By MRCSA in MRCS Part A — 04 Jul 2026

52 COLORECTAL SURGERY

# COLORECTAL SURGERY

Colorectal surgery is one of the most heavily examined territories in MRCS Part A. Questions cluster around blood supply (which artery to ligate, where watershed ischaemia bites), cancer staging and genetics, which operation for which segment, and anorectal pathology.

Anatomy

The large bowel is recognised by three features absent from small bowel: taeniae coli, haustra and appendices epiploicae. The rectum has none — the taeniae fan out into a complete longitudinal coat at the rectosigmoid junction.

Segments:

- ➡ Caecum + appendix (RIF, intraperitoneal)

- ➡ Ascending colon (retroperitoneal)

- ➡ Hepatic flexure → transverse colon (intraperitoneal, on transverse mesocolon)

- ➡ Splenic flexure (higher and more acute than hepatic — watershed zone)

- ➡ Descending colon (retroperitoneal)

- ➡ Sigmoid (intraperitoneal, on sigmoid mesocolon — mobile, hence volvulus)

- ➡ Rectum (upper third peritoneal anteriorly and laterally; middle third anteriorly only; lower third extraperitoneal)

- ➡ Anal canal (below dentate line)

The dentate (pectinate) line is the embryological hinge of the anal canal. Above: hindgut endoderm, columnar epithelium, visceral innervation (painless), portal drainage via superior rectal vein, internal iliac nodes. Below: ectoderm, squamous epithelium, somatic innervation (pain-sensitive, via inferior rectal nerve), systemic drainage, superficial inguinal nodes. This split explains internal (painless) vs external (painful) haemorrhoids and why anal cancer below the dentate is squamous and spreads to groin.

──────────────────────────────

Blood supply

Two mesenteric arteries divide at the midgut–hindgut junction (mid-transverse colon).

SMA (L1) supplies midgut to mid-transverse colon:

- ➡ Ileocolic — terminal ileum, caecum, appendix

- ➡ Right colic — ascending colon

- ➡ Middle colic — transverse colon

IMA (L3) supplies hindgut to upper anal canal:

- ➡ Left colic — descending colon

- ➡ Sigmoid branches — sigmoid

- ➡ Superior rectal — upper rectum

Middle and inferior rectal arteries arise from the internal iliac, not the IMA.

The marginal artery of Drummond anastomoses SMA and IMA along the mesenteric border. The anastomosis is weakest at the splenic flexure (Griffiths' point) and rectosigmoid junction (Sudeck's point) — these segments infarct first in low-flow states (ischaemic colitis).

👩‍⚕️ Midgut to mid-transverse = SMA; hindgut downstream = IMA. Name the segment, name the artery.

Rectum and mesorectum

The rectum begins at S3 and is surrounded by the mesorectum — a fatty envelope containing lymphatics and the superior rectal vessels within the mesorectal fascia. Cancer tracks within this envelope, which is why total mesorectal excision (TME) — sharp dissection along the mesorectal fascia — is the oncological gold standard for mid and low rectal cancer.

Colorectal cancer

Adenoma–carcinoma sequence

Most CRC arises through stepwise mutations over 10–15 years:

Normal mucosa → APC loss → small adenoma → KRAS activation → large adenoma → p53 / DCC loss → invasive carcinoma.

Polypectomy interrupts this sequence and prevents cancer.

Hereditary syndromes

Syndrome	Gene	Pattern	Extra-colonic features
FAP	APC (tumour suppressor)	Hundreds–thousands of tubular adenomas; 100% risk of CRC by 40	Prophylactic colectomy mandated
Gardner	APC variant	FAP + osteomas, supernumerary teeth, epidermoid cysts, desmoids
Turcot	APC or MMR	FAP + CNS tumours (medulloblastoma, glioblastoma)
Lynch (HNPCC)	MMR genes (MLH1, MSH2, MSH6, PMS2) — microsatellite instability	Few polyps, right-sided CRC, young age	Endometrial, ovarian, gastric, urothelial cancers
Peutz–Jeghers	STK11	Hamartomatous polyps → intussusception	Perioral mucocutaneous pigmentation; raised cancer risk
Cowden	PTEN	Hamartomatous polyps	Trichilemmomas, breast, thyroid, endometrial cancer

👩‍⚕️ Lynch = few polyps, cancer arises de novo, surveillance needs colonoscopy. FAP = carpets of adenomas.

