Surgery: Colorectal and anal surgery

🩺 Colorectal and anal surgery -page 5 of the Surgery chapter. Colorectal cancer is the fourth commonest cancer in the UK and is curable when caught early -so change in bowel habit, rectal bleeding, iron deficiency anaemia and a positive FIT need prompt investigation. Most anal symptoms are benign (haemorrhoids, fissures, abscesses), but always examine the patient -anal and rectal cancers can look like piles. Medical IBD and bowel disorders are in the Gastroenterology chapters; colonic emergencies (obstruction, volvulus) are also on the Acute Abdomen page.
Your four questions for every patient: Could this be cancer -and does the patient meet urgent referral criteria? Is there an emergency (obstruction, perforation, bleeding, sepsis)? What does examination (including rectal examination) show? What treatment is right for this patient's fitness and wishes -and will they need a stoma?

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Lower GI Symptoms and Referral

• FIT (faecal immunochemical test) -measures tiny amounts of blood in stool; now central to deciding who needs urgent investigation.
• Refer urgently (suspected cancer pathway) (NICE NG12 and DG56):
  • Adults with symptoms suggesting colorectal cancer and a FIT of 10 micrograms of haemoglobin per gram or more.
  • A rectal or abdominal mass, or an unexplained anal mass or ulcer -refer even if FIT is negative.
• Symptoms that should prompt FIT and assessment -change in bowel habit, rectal bleeding, iron deficiency anaemia, unexplained abdominal pain, weight loss, a mass.
• Investigations -colonoscopy (the gold standard -can biopsy and remove polyps), CT colonography (if colonoscopy unsuitable or incomplete), flexible sigmoidoscopy (for isolated rectal bleeding in some), CT staging if cancer is found.
• Always examine -abdomen and digital rectal examination (a third of rectal cancers can be felt).
• Iron deficiency anaemia in men and postmenopausal women -gastroscopy and colonoscopy (or CT colonography), plus coeliac serology (see the Haematology chapters).

Bowel Cancer Screening and Polyps

• NHS Bowel Cancer Screening Programme (England) -a home FIT kit every 2 years from age 50 to 74; a positive result leads to colonoscopy. Screening detects cancers earlier and removes polyps before they become cancer.
• Polyps:
  • Adenomas (tubular, tubulovillous, villous) -precancerous; risk of cancer rises with size (especially 1 cm or more), villous features and high-grade dysplasia.
  • Serrated polyps (sessile serrated lesions) -precancerous, often in the right colon, harder to see.
  • Hyperplastic polyps (small, in the rectum and sigmoid) -usually harmless.
  • Inflammatory (pseudo)polyps in IBD; hamartomas in Peutz–Jeghers and juvenile polyposis.
• Most polyps are removed at colonoscopy (polypectomy, endoscopic mucosal resection); large or difficult ones may need advanced endoscopy or surgery; risks -bleeding and perforation.
• Surveillance after polyps (BSG guidance) -colonoscopy at 3 years for higher-risk findings (e.g. 2 or more premalignant polyps including an advanced one, or 5 or more premalignant polyps, or a large polyp removed in pieces); otherwise return to routine screening.
• Malignant polyps (cancer within a removed polyp) -MDT decision whether polypectomy is enough or bowel resection is needed.

Inherited Bowel Cancer Syndromes

Syndrome	Gene	Key features and management
Lynch syndrome (hereditary non-polyposis colorectal cancer)	Mismatch repair genes (MLH1, MSH2, MSH6, PMS2) -autosomal dominant	The commonest inherited cause; colorectal cancer at a young age (often right-sided), endometrial, ovarian, stomach, urinary tract and other cancers; all colorectal and endometrial cancers are tested for mismatch repair deficiency; colonoscopy every 2 years from about 25; aspirin to reduce risk; gynaecological risk-reducing surgery
Familial adenomatous polyposis (FAP)	APC -autosomal dominant	Hundreds to thousands of adenomas from the teens; near-certain cancer without surgery -prophylactic colectomy (usually late teens or early 20s); duodenal adenomas (endoscopic surveillance), desmoid tumours, osteomas, retinal pigment changes
MUTYH-associated polyposis	MUTYH -autosomal recessive	Tens to hundreds of polyps; surveillance or colectomy
Peutz–Jeghers syndrome	STK11	Hamartomatous polyps (small bowel -intussusception), dark freckles on lips and mouth; cancers of GI tract, breast, pancreas, ovary, testis
Juvenile polyposis	SMAD4, BMPR1A	Hamartomatous polyps; bleeding, increased cancer risk; SMAD4 linked with HHT

• Family history -refer to clinical genetics or for surveillance if there are several affected relatives, young-onset cancers, or a known syndrome (BSG/ACPGBI guidance).
• IBD -long-standing extensive colitis (UC or Crohn's colitis) and PSC increase colorectal cancer risk -surveillance colonoscopy (see the IBD chapter).

