IBD — MRCS Part B Surgical pathology

A pathology station on inflammatory bowel disease, starting from an acute presentation and working through Crohn's disease and ulcerative colitis to the surgery each one needs.

Assessment and acute investigation

History of the stool frequency, blood and mucus, pain, weight loss and extra-intestinal symptoms; examination for dehydration, fever, tachycardia, abdominal tenderness and distension, and the perianal disease of Crohn's. Bloods: full count for anaemia and a raised white count, urea and electrolytes for dehydration and hypokalaemia, CRP and ESR, albumin, liver function, iron, B12 and folate, a group and save. Stool culture and Clostridioides difficile toxin to exclude infection, faecal calprotectin, an erect chest and supine abdominal film for toxic dilatation and perforation, and a flexible sigmoidoscopy with biopsies once the patient is stable. CT if perforation, abscess or obstruction is suspected.

Crohn's disease

A chronic transmural granulomatous inflammation that can affect any part of the gut from mouth to anus, most often the terminal ileum and the colon, in patches with normal bowel between (skip lesions). Macroscopically: a thickened, narrowed, hose-pipe bowel with fat wrapping round it, deep serpiginous ulcers between oedematous mucosa giving a cobblestone surface, fissures, fistulae and strictures. Microscopically: transmural inflammation with lymphoid aggregates, non-caseating granulomas in about half, fissuring ulcers and fibrosis, with the goblet cells preserved. It presents with diarrhoea, abdominal pain, weight loss, a right iliac fossa mass, perianal fistulae and abscesses, mouth ulcers, and in children failure to grow. Extra-intestinal features: arthritis and sacro-iliitis, erythema nodosum and pyoderma gangrenosum, uveitis and episcleritis, gallstones and renal stones, and primary sclerosing cholangitis (rarer than in colitis). Complications: strictures and obstruction, fistulae to skin, bladder, vagina or other bowel, abscesses, perforation, malabsorption and B12 deficiency after ileal disease or resection, and a raised risk of small bowel and colonic cancer.

A new diagnosis is managed by a gastroenterologist with the surgeon involved from the start: stop smoking, induce remission with steroids (or exclusive enteral nutrition in children), maintain it with azathioprine or methotrexate, and escalate to anti-TNF or other biologics for resistant or fistulating disease; treat the nutrition and the anaemia. Surgery is for the complications, not the disease, and takes as little bowel as possible: a limited ileocaecal resection, stricturoplasty, drainage of abscesses and setons for fistulae. About three-quarters of patients have an operation within twenty years.

Acute severe colitis

Six or more bloody stools a day with fever, tachycardia, anaemia or a raised ESR, the Truelove and Witts criteria, is an emergency: admit, resuscitate with fluids and replace potassium, intravenous hydrocortisone, thromboprophylaxis, stool cultures, daily bloods and abdominal films, and a joint medical and surgical review every day. Failure to improve by day three (a stool frequency above eight, or a CRP above 45 with three to eight stools) means rescue therapy with ciclosporin or infliximab, and a colectomy if that fails within a few days or at any point if the colon dilates beyond 6 cm, perforates or bleeds uncontrollably. The operation is a subtotal colectomy with an end ileostomy, leaving the rectum for later.

Ulcerative colitis

A diffuse mucosal inflammation confined to the colon, starting at the rectum and extending proximally without skipping, and stopping at the ileocaecal valve except for backwash ileitis. Macroscopically: a red, granular, friable mucosa with contact bleeding, shallow ulcers, and pseudopolyps of surviving mucosa between them; a chronically diseased colon is shortened, narrowed and featureless. Microscopically: inflammation limited to the mucosa and submucosa, crypt abscesses and crypt distortion, goblet cell depletion, and no granulomas. Treatment is 5-aminosalicylates, topically for proctitis and orally for more extensive disease, steroids for flares, thiopurines or biologics for maintenance in those who relapse, and surveillance colonoscopy from eight to ten years after diagnosis because the cancer risk rises with extent and duration. Colectomy cures the bowel disease: a panproctocolectomy with an end ileostomy, or a restorative proctocolectomy with an ileal pouch.

Crohn's disease against ulcerative colitis

Crohn's: anywhere in the gut, patchy, transmural, granulomas, fistulae and strictures, perianal disease, smoking makes it worse, surgery does not cure it. Colitis: colon and rectum only, continuous from the rectum, mucosal, crypt abscesses, bleeding and urgency, smoking oddly protects, colectomy cures it. Both share the arthritis, skin, eye and liver associations, and both raise the risk of colorectal cancer.

Vitamin B12

Freed from food by gastric acid and pepsin, bound first to haptocorrin from the saliva, released from it by pancreatic enzymes in the duodenum, and then bound to intrinsic factor from the gastric parietal cells; the complex is absorbed by receptors in the terminal ileum alone. So B12 deficiency, with its macrocytic anaemia and neuropathy, follows a total gastrectomy, pernicious anaemia, and disease or resection of the terminal ileum, which is why patients who have had an ileocaecal resection for Crohn's disease need injections for life.