Presentation

- Right-sided: iron-deficiency anaemia, weight loss, RIF mass (wide lumen, liquid stool — obstructs late).

- Left-sided: change in bowel habit, PR bleeding, obstruction.

- Rectal: fresh PR bleeding, tenesmus, mucus.

👩‍⚕️ Iron-deficiency anaemia in a man or post-menopausal woman is colorectal cancer until proven otherwise.

TNM (8th edition)

- T1 submucosa; T2 muscularis propria; T3 through muscularis into pericolorectal tissue; T4a visceral peritoneum; T4b adjacent organs.

- N0 none; N1a 1 node; N1b 2–3; N2a 4–6; N2b ≥ 7.

- M1a one site; M1b multiple; M1c peritoneal.

Dukes': A (bowel wall) → B (through wall) → C (nodes) → D (distant).

UK screening: FIT every 2 years from 50–74; positive → colonoscopy.

Operations

Resect the diseased segment with its arterial pedicle and lymphatic drainage.

Operation	Segment removed	Artery ligated
Right hemicolectomy	Caecum, ascending, hepatic flexure	Ileocolic + right colic (+ right branch middle colic)
Extended right hemicolectomy	+ transverse	+ middle colic
Left hemicolectomy	Descending colon	Left colic
Sigmoid colectomy	Sigmoid	Sigmoid branches of IMA
(High) anterior resection	Upper rectum + sigmoid	IMA at origin; primary anastomosis
Low anterior resection (LAR)	Mid/low rectum with TME	IMA; coloanal anastomosis ± defunctioning loop ileostomy
Abdominoperineal resection (APR)	Lower rectum + anal canal	IMA; permanent end colostomy
Hartmann's procedure	Sigmoid (emergency)	Resect, oversew rectal stump, end colostomy
Total colectomy	Entire colon	For FAP, UC, fulminant colitis

👩‍⚕️ APR vs LAR depends on whether the sphincter can be preserved with an adequate distal margin (≥ 1–2 cm). Tumours within 1 cm of the anorectal junction = APR with permanent end colostomy. Hartmann's is the emergency option for an unstable patient with perforated diverticulitis or obstructing left-sided cancer.

Stomas

Feature	Colostomy	Ileostomy
Site	Left iliac fossa	Right iliac fossa
Spout	Flush with skin	Spouted (~2.5 cm) — protects skin from enzyme-rich effluent
Effluent	Formed/semi-formed faeces	Liquid, green-brown
Loop vs end	Loop = defunctioning, two openings; end = single opening, distal bowel removed or oversewn	Same

👩‍⚕️ A spouted stoma on the right is an ileostomy; flush on the left is a colostomy. Mix them up and you lose an easy mark.

Inflammatory bowel disease

(Crohn's is covered in Lesson 52.)

	Ulcerative colitis	Crohn's disease
Distribution	Rectum upwards, continuous	Mouth to anus, skip lesions
Depth	Mucosa and submucosa only	Transmural
Histology	Crypt abscesses, goblet-cell depletion	Non-caseating granulomas
Macroscopic	Pseudopolyps, lead-pipe colon	Cobblestoning, strictures, fistulae
Smoking	Protective (counter-intuitive)	Worsens disease
Complications	Toxic megacolon, dysplasia → CRC, PSC	Fistulae, abscesses, strictures, perianal disease
Surgery	Curative — total colectomy + IPAA	Not curative — recurs

UC carries a substantial CRC risk that rises with duration (> 8–10 years) and extent (pancolitis). Surveillance colonoscopy hunts for dysplasia. Medical: 5-ASA maintenance, steroids for flares, biologics (infliximab, vedolizumab) for refractory disease. Surgery (curative): toxic megacolon, perforation, massive bleeding, dysplasia/cancer, failed medical therapy.

Diverticular disease

False diverticula at vasa recta penetration points, most often sigmoid (high luminal pressure).