Colorectal Cancer

• Risk factors -age (most over 60, but rising in younger adults), family history and inherited syndromes, IBD, red and processed meat, low fibre, obesity, inactivity, smoking, alcohol, type 2 diabetes, previous polyps or colorectal cancer, acromegaly.
• Most arise from adenomas over years (the adenoma–carcinoma sequence) -the basis of screening.
• Presentation by site:
  • Right colon (caecum, ascending) -iron deficiency anaemia, weight loss, a mass in the right iliac fossa; bowel habit often normal; may obstruct the ileocaecal valve.
  • Left colon and sigmoid -change in bowel habit, rectal bleeding (dark blood mixed with stool), colicky pain, obstruction.
  • Rectum -bleeding, tenesmus (feeling of incomplete emptying), mucus, change in habit, a mass on rectal examination.
  • Emergency presentations (about 1 in 5) -obstruction, perforation, bleeding -worse outcomes.
• Spread -local, lymph nodes, blood (portal vein → liver first; rectal cancers also to the lungs), peritoneum.
• Staging:
  • CT chest, abdomen and pelvis for all.
  • MRI pelvis for rectal cancer -depth, nodes, and the circumferential resection margin (guides radiotherapy before surgery).
  • CEA (baseline for follow-up -not a screening test), colonoscopy of the whole colon (synchronous tumours), PET-CT in selected cases.
  • TNM staging after surgery decides further treatment.
• MDT -every patient is discussed by the colorectal multidisciplinary team.
• Molecular testing -mismatch repair status (Lynch screening and immunotherapy), RAS and BRAF (targeted therapy choices).

Treating Colorectal Cancer

Tumour site	Usual operation
Caecum, ascending colon, hepatic flexure	Right hemicolectomy (extended for transverse colon)
Splenic flexure, descending colon	Left hemicolectomy (or extended right hemicolectomy)
Sigmoid colon	Sigmoid colectomy or high anterior resection
Upper and mid rectum	Anterior resection with total mesorectal excision (TME); low joins often protected by a temporary loop ileostomy
Low rectum involving the sphincters	Abdominoperineal resection -removes rectum and anus -permanent colostomy
Emergency (obstruction or perforation, left side)	Hartmann's procedure (resection with an end colostomy and the rectal stump closed -possible reversal later), or resection with anastomosis ± defunctioning stoma, or a stent as a bridge

• Approach -laparoscopic or robotic surgery where possible, within an enhanced recovery programme.
• Rectal cancer:
  • Radiotherapy (short course) or chemoradiotherapy (long course) before surgery for higher-risk tumours (threatened margins, nodes); "total neoadjuvant therapy" in some.
  • "Watch and wait" for patients with a complete clinical response after chemoradiotherapy (avoiding surgery with close surveillance).
  • Local excision (transanal) for very early cancers.
• Colon cancer -adjuvant chemotherapy (e.g. capecitabine and oxaliplatin) after surgery for stage III (node-positive) and some high-risk stage II cancers.
• Metastatic disease -liver and lung metastases may be resected or ablated for cure in selected patients; chemotherapy, targeted drugs (anti-EGFR for RAS wild-type, anti-VEGF) and immunotherapy (for mismatch repair-deficient cancers); stents and palliative care.
• Complications of surgery -anastomotic leak (days 5–7), ileus, bleeding, wound infection, VTE, injury to ureters, bladder and pelvic nerves (urinary and sexual dysfunction after rectal surgery).
• Low anterior resection syndrome -urgency, frequency, clustering of stools and incontinence after rectal surgery -common; improves over time; diet, loperamide, pelvic floor therapy, irrigation.
• Follow-up -CEA and CT for several years, colonoscopy at 1 year after surgery then per guidance.

