A 74-year-old lady with a past history of a right breast infiltrating ductal carcinoma on chemotherapy, had presented with chief complaints of passing foul smelling urine, passage of 'gas' in the urine and pelvic pain for 1 month. She reported no history of trauma or recent pelvic surgery.
Plain CT of the abdomen [axial (Fig.1a) and coronal (Fig.1b) sections] done in view of her current complaints, showed a collection located postero-superior to the urinary bladder, communicating with the bladder through a 12 mm defect. Multiple diverticuli were noted involving the sigmoid colon (Fig. 1c). In addition, urinary bladder intraluminal air and affected segment of the sigmoid colon showed wall thickening (Fig. 1d, e).
On rectal administration of contrast (Fig. 2a, b), contrast was noted to fill the collection and urinary bladder. The source of the contrast extravasation was through sigmoid colon defects noted in its inferior wall (Fig.2c).
Diverticulosis of the colon are acquired herniations of the mucosa and submucosa through the muscle layers of its walls. Diverticulosis may be seen anywhere along the colon, with the sigmoid colon being the commonest site.  Diverticulosis simply means the presence of diverticula, while the term ‘diverticulitis’ is used only when there is proven inflammation associated with diverticula. 
Colovesical fistula (CVF), is an abnormal communication between the urinary bladder and large intestine, that can be caused by various inflammatory and neoplastic conditions, among which sigmoid diverticulitis remains the most recognised cause of this pathology. The underlying mechanism is either a direct extension of a ruptured diverticulum or erosion of a diverticular abscess into the bladder.  Patients usually present with complaints of pneumaturia (50-70%), faecaluria (50%), increased frequency and urgency of urination, suprapubic pain and haematuria. [4, 5, 6]
CT is the most sensitive imaging modality for evaluating CVFs with a diagnostic accuracy of 60-100%. Most common findings include- air/gas in lumen of the bladder, local thickening of the bladder wall, thickening of the adjacent bowel wall, adherence of soft tissue masses outside the wall of the bladder, and adjacent abscesses when present. [6, 7]
Potential benefits of rectal contrast for diverticulitis in general include better visualisation of colonic wall and diverticula. For CVF in particular, use of rectal contrast can help identify and confirm a fistula tract. Rectal contrast has a benefit over oral contrast in particular when problems are expected in the distal colon, as the former would induce unnecessary delays, particularly in an emergency setting. [8, 9]
The role of MRI is less well established, with only one study demonstrating a sensitivity and specificity of 100% in identifying CVFs accurately in 18 patients. 
The most widely accepted treatment for CVFs is a surgical approach by removal of the fistula and the diseased segment of the colon to prevent recurrence.  Our patient underwent drainage of the abscess, and repair of the colovesical fistula followed by diversion loop colostomy.
Written informed patient consent for publication has been obtained.
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