Complications: diverticulitis (LIF pain, fever), abscess, perforation, colovesical fistula (pneumaturia, recurrent UTI), stricture, painless bleeding.

Hinchey classification: I pericolic abscess; II pelvic abscess; III purulent peritonitis; IV faecal peritonitis. Hinchey I–II → antibiotics ± drainage. Hinchey III–IV → Hartmann's.

Large bowel obstruction

Top three: colorectal cancer (commonest), diverticular stricture, sigmoid volvulus.

A competent ileocaecal valve creates a closed-loop obstruction — caecum perforates first (Laplace). An incompetent valve decompresses into the small bowel, giving combined small and large bowel air–fluid levels — classic for obstructing CRC.

Sigmoid volvulus: elderly, institutionalised, chronic constipation. AXR shows the coffee bean sign (loop from LIF to RUQ). Management: flexible sigmoidoscopic decompression + flatus tube; sigmoid colectomy if ischaemia, peritonitis or recurrence.

Caecal volvulus: younger patients with mobile caecum, dilated loop in LUQ. Treatment: right hemicolectomy.

Anal pathology

Haemorrhoids — engorged anal cushions at 3, 7, 11 o'clock. Internal (above dentate, columnar, painless bleeding, prolapse, graded I–IV); external (below dentate, squamous, painful when thrombosed). Ladder: fibre → banding (II–III) → haemorrhoidectomy (IV / failed).

Anal fissure — linear tear in the posterior midline (watershed of inferior rectal artery). Severe pain during/after defecation, fresh bleeding, sphincter spasm. First-line: topical GTN 0.4% or diltiazem 2% (relax internal sphincter); botulinum toxin second-line; lateral internal sphincterotomy for refractory disease (small incontinence risk). Lateral or atypical fissures suggest Crohn's, TB, HIV or malignancy.

Abscesses — cryptoglandular origin. Perianal (superficial, fluctuant lump) and ischioanal (deep in fossa: medial wall = external sphincter + levator ani; lateral wall = obturator internus + ischial tuberosity). Treatment is always incision and drainage — antibiotics alone fail.

Anal fistula — track between anal canal and perianal skin, usually post-abscess. Goodsall's rule: external openings anterior to a transverse anal line track radially to the dentate line; posterior openings curve to the posterior midline. MRI pelvis maps complex/Crohn's fistulas. Simple low → fistulotomy; complex/Crohn's → loose seton, LIFT, advancement flap, fibrin glue, bioprosthetic plug, FILAC.

👩‍⚕️ Recurrent, multiple, treatment-resistant perianal fistulas in a young patient = Crohn's. Drain, set, treat medically — avoid sphincter-cutting procedures.

Anal cancer: above dentate = adenocarcinoma (treat as rectal). Below = squamous cell carcinoma (HPV-associated, inguinal nodes). Treatment is chemoradiotherapy (Nigro: 5-FU + mitomycin C + RT) — sphincter-preserving and curative in most. APR is reserved for failure or recurrence.

Pseudomembranous colitis

C. difficile overgrowth after broad-spectrum antibiotics — the 4 Cs (clindamycin, cephalosporins, ciprofloxacin, co-amoxiclav). Profuse watery diarrhoea, raised WCC/lactate, yellow pseudomembranes on colonoscopy. Oral vancomycin or fidaxomicin first-line; metronidazole for mild disease; FMT for recurrence; subtotal colectomy for toxic megacolon or perforation.

Ischaemic colitis

Low-flow injury, most often at the splenic flexure. Elderly vasculopath, sudden left-sided pain and bloody diarrhoea; thumbprinting on imaging. Usually resolves with bowel rest, IV fluids and antibiotics; surgery for full-thickness necrosis, perforation or stricture. Distinguish from acute mesenteric ischaemia (SMA occlusion — sudden severe central pain out of proportion to signs, lactic acidosis, needs emergency revascularisation).

[Image: MCQs banner]

Test yourself

Which artery supplies the transverse colon?