Diverticular Disease

• Diverticulosis -pouches of mucosa pushing through weak points in the bowel wall, usually in the sigmoid colon; very common with age and low-fibre diets; usually no symptoms.
• Diverticular disease -symptoms (lower abdominal pain, bloating, change in bowel habit) without inflammation -high-fibre diet, fluids, analgesia (avoid NSAIDs and opioids where possible).
• Acute diverticulitis -inflamed diverticulum:
  • Left iliac fossa pain and tenderness, fever, change in bowel habit, raised WCC and CRP (in people of Asian descent, right-sided diverticulitis is more common).
  • CT (within 24 hours of admission if complications are suspected) confirms and shows abscesses or perforation.
• Uncomplicated diverticulitis (NICE NG147):
  • Systemically well -analgesia (paracetamol), clear fluids, antibiotics may not be needed ("watchful waiting") -review if not settling within 48 hours.
  • Systemically unwell, immunosuppressed or significant comorbidity -oral antibiotics (e.g. co-amoxiclav for 5 days).
• Complicated diverticulitis (Hinchey classification):
  • Pericolic or pelvic abscess (Hinchey I–II) -IV antibiotics ± CT-guided percutaneous drainage.
  • Purulent peritonitis (Hinchey III) -resection (often with stoma) or laparoscopic lavage in selected patients.
  • Faecal peritonitis (Hinchey IV) -emergency Hartmann's procedure.
• Other complications:
  • Fistula -colovesical (pneumaturia -air in urine, faeces in urine, recurrent UTIs -more common in men or women after hysterectomy), colovaginal (faecal vaginal discharge); elective resection.
  • Stricture (narrowing -obstruction; must exclude cancer).
  • Diverticular bleeding -sudden, painless, large-volume fresh rectal bleeding (see Lower GI Bleeding).
• After an episode -colonoscopy or CT colonography (often about 6 weeks later) to exclude cancer if not already excluded, especially after complicated diverticulitis; high-fibre diet; consider elective resection after complicated or frequent attacks (individual decision).

Surgery for IBD

• Ulcerative colitis (surgery can cure the colitis):
  • Emergency -acute severe UC not responding to IV steroids and rescue therapy (ciclosporin or infliximab) by about day 5–7 (earlier if worsening), toxic megacolon, perforation, severe bleeding -subtotal colectomy with end ileostomy (rectal stump left).
  • Elective -chronic disease not controlled by medicines, steroid dependence, dysplasia or cancer, growth failure in children.
  • Later options -restorative proctocolectomy with ileal pouch–anal anastomosis ("J-pouch" -4–8 bowel movements a day; pouchitis -treated with antibiotics such as metronidazole or ciprofloxacin), or a permanent ileostomy, or ileorectal anastomosis in selected patients.
• Crohn's disease (surgery is not curative -disease often recurs at the join):
  • Indications -strictures causing obstruction (resection or strictureplasty), abscesses (drainage), fistulas, perforation, bleeding, failure of medical treatment, cancer.
  • Preserve bowel -limited resections to avoid short bowel syndrome.
  • Perianal Crohn's -MRI pelvis, examination under anaesthesia, drainage of abscesses, loose setons for fistulas, plus biologics (e.g. infliximab).
  • Stopping smoking reduces recurrence; post-operative medical therapy and colonoscopy at about 6 months.
• Peri-operative care -steroid cover (long-term steroids), nutrition (malnutrition is common), VTE prophylaxis (IBD increases clot risk), timing around biologics.

Stomas

Stoma	Usual site and appearance	Output and uses
Colostomy	Usually left iliac fossa; flush with the skin	Formed stool; after abdominoperineal resection (permanent end colostomy), Hartmann's (end colostomy), or loop colostomy to divert
Ileostomy	Usually right iliac fossa; spouted (protects skin from enzymes)	Liquid output; after colectomy (end ileostomy), or loop ileostomy to protect a low anastomosis (reversed after a few months)
Urostomy (ileal conduit)	Usually right iliac fossa; spouted	Urine; after cystectomy
Feeding or decompression stomas	Gastrostomy (PEG), jejunostomy	Enteral feeding or venting

