localization. Can be repeated for intermittent bleeding. [1]
- Minimum bleeding rate detected: 0.1–0.5 mL/min — more sensitive than angiography for slower bleeds.
- Advantage: Can re-image over 24 hours for intermittent bleeding (the tracer stays in circulation).
- Disadvantage: Poor spatial resolution — tells you the general area but not the precise vessel.
More widely available, non-invasive, more precise. Sensitivity 85.2% & specificity 92.1% (García-Blázquez 2013 meta-analysis). Similar or higher diagnostic yield compared to colonoscopy (Lee 2020, Miyakuni 2020). [1]
BSG Gut 2019: "If a patient is haemodynamically unstable or has a shock index (HR/SBP) > 1 after initial resuscitation and/or active bleeding is suspected, CT angiography provides the fastest and least invasive means to localise the site of blood loss before planning endoscopic or radiological therapy" (strong recommendation). [1]
- Minimum bleeding rate detected: 0.3–0.5 mL/min.
- Key advantage in the acute setting: Fast (available 24/7, takes minutes), non-invasive, identifies the bleeding site precisely for targeted angiographic embolization.
Positive test if extravasation of contrast. Precise localization. Micro-catheter localization. Intra-arterial vasopressin infusion. Embolization with Gelfoam/polyvinyl alcohol/micro-coil, risk of bowel ischaemia ~20% (decreased to 3–4% for super-selective embolization). SMA cannulated first, then IMA & coeliac. Complications: contrast allergy, renal failure, bleeding from puncture site. [1]
- Minimum bleeding rate detected: 0.5–1.0 mL/min — less sensitive than CTA or RBC scan, but has the advantage of being both diagnostic and therapeutic.
- Why SMA first: Most common sources of lower GI bleeding (right colon diverticula, angiodysplasia) are in the SMA territory.
| Modality | Bleeding Rate (mL/min) | Localization Rate (%) |
|---|---|---|
| Colonoscopy | — | 60–97 |
| RBC scan | 0.1–0.5 | 50 |
| Angiogram | 0.5–1.0 | 47 |
| CT angiogram | 0.3–0.5 | 50–86 |
Generally NOT recommended. HALT-IT RCT: IV tranexamic acid increases risks of VTE. No difference in Hb drop, transfusion rates, intervention rates, hospital stay, or mortality from GI bleeding. [1]
Exam Trap — Tranexamic Acid in GI Bleeding
Unlike in trauma (CRASH-2 trial showed benefit), tranexamic acid does NOT improve outcomes in GI bleeding and actually increases VTE risk. The HALT-IT trial is the key reference. Do not recommend it in a GI bleeding SAQ. [1]
Indications: (1) relatively stable patients with persistent bleeding after exhausting endoscopic & radiological interventions, (2) patients who don't respond to initial resuscitation. [1]
Intraoperative steps: consider upper endoscopy first if not been performed, palpation of small bowel (tumour, diverticulum), on-table upper endoscopy and colonoscopy, on-table enteroscopy (diagnostic yield 80–92%), clamping of bowel segments, segmental resection if source identified (rebleeding rate 0–15%), if no source identified and probable colonic cause → subtotal or total colectomy (rebleeding rate 10–20%). [1]
Why subtotal colectomy for unlocalized colonic bleeding: If you cannot identify the exact segment, doing a segmental resection risks leaving the bleeding source behind (high rebleed rate). A subtotal colectomy removes all potential colonic sources and has a lower rebleed rate, though it is a larger operation.
3C. GI Bleeding of Obscure Origin
Definition: bleeding source not readily identified by conventional means (OGD, colonoscopy). Can be overt (visible bleeding) or occult (refractory iron deficiency anaemia, positive occult blood test). [1]
| Category | Causes |
|---|---|
| Vascular | Angiodysplasia, angiomas, Dieulafoy lesion, watermelon stomach, varices, haemosuccus pancreaticus, haemobilia |
| Ulcerative | Peptic ulcer, reflux disease, Cameron ulcers, Crohn's disease |
| Neoplasms | Polyps, lipoma, lymphoma, carcinoid, GIST, primary small bowel carcinoma, metastatic cancer, melanoma |
| Genetic | Osler-Weber-Rendu (HHT), Blue rubber bleb naevus, Gardner's, Hermansky-Pudlak, Klippel-Trenaunay-Weber, NF I/II, Ehlers-Danlos |
| Others | Medications/NSAID, CMV infection, TB infection, Meckel's diverticulum, diverticulosis |
Key terms to understand:
- Dieulafoy lesion: Aberrant large-calibre submucosal artery that erodes through the mucosa without a surrounding ulcer. Classic cause of massive, recurrent GI bleeding.