((Middle colic::☑️ Branch of SMA; supplies transverse colon up to splenic flexure watershed.))
((Right colic::Ascending colon only.))
((Left colic::Branch of IMA, supplies descending colon.))
((Superior rectal::Terminal IMA, supplies upper rectum.))
((Ileocolic::Terminal ileum, caecum, appendix.))

👩‍⚕️ The mid-transverse colon is the embryological midgut–hindgut junction and Griffiths' watershed point.

An elderly man with brisk PR bleeding has angiographic embolisation planned for sigmoid bleeding. Which artery should be targeted?

((Left colic / sigmoid branches of IMA::☑️ Sigmoid is supplied by sigmoid branches of IMA.))
((Middle colic::Transverse colon, not sigmoid.))
((Right colic::Ascending colon.))
((Superior rectal::Upper rectum, distal to sigmoid.))
((Inferior rectal::Lower anal canal, from internal pudendal.))

A patient is prepared for high anterior resection. Which artery is ligated, and at what vertebral level does it arise?

((Inferior mesenteric artery — L3::☑️ IMA supplies the hindgut from mid-transverse to upper rectum.))
((SMA — L1::Supplies midgut, not the rectum.))
((Coeliac trunk — T12::Supplies foregut.))
((Median sacral — L4/L5::Tiny midline branch; not relevant.))
((Internal iliac — pelvis::Gives middle and inferior rectal but not the resection pedicle.))

A 55-year-old presents with absolute constipation and AXR showing air–fluid levels in both small and large bowel. Most likely diagnosis?

((Obstructing colorectal carcinoma::☑️ Most common cause of large bowel obstruction over 50; combined levels imply incompetent ileocaecal valve.))
((Sigmoid volvulus::Would show coffee bean sign, not combined small/large levels.))
((Diverticular stricture::Possible but less common than malignancy in this age group.))
((Adhesions::Cause small bowel obstruction, not large.))
((Pseudo-obstruction::No mechanical cause; usually post-op or unwell inpatient.))

A man with right iliac fossa pain has a smooth, regular, well-defined mass that does not move with respiration. Most likely diagnosis?

((Caecal tumour::☑️ Right-sided cancer presents late with mass and iron-deficiency anaemia.))
((Appendix mass::Tender, recent history of appendicitis-like illness.))
((Meckel's diverticulum::Usually presents in childhood with bleeding or intussusception.))
((Visceroptotic kidney::Ballotable, moves with respiration.))
((Gallbladder mucocele::RUQ, moves with respiration.))

Pathology of a resected caecal cancer reports it as T4. What does this mean?

((Tumour penetrates visceral peritoneum or directly invades adjacent organs::☑️ T4a = visceral peritoneum; T4b = adjacent structures.))
((Submucosal invasion::T1.))
((Invasion of muscularis propria::T2.))
((Through muscularis into pericolorectal tissue::T3.))
((Lymphovascular invasion::Histological feature, not a T stage.))

Low anterior resection for rectal cancer: tumour invades abdominal wall, 2/24 nodes positive, no distant metastasis. TNM stage?

((T4N1M0::☑️ T4 = adjacent structures; N1b = 2–3 nodes; M0 = no mets.))
((T3N1M0::T3 is through muscularis but not into abdominal wall.))
((T4N2M0::N2 requires ≥ 4 positive nodes.))
((T4N1M1::M1 would require distant metastasis.))
((T3N2M0::Wrong T and wrong N.))

Elderly hypertensive man with two days of bloody diarrhoea and left-sided abdominal tenderness; AXR shows thumbprinting. Diagnosis?

((Ischaemic colitis::☑️ Watershed (splenic flexure) injury; thumbprinting reflects submucosal oedema.))
((Ulcerative colitis::Younger patient, longer history, lead-pipe colon.))
((Pseudomembranous colitis::Recent antibiotic exposure; profuse watery diarrhoea.))
((Diverticulitis::Pain and fever dominate; bleeding is painless when it occurs.))
((Mesenteric ischaemia (SMA)::Central abdominal pain out of proportion to signs, severe acidosis.))

A 45-year-old presents with sudden massive PR bleeding, no prior episodes, HR 110, BP 90/60. Most likely cause?