• Before surgery -stoma nurse marks the best site (away from skin folds, scars and the belt line, visible to the patient), counselling and support.
• Early complications -ischaemia or necrosis (dusky or black stoma), retraction, bleeding, high output, skin irritation, obstruction.
• Later complications -parastomal hernia (very common), prolapse, stenosis, retraction, skin problems, psychological and body image issues.
• High-output ileostomy (over about 1.5–2 L a day) -dehydration, AKI, low sodium and magnesium:
  • Restrict hypotonic drinks (water, tea, juice) and use an oral rehydration solution (e.g. St Mark's solution).
  • Loperamide (often high doses, taken 30–60 minutes before meals) ± codeine, PPI (reduces secretions), octreotide in some.
  • Replace magnesium and sodium; IV fluids if dehydrated; dietitian review; look for causes (infection -C. difficile, obstruction, stopping steroids or opiates).
• Medicines with stomas -modified-release and enteric-coated tablets may pass through an ileostomy unabsorbed (use other forms); avoid unnecessary laxatives with ileostomies; laxatives may be needed with colostomies (constipation); diuretics and ACE inhibitors increase dehydration and AKI risk.

Lower GI Bleeding

• Causes -diverticular bleeding (painless, sudden, large volume), angiodysplasia (older people, aortic stenosis, CKD), haemorrhoids and fissures (bright red on paper), colitis (ischaemic, inflammatory, infective -with diarrhoea), cancer and polyps, post-polypectomy bleeding, radiation proctitis, Meckel's diverticulum (young people).
• Brisk bleeding with shock and a raised urea may be from an upper GI source -consider OGD first.
• Assessment -resuscitate; FBC, clotting, U&E, group and crossmatch; review anticoagulants and antiplatelets; examination including rectal examination.
• Risk -the Oakland score (BSG) -a score of 8 or less identifies minor bleeds safe for outpatient investigation.
• Major or unstable bleeding -CT angiography to locate active bleeding → interventional radiology embolisation; colonoscopy (after bowel preparation) for diagnosis and endoscopic therapy; surgery is a last resort when the site is known.
• Transfusion -restrictive thresholds (Hb under 70 g/L; under 80 g/L with cardiovascular disease); manage anticoagulants (reversal for life-threatening bleeding).

Anal Anatomy and Examination

• Dentate line -above it, the lining has visceral nerves (painless -internal haemorrhoids, rectal cancer); below it, somatic nerves (painful -fissures, thrombosed external piles, abscesses, anal cancer) -see the Gastroenterology Anatomy, Physiology and Pharmacology chapter.
• Sphincters -internal sphincter (involuntary smooth muscle -resting tone; spasm in fissures) and external sphincter (voluntary -squeeze); damage causes incontinence.
• Anal glands open at the dentate line -infection causes most perianal abscesses and fistulas.
• Examination (with consent and a chaperone) -left lateral position, knees drawn up:
  • Inspect -skin tags, prolapsed piles, fissures, external openings of fistulas, abscesses, ulcers, warts, prolapse on straining.
  • Digital rectal examination -tone and squeeze, masses, tenderness, prostate or cervix, blood or mucus on the glove. Avoid DRE with a very painful acute fissure (examine by gentle parting of the buttocks).
  • Proctoscopy (internal haemorrhoids) and rigid or flexible sigmoidoscopy.
• Describe positions using a clock face (in the lithotomy position -12 o'clock is anterior, 6 o'clock posterior).
• Red flags with anal symptoms -change in bowel habit, dark blood mixed with stool, weight loss, anaemia, a mass or ulcer, age over 50 -investigate the colon even if piles are found.

Haemorrhoids

• Haemorrhoids (piles) -swollen vascular cushions in the anal canal; linked with constipation and straining, pregnancy, low-fibre diet, ageing, heavy lifting.
• Internal haemorrhoids (above the dentate line) -painless bright red bleeding (on the paper or dripping into the pan, not mixed with stool), prolapse, mucus discharge, itch. Grades:
  • I -bleed but don't prolapse.
  • II -prolapse on straining and go back by themselves.
  • III -prolapse and need to be pushed back.
  • IV -permanently prolapsed.
• External haemorrhoids (below the dentate line) -covered by skin; usually symptomless unless thrombosed.
• Thrombosed external haemorrhoid -sudden, very painful purple lump at the anal margin; if seen within about 72 hours, excision under local anaesthetic gives fast relief; after that -analgesia, ice, stool softeners (settles over 1–2 weeks).
• Management:
  • All grades -high-fibre diet, fluids, avoid straining and prolonged toilet sitting, stool softeners; short-term topical preparations for symptoms (avoid long-term steroid creams).
  • Grades I–III -rubber band ligation in clinic (pain, bleeding, rarely sepsis -warn about severe pain, fever or urinary retention), injection sclerotherapy, haemorrhoidal artery ligation.
  • Grades III–IV or failed banding -haemorrhoidectomy (painful recovery; bleeding, urinary retention, anal stenosis, incontinence rarely) or stapled haemorrhoidopexy.
• Strangulated (thrombosed prolapsed internal) haemorrhoids -very painful, swollen, dark prolapsed piles -analgesia, ice, softeners, sometimes emergency surgery.