- Cameron ulcers: Linear erosions at the diaphragmatic hiatus in patients with large hiatal hernias — mechanical trauma from the diaphragmatic crura.
- Watermelon stomach (GAVE): Gastric antral vascular ectasia — rows of red vessels radiating from the pylorus.
- Haemosuccus pancreaticus: Bleeding from the pancreatic duct (usually from pseudoaneurysm of splenic artery eroding into the duct).
- Haemobilia: Bleeding into the biliary tree.
- Aortoenteric fistula: Communication between the aorta and bowel (usually duodenum) — catastrophic bleeding; think of it in patients with previous aortic graft surgery. [1]
After OGD & colonoscopy (may be repeated). Guaiac-based FOB vs FIT. [1]
Small bowel evaluation:
Capsule endoscopy, small bowel enteroscopy (push, single balloon, double balloon), contrast CT, small bowel follow-through, CT/MR enteroclysis, Meckel's scan. [1]
Capsule endoscopy: non-invasive, examines entire length of small bowel, tissue sampling/therapeutic intervention not possible, risk of capsule retention. [1]
- Capsule retention is the main risk — can get stuck at strictures (especially in Crohn's disease). A patency capsule can be swallowed first to test passage.
- MR enterography is now preferred over small bowel follow-through for structural assessment (especially in suspected Crohn's — no radiation). [8]
- Meckel's scan (Tc-99m pertechnetate): detects ectopic gastric mucosa in Meckel's diverticulum — mainly useful in paediatric patients with painless rectal bleeding. [9]
4. Integration with Related Material
- Most common cause of intermittent bright red PR bleeding
- Internal haemorrhoids: above dentate line, painless bleeding
- External haemorrhoids: below dentate line, painful if thrombosed
- Graded I–IV based on degree of prolapse
- Treatment: rubber band ligation (Grade II–III), haemorrhoidectomy (Grade III–IV) [10]
- Left-sided: change in bowel habit, obstruction, PR bleeding
- Right-sided: iron deficiency anaemia (occult blood loss), mass, less likely to obstruct (larger calibre, liquid stool)
- Staging by TNM; Duke's classification still referenced in exams
- Surgery (segmental resection with lymph node clearance) is mainstay; adjuvant chemotherapy for Stage III [11]
- Diverticulosis → asymptomatic in most; complications = bleeding, diverticulitis, perforation
- Diverticulitis: LLQ pain + fever + leucocytosis; CT is the investigation of choice
- Bleeding and diverticulitis are typically separate complications [13]
5. Exam Intelligence
| Trap | Correct Thinking |
|---|---|
| Assuming all PR bleeding is lower GI | 10–15% of "lower GI bleeds" are actually upper GI |
| Using CEA to screen for CRC | CEA sensitivity is only ~30% — it's a monitoring, not screening, tool |
| Recommending tranexamic acid for GI bleeding | HALT-IT trial showed increased VTE risk; NOT recommended |
| Thinking haemorrhoids cause false-positive FOBT | Korkis 1995: haemorrhoids do NOT affect FOBT positivity |
| Ordering barium enema for workup | Obsolete — use colonoscopy or CTC |
| Assuming all young patients with PR bleeding need colonoscopy | Age ≤ 40 with outlet-type bleeding + no red flags → observation if source identified |
| Confusing diverticular bleeding with diverticulitis | Diverticular bleeding is painless; diverticulitis presents with LLQ pain + fever — separate complications |
| Using RBC scan in massive acute bleed | Takes 60–90 min → too slow; use CTA instead |
| Scenario | Most Likely Diagnosis | Key Discriminator |
|---|---|---|
| Fresh blood dribbling after defaecation, self-limiting, young patient | Haemorrhoid | Outlet-type, painless, post-defaecation |
| Painful defaecation + fresh blood on wiping | Anal fissure | Pain on defaecation is the key distinguishing feature |
| Bloody diarrhoea + mucus + raised inflammatory markers + young | Inflammatory bowel disease | Chronic, systemic inflammation |
| PR bleeding after pelvic radiotherapy, not related to defaecation | Radiation proctitis | History of RT, not defaecation-related |
| Massive sudden PR bleeding with clots + hypotension + elderly | Diverticular bleeding | Painless, massive, self-limiting in majority |
| Elderly + AF + abdominal pain + absent bowel sounds + PR blood | Mesenteric ischaemia / ischaemic colitis | AF = embolic source, pain out of proportion |
| PR bleeding + weight loss + altered bowel habit + older age | Colorectal cancer | Red flags + constitutional symptoms |
6. Past Paper Questions
Q14: A 55-year-old man has noticed fresh blood dribbling into the toilet bowl after defaecation. The bleeding stops spontaneously. This has happened for 4 days in a row.
