Collar button ulcer is found in?

Ans. is 'd' i.e., All of the above * "Collar button ulcers", a radiological sign, are manifestations of inflammatory processes within the bowel.* These deep ulcerations are classically seen in the colon associated with active ulcerative colitis. The collar button appearance is formed by mucosal ulceration with associated undermining of the ulcer's edge by lateral submucosal extension. Vertical penetration into the bowel wall is limited due to the resistance of the underlying muscularis mucosa, thus resulting in the discoid collar button appearance of these ulcers.* Collar button ulcers have also been observed in the setting of other inflammatory bowel processes, such as Crohn's disease, ischemic colitis, and shigellosis.