((Angiodysplasia::☑️ Painless massive lower GI bleed in adults > 40; often right colon, easily missed on colonoscopy.))
((Diverticular bleed::Possible but typically older; painless.))
((Haemorrhoids::Rarely cause haemodynamic instability.))
((Colorectal cancer::Bleeding is usually occult or modest.))
((Ischaemic colitis::Associated with pain, not painless massive bleed.))

A 50-year-old with 30-year pancolitis has a plaque-like lesion on surveillance colonoscopy. The premalignant change is called what?

((Dysplasia::☑️ Premalignant epithelial change; long-standing UC carries high CRC risk after 8–10 years.))
((Metaplasia::Replacement of one epithelium with another; not premalignant per se.))
((Hyperplasia::Increased cell number, not premalignant.))
((Anaplasia::Loss of differentiation seen in established malignancy.))
((Atrophy::Reduction in tissue mass; not premalignant.))

Routine colonoscopy fails to pass the hepatic flexure. Next best investigation?

((CT colonography::☑️ Non-invasive virtual colonoscopy; visualises proximal colon when scope cannot reach.))
((Repeat colonoscopy without preparation::Will fail for the same reason.))
((PET scan::Functional, not diagnostic for mucosal lesions.))
((Abdominal ultrasound::Poor for colonic mucosa.))
((MRI abdomen::Slow and not first-line for colonic luminal assessment.))

Post-polypectomy in the right colon, small free air under the diaphragm, patient well. Most appropriate management?

((Conservative with IV antibiotics, NBM and close observation::☑️ Small contained perforation with good prep and no sepsis can be managed non-operatively.))
((Immediate laparotomy::Reserved for deterioration, large perforation or sepsis.))
((Diagnostic laparoscopy::Only if conservative management fails.))
((Endoscopic clipping now::Done at time of perforation, not after CT.))
((Discharge home::Free intraperitoneal air mandates admission.))

A 23-year-old with mucocutaneous pigmentation and previous intussusception. Likely colonic lesion?

((Hamartomatous polyps::☑️ Peutz–Jeghers — STK11 mutation; perioral pigmentation, intussusception, raised cancer risk.))
((Tubular adenoma::FAP — hundreds of adenomas, not hamartomas.))
((Hyperplastic polyps::Common incidental finding, not associated with this syndrome.))
((Inflammatory pseudopolyps::Seen in UC, not in this clinical picture.))
((Juvenile polyps::Juvenile polyposis syndrome; no mucocutaneous pigmentation.))

A family history of endometrial, ovarian and colorectal cancer in young relatives. Most likely diagnosis?

((Lynch syndrome (HNPCC)::☑️ Mismatch repair gene mutation (MLH1, MSH2, MSH6, PMS2); few polyps, right-sided CRC, endometrial/ovarian risk.))
((FAP::Hundreds of adenomas; CRC not extra-colonic cluster.))
((Peutz–Jeghers::Hamartomas with mucocutaneous pigmentation.))
((Cowden::Breast, thyroid and endometrial; trichilemmomas.))
((BRCA::Breast and ovarian; no CRC association.))

Typical colonic polyp in FAP?

((Tubular adenoma::☑️ APC mutation produces hundreds–thousands of adenomatous polyps; 100% CRC risk by 40.))
((Hamartoma::Peutz–Jeghers or juvenile polyposis.))
((Hyperplastic polyp::Not adenomatous, low malignant potential.))
((Inflammatory pseudopolyp::UC.))
((Serrated adenoma::A separate molecular pathway, not the FAP picture.))

A 74-year-old with sigmoid perforation and faecal peritonitis, BP 90/60. Operation?

((Hartmann's procedure::☑️ Resect sigmoid, end colostomy, oversew rectal stump — fastest source control in an unstable patient.))
((Primary anastomosis::High leak risk in faecal peritonitis.))
((Laparoscopic lavage::Limited evidence; not for Hinchey IV.))
((Defunctioning loop colostomy alone::Leaves perforated bowel in situ.))
((Conservative antibiotics::Faecal peritonitis is a surgical emergency.))

Seven days after sigmoid resection, fever and abdominal pain. Most likely cause?