- Answer: E. Haemorrhoid
- Rationale: Classic outlet-type bleeding — fresh blood, post-defaecation, self-limiting, dribbling. Age 55 warrants colonoscopy to exclude proximal pathology, but the most likely diagnosis is haemorrhoid.
Q15: A 29-year-old man complains of loose stool and lower abdominal pain in the recent 6 months. There is blood and mucus in the stool. He used to have bowel opening once a day but now it is 4 to 6 times a day. His CRP and ESR are raised.
- Answer: F. Inflammatory bowel disease
- Rationale: Young patient, chronic bloody diarrhoea with mucus, increased frequency, raised inflammatory markers. Classic UC presentation. Discriminator vs IBS: raised CRP/ESR (IBS has normal inflammatory markers).
Q16: A 79-year-old man complains of fresh PR bleeding for 6 months. The bleeding is not related to defaecation. He has prostate cancer and had radiotherapy 1 year ago. He is anaemic.
- Answer: I. Radiation proctitis
- Rationale: PR bleeding post-pelvic radiotherapy, not related to defaecation (distinguishes from haemorrhoid), chronic → anaemia. Radiation proctitis develops months to years after RT.
Q17: An 89-year-old man complains of PR bleeding for 1 day. He passes fresh blood clots. He has tachycardia and hypotension. He is pale.
- Answer: D. Diverticular bleeding
- Rationale: Acute massive PR bleeding with haemodynamic instability in elderly. The most common cause of massive lower GI bleeding is diverticular disease. Painless (no mention of abdominal pain). Trap: G (ischaemic colitis) would present with abdominal pain + bloody diarrhoea.
Q18: A 66-year-old lady with known AF presented with abdominal pain and distension. Abdomen diffusely tender, bowel sound absent. DRE revealed fresh blood in anus.
- Answer: G. Mesenteric ischaemia
- Rationale: AF → embolic source → SMA embolism → acute mesenteric ischaemia. Pain + absent bowel sounds + PR blood + AF. Discriminator: absent bowel sounds (paralytic phase) + AF differentiates from simple IO.
Q20: A 60-year-old lady with 2-month history of painless fresh PR bleeding associated with on-and-off constipation. Last BO 1 week ago. Severe weight loss.
- Answer: A. Colorectal cancer
- Rationale: PR bleeding + constipation + significant weight loss in elderly → CRC until proven otherwise. The weight loss is the key red flag.
Q32: A 20-year-old man presented with recurrent perianal abscess in the past few years. Increasing abdominal pain and weight loss. Mild tenderness RLQ and perianal fistula.
- Answer: A. Crohn disease
- Rationale: Recurrent perianal disease (abscess + fistula) + RLQ tenderness (terminal ileum) + weight loss in a young patient. Classic Crohn's presentation. Discriminator: UC does NOT typically cause perianal fistulae.
Q44: An 18-year-old girl with recurrent abdominal pain, diarrhoea for 1 year, 5 kg weight loss, mild RLQ tenderness, perianal skin tags. Colonoscopy: multiple ulcerations in terminal ileum and caecum. What is the best small bowel examination?
- Answer: C. MR enterography
- Rationale: Young patient likely Crohn's disease — MR enterography is the preferred small bowel imaging (no radiation, excellent soft tissue detail). CT enterography (option A) involves radiation. Capsule endoscopy (option D) risks retention in stricturing Crohn's. Faecal calprotectin (option B) is not an imaging modality.
Q57: A 70-year-old man with acute lower abdominal pain, LLQ tenderness + guarding + fever. CT: sigmoid diverticulitis, mesenteric stranding, small gas pockets, 5 cm pelvic abscess. On IV antibiotics. What is the most appropriate next management?
- Answer: D. Radiological guided drainage of abscess
- Rationale: Complicated diverticulitis with 5 cm abscess (Hinchey Ib/II). Abscesses > 3–4 cm require percutaneous drainage. Emergency surgery (option B) reserved for free perforation/peritonitis. Colonoscopy (option A) contraindicated in acute diverticulitis.
Q12: 62-year-old male, 3-month intermittent abdominal pain, alternating constipation/diarrhoea, occasional blood in stool, 10 lb weight loss, hypertension, diabetes, ex-smoker. LLQ tenderness, DRE: palpable mass.
