I had a abdomen ct scan performed for kidney stones and a relative change in sigmoid caliber was noted, with no evidence of mass lesion. a follow up colonoscopy was recommended which did not reveal any findings. are there common explanations/causes?

CT scan for kidney stone is done without preparation so the sigmoid caliber may be not correctly read because the content in the sigmoid at the time. Whatever, I think it is not worth your concern if direct visualization is normal by colonoscopy. Take care.

Narrowing of the sigmoid can have several causes. One would be a resolved episode of ischemic colitis others could be an auto immune disorder like Crohn’s disease or ulcerative colitis. Or it may just be a narrow variant type. Recommend reviewing this with the physician, who ordered and also the Doctor Who did the colonoscopy