((Intra-abdominal sepsis / anastomotic leak::☑️ Classic timing for leak or collection (day 5–7).))
((Atelectasis::Earlier (day 1–2), respiratory signs.))
((UTI::Possible but unlikely to dominate the picture.))
((Pulmonary embolism::Pleuritic chest pain, tachycardia, hypoxia.))
((Wound infection::Superficial cellulitis, less systemic upset.))

Ten days after colostomy reversal, vomiting, colicky pain and tender swelling at the previous stoma site. Diagnosis?

((Obstructed incisional hernia at stoma site::☑️ Stoma-site closures have a notoriously high incisional hernia rate.))
((Anastomotic leak::Earlier, peritonitic.))
((Adhesional obstruction::Possible but no swelling at the site.))
((Haematoma::Painful but not obstructive.))
((Anastomotic stricture::Gradual onset, no swelling.))

Why does appendicitis pain start centrally before localising to the RIF?

((Visceral afferents from the appendix enter the cord at T10, referring pain to the periumbilical (T10) dermatome::☑️ As inflammation reaches parietal peritoneum, somatic fibres localise pain to McBurney's point.))
((Pain is carried initially by the vagus nerve::Vagus has no visceral pain fibres for the midgut.))
((The appendix first irritates the subcostal nerve::Anatomically wrong.))
((Both anterior and posterior peritoneum are inflamed simultaneously::Not the mechanism of referred pain.))
((Phrenic referral pattern::Phrenic refers to shoulder, not periumbilicus.))

In acute appendicitis, the predominant inflammatory cell on histology is?

((Neutrophils::☑️ Hallmark of acute suppurative inflammation, infiltrating muscularis propria.))
((Lymphocytes::Chronic inflammation.))
((Eosinophils::Parasitic or allergic.))
((Plasma cells::Chronic.))
((Macrophages::Granulomatous inflammation.))

A pus collection after appendicectomy — likely site?

((Rectouterine pouch of Douglas::☑️ Most dependent peritoneal recess in females; common site for post-appendicectomy abscess.))
((Subphrenic space::Possible but less common.))
((Right paracolic gutter::A track, not a typical collection site.))
((Lesser sac::Accessed through foramen of Winslow; unusual after appendicectomy.))
((Hepatorenal recess (Morison's)::Common in supine patients but not as common as pelvis.))

A man with two days of perianal pain and a soft fluctuant tender mass on DRE. Most appropriate management?

((Incision and drainage::☑️ Perianal abscess — antibiotics alone will not suffice.))
((Antibiotics only::Inadequate; abscesses need drainage.))
((Haemorrhoidectomy::Wrong pathology.))
((Excision biopsy::Not for an abscess.))
((MRI then conservative::Delays drainage.))

Medial wall of the ischioanal fossa is formed by?

((External anal sphincter and levator ani::☑️ Medial wall of ischioanal fossa; lateral wall is obturator internus and ischial tuberosity.))
((Obturator internus::Lateral wall.))
((Ischial tuberosity::Lateral wall.))
((Pudendal canal::Sits in the lateral wall (Alcock's canal).))
((Sacrotuberous ligament::Posterior boundary.))

A 24-year-old with recurrent perianal fistulas not responding to treatment. Likely diagnosis?

((Crohn's disease::☑️ Transmural inflammation predisposes to fistulae; recurrent, multiple, treatment-resistant fistulae in young patients are classic.))
((Ulcerative colitis::Mucosal disease; fistulae are not characteristic.))
((Idiopathic cryptoglandular::Usually solitary, not recurrent on optimal treatment.))
((TB::Rare in UK practice.))
((Hidradenitis suppurativa::Affects apocrine skin (axilla, groin), not anal canal.))

A 30-year-old with Crohn's develops a perianal fistula. Most appropriate next step?

((MRI pelvis::☑️ Gold standard imaging to map tract, sphincter involvement and occult abscesses before any intervention.))
((Fistulotomy::Risks incontinence in complex Crohn's fistulae.))
((Lay open::Same — avoided in Crohn's.))
((Loose seton without imaging::Reasonable adjunct after imaging defines anatomy.))
((Examination under anaesthesia only::Imaging precedes EUA for complex fistulae.))