- (a) Most likely diagnosis: Colorectal cancer (rectal cancer given DRE-palpable mass). Hereditary RF: FAP, Lynch syndrome (HNPCC). Environmental RF: smoking, processed/red meat diet, obesity, low fibre.
- (b) Diagnostic investigation: Colonoscopy with biopsy
- (c) Palliative treatments: Self-expanding metallic stent (for obstruction), palliative chemotherapy/RT, defunctioning stoma, palliative resection.
Q6: 65-year-old man, sudden abdominal + back pain, BP 90/40, HR 110, tender expansile central abdominal mass → post-op Day 1 has blood-stained stool + mucus PR.
- (d) Working diagnosis: Ischaemic colitis (post-aortic surgery)
- (e) Confirm: Sigmoidoscopy/colonoscopy (to visualize colonic mucosa)
- (f) Risk factors: Aortic surgery (IMA ligation), hypotension/shock, atherosclerosis, post-operative state
| Step | Intermittent PR Bleed | Acute Lower GI Bleed | Obscure GI Bleed |
|---|---|---|---|
| Priority | Exclude sinister cause | Resuscitate first | Systematic small bowel evaluation |
| Key history | Red flags, outlet vs proximal | Volume, haemodynamic status, meds | Recurrent anaemia, FOBT+ |
| Examination | DRE + proctoscopy | Haemodynamics + DRE | DRE, look for vascular lesions |
| First investigation | Age-based: colonoscopy vs sigmoidoscopy | CTA if shock index > 1; colonoscopy if stable | Repeat OGD + colonoscopy |
| Next steps | Biopsy any lesion found | Endoscopic therapy → angiography → surgery | Capsule endoscopy → enteroscopy |
| When to operate | Cancer confirmed → staged resection | Failed endoscopic/radiological Rx; uncontrolled bleeding | Localized source → segmental resection |
High Yield Summary
Lower GI bleeding is classified into intermittent/episodic, acute, and obscure. The most common causes are haemorrhoids (intermittent), diverticular bleeding (acute massive), and angiodysplasia (elderly, right colon). Always exclude upper GI source (10–15% of "lower" bleeds). For intermittent bleeding, investigate based on age and red flags. For acute bleeding, resuscitate first (large bore IV, O2, fluids, stop anticoagulants), then localize with CTA if haemodynamically unstable (shock index > 1) or colonoscopy if stable. Colonoscopic therapies: clips for diverticular, APC for angiodysplasia, clips/heater probe for post-polypectomy. Tranexamic acid is NOT recommended (HALT-IT trial). For obscure bleeding, capsule endoscopy is the first-line small bowel investigation. Surgery (subtotal colectomy) is the last resort when the source cannot be localized. CEA sensitivity for CRC is only ~30% — use colonoscopy for diagnosis. Haemorrhoids do NOT cause false-positive FOBT.
Active Recall - Lecture Notes
[1] Lecture slides: GC 186. Lower and diffuse abdominal painfresh blood in stool.pdf [2] Lecture slides: Clinical Demonstration_Abdomen.pdf [3] Senior notes: Block A - Coffee ground vomitus tarry stool upper GI bleeding.pdf [4] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (Lower GI bleeding section) [5] Lecture slides: GC 033. Chronic diarrhea_irritable bowel syndrome and inflammatory bowel disease.pdf [6] Senior notes: Maksim Surgery Notes.pdf (Ischemic bowel disease section) [7] Past papers: 2023 Fourth Summative MCQ.pdf (EMQ Section V, Q17-20) [8] Past papers: 2021 Fourth Summative Assessment MCQ.pdf (Q44) [9] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Meckel's diverticulum section) [10] Lecture slides: GC 179. Anal pain perianal lesions and sepsis.pdf [11] Lecture slides: GC 194. Intestinal obstruction colorectal cancer.pdf [12] Senior notes: Block A - Chronic diarrhoea_ irritable bowel syndrome and inflammatory bowel disease.pdf [13] Lecture slides: Diverticular diseases - Dr. J Tsang.pdf [14] Past papers: 2024 Fourth Summative MCQ.pdf (EMQ Section IV: Per Rectal Bleeding, Q14-17) [15] Past papers: 2020 Fourth Summative Assessment MCQ paper.pdf (Q32) [16] Past papers: 2025 Fourth Summative MCQ.pdf (Q57) [17] Past papers: 2025 Fourth Summative SAQ.pdf (Q12) [18] Past papers: 2017 Fourth Summative SAQ.pdf (Q6)
GC185 Feed Him Up Before Surgery Surgical Nutrition, Enteral And Parenteral Feeding
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