What are the characteristic features of Crohn's disease?

Characteristic Features of Crohn's Disease

The three characteristic features of Crohn's disease are: (1) fistulous tracts may occur as disease complications, (2) inflammation affects all layers of the intestinal tract wall (transmural), and (3) the disease may be limited to the small intestine.

Transmural Inflammation

• Crohn's disease is characterized by transmural inflammation that extends through all layers of the intestinal wall, distinguishing it fundamentally from ulcerative colitis which remains confined to the mucosa 1, 2.
• This full-thickness involvement of the bowel wall is a defining pathologic feature that drives the development of stricturing and penetrating complications 3.
• The transmural nature of inflammation can be visualized on cross-sectional imaging as mural thickening with hyperenhancement extending through the entire bowel wall 3.

Penetrating Complications and Fistulous Tracts

• Fistulas represent a hallmark complication of Crohn's disease, arising from the transmural inflammatory process that creates abnormal connections between bowel loops or to adjacent structures 3.
• Fistulas typically arise from within or just proximal to strictures and can be simple (single tract) or complex (multiple tracts forming an asterisk or "clover-leaf" appearance) 3.
• Approximately one-quarter of perianal fistulas present at or before the time of Crohn's disease diagnosis, with incidence varying by age and disease location 3.
• CT and MR enterography demonstrate moderately high accuracy for detecting penetrating complications including fistulas, inflammatory masses, and abscesses 3.

Disease Distribution and Location

• Crohn's disease can affect any part of the gastrointestinal tract from mouth to anus, with the terminal ileum being the most commonly affected site 4, 2.
• The disease may be limited to the small intestine alone (25% ileitis only), colon alone (25% colitis only), or both (50% ileocolitis) 2.
• This skip pattern with potential small bowel-only involvement contrasts sharply with ulcerative colitis, which is limited to the colon and begins at the rectum with continuous proximal extension 1.

Why the Other Options Are Incorrect

Regarding Remission Rates

• The statement that "90% of patients will not have significant remission" is incorrect and overly pessimistic 2, 5.
• Crohn's disease follows a chronic relapsing-remitting course, with periods of flares alternating with remissions 2, 6.
• Current therapeutic strategies with biologics and immunomodulators can achieve deep and long-lasting remission in many patients, particularly with early aggressive treatment 7, 5.

Regarding Pattern of Inflammation

• The statement that "inflammation is diffuse and continuous" is characteristic of ulcerative colitis, not Crohn's disease 3, 1.
• Crohn's disease demonstrates patchy, discontinuous, segmental inflammation with skip lesions, meaning areas of normal bowel separate inflamed segments 3, 1, 2.
• Asymmetric involvement is typical, particularly along the mesenteric border, rather than the circumferential continuous pattern seen in ulcerative colitis 3, 4.
• The European consensus on histopathology specifically identifies focal (discontinuous) crypt architectural irregularity and chronic inflammation as distinguishing features of Crohn's disease versus the diffuse (continuous) pattern in ulcerative colitis 3.