Anal Fissure

• A tear in the anal lining below the dentate line -usually after passing a hard stool; the pain causes internal sphincter spasm, which reduces blood flow and stops healing (a vicious circle).
• Features -severe pain on and after passing stool ("like passing glass"), lasting minutes to hours; bright red blood on the paper; fear of opening bowels → more constipation.
• Site -posterior midline in about 90% (anterior midline is more common in women after childbirth). Off-midline or multiple fissures suggest another cause -Crohn's disease, TB, HIV, syphilis, herpes, or anal cancer -investigate.
• Acute (under 6 weeks) versus chronic (over 6 weeks -raised edges, a sentinel pile or skin tag, exposed sphincter fibres).
• Management:
  • Soften stools (fibre, fluids, laxatives such as macrogol or ispaghula), sitz baths, simple analgesia, topical lidocaine before bowel movements.
  • Topical GTN 0.4% ointment (relaxes the sphincter -headache is common) or topical diltiazem 2% (fewer headaches) twice daily for 6–8 weeks -for chronic fissures, or acute fissures not settling.
  • Refer if not healed after about 8 weeks of treatment -botulinum toxin injection, or lateral internal sphincterotomy (most effective, small risk of incontinence -avoided in women at risk).

Perianal Abscess and Fistula

• Perianal abscess -infection of an anal gland:
  • Throbbing perianal pain (worse sitting), a red, hot, tender swelling, fever; deeper (ischiorectal, intersphincteric, supralevator) abscesses may show little on the surface but cause severe pain and sepsis.
  • Treatment -incision and drainage (usually under anaesthetic) -antibiotics alone don't work; antibiotics added for cellulitis, diabetes, immunosuppression or sepsis.
  • Check for diabetes; consider Crohn's disease with recurrent or complex abscesses; Fournier's gangrene if spreading necrosis (emergency).
• Fistula-in-ano -an abnormal tract between the anal canal and the perianal skin; develops in up to about half of patients after an abscess:
  • Persistent discharge of pus or blood, recurrent abscesses, an external opening near the anus.
  • Goodsall's rule -an external opening in front of the transverse anal line usually tracks straight to the canal; one behind it usually curves to the posterior midline.
  • MRI pelvis (or endoanal ultrasound) maps complex fistulas.
  • Treatment -depends on how much sphincter the tract crosses: fistulotomy (laying open) for low, simple fistulas; setons (loose -to drain; cutting -slowly), advancement flaps or LIFT procedures for high fistulas to protect continence.
  • Causes other than gland infection -Crohn's disease, TB, HIV, cancer, radiation, trauma.

Pilonidal Disease and Pruritus Ani

• Pilonidal sinus -hair driven into the skin of the natal cleft (between the buttocks), causing sinuses, cysts and abscesses:
  • Typically young, hairy men; sitting for long periods; obesity.
  • Small midline pits, painful swelling, recurrent discharge.
  • Abscess -incision and drainage (off the midline); chronic disease -excision with laying open, primary closure or flap techniques (off-midline closure has fewer recurrences); hair removal and hygiene help prevent recurrence.
• Pruritus ani (itchy bottom):
  • Causes -poor hygiene or over-cleaning (soaps, wet wipes), leakage of stool or mucus (piles, fissures, incontinence), diet (caffeine, spicy food), skin diseases (eczema, psoriasis, lichen sclerosus, contact dermatitis), infections (threadworm -especially children, candida, tinea, warts), diabetes, anal cancer and precancer (rare).
  • Management -treat the cause; gentle cleaning with water, pat dry, barrier cream, avoid scratching and irritants; short-term mild steroid cream; examine and biopsy if persistent or abnormal skin.