A man on long-term opioids with constipation and painful fresh bleeding after defecation. Diagnosis?

((Anal fissure::☑️ Hard stool tears the posterior midline; severe pain during/after defecation, fresh blood on the paper.))
((Internal haemorrhoids::Painless bleeding.))
((Thrombosed external haemorrhoid::Painful lump, not associated with bleeding after defecation.))
((Rectal cancer::Possible but pain is not characteristic.))
((Proctitis::Mucus, tenesmus, urgency dominate.))

Initial management of a posterior anal fissure in a 23-year-old?

((Topical GTN 0.4% (or diltiazem 2%)::☑️ Relaxes internal sphincter, restores blood flow, heals most acute fissures.))
((Lateral internal sphincterotomy::Surgical, reserved for chronic/refractory fissures.))
((Botulinum toxin injection::Second-line if topical therapy fails.))
((Lord's procedure::Historic; risk of incontinence — abandoned.))
((Endoanal advancement flap::Reserved for complex recurrent fissures.))

A 55-year-old with biopsy-confirmed anal squamous cell carcinoma, no metastatic disease. Treatment of choice?

((Radical chemoradiotherapy (Nigro regimen)::☑️ 5-FU + mitomycin C + radiotherapy; sphincter-preserving and curative in most.))
((Abdominoperineal resection::Reserved for persistent or recurrent disease after chemoradiation.))
((Radiotherapy alone::Inferior to combined chemoradiation.))
((Chemotherapy alone::Inferior to combined chemoradiation.))
((Local excision::Inadequate for invasive disease.))

A 29-year-old porter has a prolapsed perianal swelling and haematoma after heavy lifting. Diagnosis?

((Rectal prolapse / prolapsed thrombosed haemorrhoid::☑️ Sudden increased intra-abdominal pressure precipitates prolapse, particularly with chronic constipation.))
((Anal fissure::Linear tear, not a prolapsed mass.))
((Perianal abscess::Tender fluctuant, no prolapsed swelling.))
((Anal fistula::Discharging opening, not a prolapsed mass.))
((Anal cancer::Mass would be hard, not a sudden prolapse.))

Revision summary

- SMA (L1) = midgut → mid-transverse (ileocolic, right colic, middle colic). IMA (L3) = hindgut downstream (left colic, sigmoid, superior rectal). Middle/inferior rectal = internal iliac.

- Marginal artery of Drummond weakest at splenic flexure (Griffiths') — ischaemic colitis.

- Rectum: no taeniae/haustra/appendices. Mesorectum → TME for mid/low rectal cancer.

- Dentate line: above = hindgut, painless, portal, internal iliac nodes; below = ectoderm, painful, systemic, inguinal nodes.

- Adenoma–carcinoma: APC → KRAS → p53. FAP (APC, carpets, 100% CRC); Lynch (MMR, few polyps, right-sided, endometrial/ovarian).

- Right cancer = anaemia/mass. Left = obstruction/bleeding.

- Operations: right hemi (to hepatic flexure); extended right (+ transverse); left hemi (descending); sigmoid colectomy; anterior resection (upper rectum); LAR + TME (mid); APR (lower, permanent end colostomy); Hartmann's (emergency sigmoid).

- Stomas: colostomy LIF, flush; ileostomy RIF, spouted.

- UC: continuous, rectum upwards, mucosa/submucosa, crypt abscesses, toxic megacolon, ↑ CRC; colectomy curative.

- Diverticular: sigmoid; Hinchey III/IV → Hartmann's.

- Sigmoid volvulus: coffee bean → flexible sigmoidoscopic decompression. Caecal volvulus: right hemi.

- Haemorrhoids: internal painless, external painful. Fissure: posterior midline, GTN/diltiazem first. Abscess: I&D. Fistula: MRI pelvis, Goodsall's.

- Anal SCC: Nigro chemoradiotherapy.

- C. diff: 4 Cs → oral vancomycin or fidaxomicin.

- Ischaemic colitis: elderly vasculopath, splenic flexure, thumbprinting.