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Don't mix these up for NEET PG: Crohn disease vs ulcerative colitis

PathologyPublished 30 October 2026 · Recallab

A high-yield NEET PG pair. Both are chronic inflammatory bowel diseases with diarrhoea, and the questions separate them on three things: where the disease is, how deep it goes, and what surgery can do.

Recallab Scroll short for NEET PG: Crohn disease or ulcerative colitis, 39 seconds.

Crohn disease vs ulcerative colitis: side by side

	Crohn disease	Ulcerative colitis
Distribution	Mouth to anus, skip lesions	Colon and rectum, continuous from the rectum upwards
Depth	Transmural	Mucosa and submucosa
Granulomas	Non-caseating, in about half	Absent
Mucosa	Deep linear ulcers, cobblestoning	Red granular mucosa, pseudopolyps
Fistulas and strictures	Common	Rare
Smoking	Worsens it	Protective
Surgery	Can recur in the remaining bowel	Proctocolectomy cures the bowel disease

Depth explains the complications. Inflammation through the whole wall of the bowel is what lets Crohn disease form fistulas, strictures, abscesses and perianal disease. Ulcerative colitis stays in the lining, so it bleeds instead, and rectal bleeding is characteristic.

In India, the look-alike that matters most for Crohn disease is intestinal tuberculosis. Caseating granulomas and acid-fast bacilli separate them, and the distinction is consequential, because steroids given for tuberculosis are dangerous.

The one trap

The trap is treating any gap as Crohn disease. Skip lesions are the classic Crohn sign, but ulcerative colitis has recognised exceptions. An isolated periappendiceal caecal patch can accompany otherwise typical distal colitis, and backwash ileitis can carry it a short way into the terminal ileum. Neither alone overturns ulcerative colitis.

The reverse trap is crypt abscesses. They occur in both diseases, so they do not prove ulcerative colitis; how deep the inflammation goes is what separates the two.

Try it: say it once before the questions: Crohn roams the gut, through the whole wall; colitis stays in the colon, in the lining.

Pattern and antibodies

Recallab example 1 · two bowel maps, two antibody cards

Two patients with months of diarrhoea are drawn in the figure: for each, the bowel actually involved and a section of the wall at the worst point. Beneath them are the two antibody cards from these patients, which have not been matched to them. Which card belongs to patient 1?

Look first: first name each disease from its map and wall section, then match the antibody that leans towards it.

Two outlines of the whole gut, labelled Patient 1 and Patient 2. In patient 1 the diseased segments are shaded in patches with normal bowel between them, one in the last part of the ileum and two in the colon, and the wall section shows inflammation through all the layers with a small granuloma in the deepest layer. In patient 2 the shading is continuous from the anus upwards through the left colon, and the wall section shows inflammation confined to the lining. Beneath, two unmatched result cards: Card A, antibody to a mannan antigen, positive; Card B, neutrophils with staining around the nucleus, positive. — Recallab question 58316. Two bowel maps with wall sections, and two unmatched antibody cards.

ANeither card
BCard A
CBoth cards
DCard B

Show the answer and explanation

Answer: B. Card A

B. Card A, the antibody to a mannan antigen of yeast (anti-Saccharomyces cerevisiae antibody). Patient 1 has skip lesions, inflammation through the whole wall and a granuloma: Crohn disease, in which this antibody is commoner. Patient 2 has continuous disease from the anus upwards with only the lining involved: ulcerative colitis, in which the perinuclear neutrophil staining pattern is commoner. Both antibodies are missing in many patients, so a negative card proves nothing. They support a diagnosis without settling it; the biopsy decides.

Why the other options lose: neither card (A) ignores that the mannan antibody goes with the patchy transmural disease of patient 1. Both cards (C) would give one patient two antibodies that track different diseases. Card B (D) is the perinuclear pattern, which belongs with the continuous mucosal disease of patient 2.

Recallab question 58316 · Pathology › GIT · reference: Robbins, Cotran & Kumar Pathologic Basis of Disease

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The long-standing colon

Recallab example 2 · two contrast enemas

Two contrast enema outlines are drawn in the figure, one from each of two patients who have had diarrhoea for several years. Which feature, rather than the ulceration itself, marks long standing ulcerative colitis?

Look first: compare the walls: which outline has lost its indentations, and does the change run without a break from the rectum?

Two contrast enema outlines of the whole large bowel, numbered 1 and 2. Outline 1 has regular rounded indentations along both walls of every segment and a normal long looping course. Outline 2 has no indentations anywhere: both walls run smooth and parallel from the rectum upwards, the bowel is shorter and straighter with the flexures lower and closer together, and the calibre is evenly narrowed, continuously from the rectum with no normal segment. — Recallab question 58246. Two contrast enema outlines from two patients with years of diarrhoea.

AShort shouldered narrowing
BSmooth shortened featureless colon
CSkip lesions sparing the rectum
DRegular haustral indentations

Show the answer and explanation

Answer: B. Smooth shortened featureless colon

B. Smooth shortened featureless colon. Outline 2 runs smooth from the rectum to the caecum with no indentations. The haustra are lost because the muscle coat has shortened and thickened, and the flexures sit lower and closer together because the whole colon is shorter. No normal segment interrupts the change, so it is continuous rather than patchy: long-standing ulcerative colitis. Outline 1 is the normal colon, drawn for comparison. The ulceration itself is shown far better at endoscopy.

Why the other options lose: a short shouldered narrowing (A) is the appearance of a tumour. Skip lesions sparing the rectum (C) belong to Crohn disease. Regular haustral indentations (D), as in outline 1, are the normal appearance.

Recallab question 58246 · Radiology › GIT · reference: Bailey & Love's Short Practice of Surgery

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What surgery can cure

Recallab example 3 · two colectomy specimens

Two resected colons from patients with chronic diarrhoea and pain are drawn in the figure. In which patient does removing the colon and rectum cure the bowel disease?

Look first: name each specimen, then ask which disease stays inside the bowel that was removed.

Two opened lengths of large bowel with the rectum at the lower end. Specimen 1: disease beginning at the rectum and running continuously upwards to a sharp line, with a red granular mucosa, scattered pseudopolyps and a thin wall. Specimen 2: segments of disease separated by normal bowel, the diseased mucosa cobblestoned by deep linear ulcers, a thickened wall with one stricture, and fat creeping around the outer surface. — Recallab question 55455. Two opened colectomy specimens laid side by side.

ANeither patient
BBoth patients
CSpecimen 2
DSpecimen 1

Show the answer and explanation

Answer: D. Specimen 1

D. Specimen 1. Its disease starts at the rectum and runs continuously upwards, with a red granular mucosa and pseudopolyps: ulcerative colitis. Ulcerative colitis is confined to the colon and rectum, apart from backwash ileitis, so removing them removes all the diseased bowel. Specimen 2 has skip lesions, cobblestoning, a thickened wall with a stricture and creeping fat: Crohn disease, which can return anywhere from mouth to anus. The usual operation for ulcerative colitis is a restorative proctocolectomy with an ileal pouch, with a permanent ileostomy when a pouch is not suitable.

Why the other options lose: neither patient (A) is wrong because ulcerative colitis does not return once the colon and rectum are gone. Both patients (B) and specimen 2 (C) are wrong because Crohn disease recurs in the remaining bowel, often at the anastomosis.

Recallab question 55455 · Pathology › GIT & Hepatobiliary Pathology · reference: Robbins, Cotran & Kumar Pathologic Basis of Disease

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Drawn from questions #58316, #58246, #55455, #74170, #50123 in the Recallab bank, each with its own verified answer and current-edition reference. Last reviewed 30 October 2026.