Rectal Prolapse

• Full-thickness rectal prolapse -the whole rectal wall protrudes through the anus, with concentric rings of mucosa; mostly older women (also linked to chronic constipation, straining, pelvic floor weakness, previous childbirth, psychiatric and neurological conditions).
• Mucosal prolapse -only the lining (radial folds) -often with haemorrhoids.
• Children -usually mucosal; consider cystic fibrosis, constipation, diarrhoea, malnutrition.
• Symptoms -a lump on straining, mucus, bleeding, faecal incontinence or constipation; an irreducible or ischaemic prolapse is an emergency.
• Management -treat constipation; reduce gently (sugar on oedematous prolapse helps reduce swelling); surgery:
  • Abdominal approach (laparoscopic ventral mesh rectopexy) -fitter patients, lower recurrence.
  • Perineal approach (Delorme's or Altemeier's procedure) -frail patients, higher recurrence.
• Internal rectal intussusception and rectocele can cause obstructed defecation (see below).

Anal Cancer

• Usually squamous cell carcinoma, linked to HPV (types 16 and 18); risk factors -HIV, men who have sex with men, receptive anal sex, smoking, immunosuppression (transplant), previous cervical, vulval or vaginal HPV disease.
• Features -anal bleeding, pain, a lump or ulcer, itch, discharge, change in bowel habit, inguinal lymph nodes (below the dentate line drains to the groin) -often mistaken for piles or fissures.
• Precancer -anal intraepithelial neoplasia (AIN); screening for high-risk groups in some services.
• Diagnosis -examination under anaesthetic and biopsy, MRI pelvis, CT, PET-CT.
• Treatment -chemoradiotherapy is first-line (preserves the sphincter; e.g. mitomycin with 5-FU or capecitabine); abdominoperineal resection for persistent or recurrent disease; local excision for very small margin tumours.
• Prevention -HPV vaccination (now offered to boys and girls, and to men who have sex with men).

Faecal Incontinence and Defecation Problems

• Faecal incontinence -common but under-reported (ask directly):
  • Causes -obstetric sphincter injury (tears, instrumental delivery -may appear years later), faecal impaction with overflow (older people -check with rectal examination), diarrhoea (IBD, IBS, bile acid diarrhoea, laxatives), anal surgery (sphincterotomy, fistulotomy, haemorrhoidectomy), rectal prolapse, neurological disease (spinal cord injury, MS, diabetes, stroke, dementia), low anterior resection syndrome, radiotherapy.
  • Assessment -history, examination (tone, squeeze, prolapse, impaction), stool chart; endoanal ultrasound and anorectal physiology tests for structural problems.
  • Management (NICE CG49) -treat the cause (impaction -disimpact and treat constipation; diarrhoea -loperamide, bile acid binders), diet and bowel habit training, pelvic floor exercises and biofeedback, anal plugs, rectal irrigation; surgery -sphincter repair, sacral nerve stimulation, rarely a stoma.
• Obstructed defecation -straining, incomplete emptying, needing to press on the perineum or vagina (digitation) -rectocele, internal intussusception, pelvic floor dyssynergia; biofeedback first; surgery for selected patients.
• Chronic constipation -mostly managed medically (see the Gastroenterology chapters); surgery is rarely needed.

Colorectal and Anal Conditions at a Glance

Condition	Key clues	Management
Colorectal cancer	Change in habit, bleeding, iron deficiency anaemia, FIT 10 or more	Colonoscopy, CT (± MRI pelvis), MDT, resection ± chemoradiotherapy
Lynch syndrome	Young colorectal and endometrial cancers in the family	MMR testing, 2-yearly colonoscopy, aspirin
FAP	Hundreds of polyps in a teenager	Prophylactic colectomy
Diverticulitis	LIF pain, fever, raised CRP	Watchful waiting or oral antibiotics; CT; drain abscesses
Colovesical fistula	Pneumaturia, recurrent UTI	CT, cystoscopy; resection
Acute severe UC	Over 6 bloody stools a day with systemic upset	IV steroids, rescue therapy, colectomy if failing
High-output ileostomy	Over 1.5–2 L/day, AKI, low Na and Mg	Restrict hypotonic fluids, ORS, loperamide, PPI
Diverticular bleed	Sudden painless large fresh bleed	Resuscitate, CT angiography, embolisation
Haemorrhoids	Painless bright red bleeding, prolapse	Fibre, banding, haemorrhoidectomy
Thrombosed external pile	Sudden very painful purple lump	Excise within 72 hours, else conservative
Anal fissure	Pain like glass on defecation, posterior midline	Softeners, GTN or diltiazem, botox, sphincterotomy
Perianal abscess	Throbbing pain, tender swelling, fever	Incision and drainage
Fistula-in-ano	Persistent discharge after an abscess	MRI, fistulotomy or seton
Pilonidal sinus	Natal cleft pits and abscesses in a young hairy man	Drainage, excision, hair removal
Anal cancer	Ulcer or mass, HPV, HIV, groin nodes	Chemoradiotherapy

