Skip granulomatous lesions are seen in -
Features of CD 

Ileum is involved most commonly; therefore, CD is also known as terminal ileitis.
In the affected segment, mesentric fat wraps around the bowel surface → creeping fat.
The intestinal wall is rubbery and thick, as a consequence of edema, 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 adjacent uninvolved bowel. When multiple bowel segments are involved, the intervening bowel is normal → skip lesions.
There are serpentine linear ulcer along the axis of 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 bowel wall.
Sarcoid like noncaseating granulomas may be present in all tissue layers.
Neutrophilic infiltration into the crypts results in formation of crypt abscess.
Fibrosis of the submucosa, muscularis propria, and mucosa enentually leads to stricture fromation.
There is an increased incidece of cancer of GIT in patints with long- standing CD, but the risk of cancer in CD is considerably less then in patients with chronic UC.
Screening test is presence of anti-Saccharomyces cerevisae antibody (ASCA). Antibody formation is common against cell wall of yeast, Saccharomyces cerevisae in patients of CD.
To confirm the diagnosis endoscopy is done so that direct visualization of the lesion can be done and even a biopsy can be done if needed.
Ulcerative colitis
Crohn's disease
Whipple's disease
Reiter's disease