Skip granulomatous lesions are seen in –
Features of CD

In the affected segment, mesenteric fat wraps around the bowel surface → creeping fat
The intestinal wall is rubbery and thick, as a consequence of oedema, inflammation, fibrosis, and hypertrophy of the muscularis propria → lumen is almost always narrowed → string sign on barium meal.
A classic feature of CD is the sharp demarcation of diseased bowel segments from adjucent uninvolved bowel.
When multiple bowel segments are involved, the intervening bowel is normal to skip lesions.
There is serpentine linear ulcer along the axis of the bowel.
As the intervening mucosa tends to be relatively spared, the mucosa acquires a coarsely textured → Cobblestone appearance.
Narrow fissures develop between the folds of the mucosa.
Fissures can penetrate deeply through the bowel wall and leading to bowel adhesions and serositis.
Further extension of fissures leads to fistula or sinus tract formation.
There is transmural inflammation affecting all layers of the bowel wall.
Sarcoid-like noncaseating granulomas may be present in all tissue layers.
Neutrophilic infiltration into the crypts results in the formation of crypt abscess.
Fibrosis of the submucosa, muscular propria, and mucosa eventually leads to stricture formatting.
There is an increased incidence of cancer of GIT in patients with long-standing CD, but the risk of cancer in CD is considerably less than in patients with chronic UC.
Ulcerative colitis
Crohn's disease
Whipple's disease
Reiter's disease