Spot the Diagnosis

Clue	Diagnosis
Iron deficiency anaemia and a right iliac fossa mass in a 72-year-old	Caecal cancer
Tenesmus, bleeding and mucus with a hard mass on rectal examination	Rectal cancer -MRI pelvis
Change in bowel habit with FIT 4 but a palpable rectal mass	Refer urgently anyway
Colorectal cancer at 38 and a mother with endometrial cancer at 45	Lynch syndrome
Dark lip freckles and small bowel intussusception	Peutz–Jeghers syndrome
Desmoid tumour after colectomy for polyposis	FAP
Urgency and clustering of stools after an anterior resection	Low anterior resection syndrome
Permanent colostomy after surgery for a low rectal cancer	Abdominoperineal resection
Air in the urine and recurrent UTIs in a man with diverticulosis	Colovesical fistula
Faecal peritonitis from perforated sigmoid diverticulitis	Hinchey IV -Hartmann's procedure
Dusky, black stoma on day 1	Stoma ischaemia -urgent surgical review
Ileostomy output 3 L/day, sodium 128, AKI	High-output stoma
Frequent bowel movements and fever with a J-pouch	Pouchitis -antibiotics
Sudden painless large fresh rectal bleed in an 80-year-old with diverticulosis	Diverticular bleeding
Recurrent painless bleeding in an older person with aortic stenosis	Angiodysplasia
Painless bright red blood on the paper with prolapse that needs pushing back	Grade III haemorrhoids
Excruciating painful purple lump at the anal margin for 1 day	Thrombosed external haemorrhoid -excise
Severe pain on defecation with a posterior midline tear	Anal fissure
Multiple off-midline fissures and skin tags in a young man with weight loss	Crohn's disease
Headaches after starting a cream for a fissure	Topical GTN
Throbbing pain, fever and a red swelling beside the anus	Perianal abscess -drain
Persistent perianal discharge from an opening behind the anus	Fistula-in-ano (curved track to posterior midline -Goodsall)
Recurrent abscesses in the natal cleft of a 22-year-old	Pilonidal disease
Concentric rings protruding from the anus in an older woman	Full-thickness rectal prolapse
Anal ulcer with groin nodes in a man with HIV	Anal squamous cell carcinoma
Faecal leakage and soiling in a care home resident with a full rectum	Faecal impaction with overflow

Exam-style Scenarios

1. A 68-year-old man has 8 weeks of looser, more frequent stools and occasional dark blood mixed in. FIT result is 45 micrograms/g. Abdominal and rectal examination are normal.
Answer: Suspected colorectal cancer -urgent referral.

• Refer on the suspected cancer pathway (FIT 10 or more) for colonoscopy; FBC and ferritin.
• If a sigmoid cancer is found -CT chest, abdomen and pelvis, CEA, MDT; mismatch repair testing.
• Likely laparoscopic sigmoid colectomy or high anterior resection (enhanced recovery); adjuvant chemotherapy if node-positive; follow-up with CEA, CT and colonoscopy.

2. A 61-year-old woman has 3 days of left iliac fossa pain and fever of 38.4°C. CRP 160. CT shows sigmoid diverticulitis with a 5 cm pericolic abscess. She has no generalised peritonism.
Answer: Complicated diverticulitis (Hinchey I).

• Admit; IV antibiotics (e.g. co-amoxiclav per local policy), analgesia, fluids.
• CT-guided percutaneous drainage of the abscess (large abscess).
• Colonoscopy or CT colonography after about 6 weeks to exclude cancer; discuss elective resection if recurrent or complicated disease continues.

3. A 45-year-old man had a subtotal colectomy and end ileostomy 10 days ago for acute severe UC. His ileostomy output is 3 litres a day. He feels dizzy; creatinine has risen from 80 to 150; sodium 129; magnesium 0.5.
Answer: High-output ileostomy with dehydration, AKI and low sodium and magnesium.

