Water soluble contrast is administered via a rectal catheter.  Although a fistula may be identified on CT, including with rectal contrast distilled on table, traditional fluroscopy remains the premier modality, offering dynamic assessment.

Contrast promptly fills the vagina, in keeping with a rectovaginal fisula - the commonest form of colovesical fistula.

The commonest causes are; diverticular disease, malignancy and following pelvic radiation.  A diverticulum can be seen in this case.