Figure 10b. Ileovesical fistulas. (a) Cystogram of a patient with a history of abdominal surgery shows leakage of contrast material from the bladder (B) into the ileum (I) and proximal colon, thus indicating the diagnosis. (b) Image from a small-bowel follow-through study, obtained in a patient with a fistula due to Crohn disease, shows contrast material in the bladder (B), which is the key diagnostic finding.