Small bowel is involved in 80% of cases.

Disease is confined to the colon.

Rectum is often spared; colonic involvement is usually right-sided.

Rectum is invariably involved; colonic involvement is usually left-sided.

Gross rectal bleeding is rare, except in 75‒85% of cases of Crohn colitis.

Gross rectal bleeding is always present.

Fistula, mass, and abscess development is common.

Fistulas do not occur.

Perianal lesions are significant in 25‒35% of cases.

Significant perianal lesions never occur.

On x-ray, bowel wall is affected asymmetrically and segmentally, with skip areas between diseased segments.

Bowel wall is affected symmetrically and uninterruptedly from rectum proximally.

Endoscopic appearance is patchy, with discrete ulcerations separated by segments of normal-appearing mucosa.

Inflammation is uniform and diffuse.

Microscopic inflammation and fissuring extend transmurally; lesions are often highly focal in distribution.

Inflammation is confined to mucosa except in severe cases.

Epithelioid (sarcoid-like) granulomas are detected in bowel wall or lymph nodes in 25‒50% of cases (pathognomonic).

Typical epithelioid granulomas do not occur.