• IV fluids (0.9% saline with potassium as needed) and IV magnesium; strict fluid balance and daily weights.
• Restrict hypotonic oral fluids (about 500–1,000 mL a day) and give an oral rehydration solution (St Mark's); loperamide 30–60 minutes before meals (high doses may be needed), ± codeine and a PPI.
• Exclude causes (C. difficile, partial obstruction, steroid withdrawal); involve the stoma nurse and dietitian; review diuretics and other drugs.

4. A 28-year-old woman has severe pain on opening her bowels for 3 weeks, lasting an hour afterwards, with bright red blood on the paper. Gentle parting of the buttocks shows a posterior midline tear.
Answer: Acute anal fissure.

• Stool softeners (macrogol), fibre and fluids, warm baths, simple analgesia and topical lidocaine before bowel movements.
• Topical GTN 0.4% (warn about headaches) or diltiazem 2% if not settling, for 6–8 weeks.
• Refer if not healed after 8 weeks of treatment (botulinum toxin or sphincterotomy); investigate if off-midline, multiple, or with other symptoms (Crohn's, HIV, STIs, cancer).

5. A 34-year-old man with type 2 diabetes has 3 days of throbbing pain beside his anus, worse on sitting, with a fever. There is a red, hot, tender, fluctuant swelling at 5 o'clock.
Answer: Perianal abscess.

• Incision and drainage (usually in theatre under anaesthetic); antibiotics alone are not enough -add them for cellulitis, sepsis or poor diabetic control.
• Check glucose and HbA1c; analgesia; wound care.
• Warn about a possible fistula (persistent discharge or recurrent abscess) -MRI and colorectal follow-up if this happens; consider Crohn's with recurrent or complex disease.

Key Points

• FIT of 10 micrograms/g or more with lower GI symptoms means urgent referral; refer any rectal or anal mass regardless of FIT.
• Always do a rectal examination in lower GI symptoms.
• Bowel cancer screening in England -FIT every 2 years from 50 to 74.
• Lynch syndrome -test all colorectal and endometrial cancers for mismatch repair deficiency.
• FAP -prophylactic colectomy; Peutz–Jeghers -lip freckles and intussusception.
• Right-sided cancers cause anaemia; left-sided cause bleeding, habit change and obstruction; rectal cause tenesmus.
• Rectal cancer -MRI pelvis; neoadjuvant (chemo)radiotherapy for higher-risk tumours; TME surgery.
• Abdominoperineal resection means a permanent colostomy; Hartmann's is the classic emergency operation.
• Uncomplicated diverticulitis may not need antibiotics if systemically well; drain abscesses; colonoscopy after recovery.
• Pneumaturia and recurrent UTI -colovesical fistula.
• Acute severe UC not responding to rescue therapy -subtotal colectomy with end ileostomy.
• Ileostomy -spouted, RIF, liquid; colostomy -flush, LIF, formed.
• High-output stoma -restrict hypotonic fluids, oral rehydration solution, loperamide, replace magnesium.
• Lower GI bleeding with shock and high urea -consider an upper GI source; CT angiography for active bleeding.
• Internal piles are painless; thrombosed external piles are very painful -excise within 72 hours.
• Fissures are usually posterior midline; off-midline suggests Crohn's, HIV, syphilis or cancer.
• Perianal abscess -incision and drainage, not antibiotics alone; fistulas may follow.
• Anal cancer -HPV and HIV; chemoradiotherapy is first-line.
• Ask directly about faecal incontinence; check for impaction with overflow.

Guidelines and Further Reading

• NICE NG12: Suspected cancer -recognition and referral; NICE DG56: Quantitative faecal immunochemical testing
• NICE NG151: Colorectal cancer
• BSG, ACPGBI and UKHSA: Post-polypectomy and post-colorectal cancer resection surveillance guidelines
• BSG and ACPGBI: Guidelines for the management of hereditary colorectal cancer
• NICE NG147: Diverticular disease
• BSG: Consensus guidelines on the management of inflammatory bowel disease in adults
• BSG: Diagnosis and management of acute lower gastrointestinal bleeding (Oakland score)
• ACPGBI: Position statements and guidelines on haemorrhoids, anal fissure, anal fistula and pilonidal disease
• NICE CG49: Faecal incontinence in adults
• NICE CKS: Haemorrhoids; Anal fissure
• BNF -for current doses