Conversely, diverticular disease is the most common cause of colovesical fistulas, followed by colon cancer and Crohn's disease. Colovesical fistulas are much less common in women than in men because the uterus is interposed between the sigmoid and the bladder. Patients with bladder fistulas usually present with recurrent polymicrobial urinary infections, pneumaturia, or both. Fistulas may also involve other parts of the colon, the small bowel, the uterus, or the vagina. Colocutaneous fistulas are unusual and generally occur after surgery for diverticulitis.
Colovesical fistulas are difficult to visualize.
However, CT is sensitive for the detection of air in the bladder, which, in the absence of previous bladder catheterization or cystoscopy, is virtually diagnostic of an enterovesical fistula. The detection of bladder wall thickening adjacent to an area of diverticulitis supports the diagnosis. Cystoscopy frequently reveals focal mucosal inflammation in the area of the fistula, and contrast cystography may opacify the fistula. Barium enema often fails to opacify a colovesical fistula, although secondary changes of diverticulitis are often apparent. Colonoscopy is necessary to exclude colon cancer and inflammatory bowel disease.