Seeras KK, Lopez PP. Fistula, colovesicular. StatPearls 2018; .
A fistula is an irregular connection between two epithelialized surfaces. It can be classified or named based on which organs it connects. A connection between the colon and the bladder is termed a "colovesicular fistula." To understand this disease process and the operative planning, clinicians must understand the intricate anatomy of the pelvis and the organs it contains. Anatomy Sigmoid Colon Sigmoid colon begins as the descending colon crosses the pelvic brim. The sigmoid colon is relatively mobile compared to the more fixed descending colon. Sigmoid colon varies in length ranging from 15 to 50 cm (average of 38 cm). The rectosigmoid junction (defined by  located at the level of the sacral promontory or  where the taeniae converge) marks the transition from the sigmoid colon to the rectum. The rectum is bordered anteriorly by Denonvilliers' fascia, which separates the rectum from the prostate/seminal vesicles in men, and separates the rectum from the vagina in women. Histologically the colon has four layers, from deep to superficial: 1. Mucosa (columnar epithelium). 2. Submucosa (contains most of the collagen within the bowel wall and is the strength layer). 3. Muscularis Propria (contains inner circular and outer longitudinal layers) - the outer longitudinal layer is separated into the three taenia coli on the colon. 4. Serosa Blood Supply The blood supply to the rectum and sigmoid colon is primarily from the inferior mesenteric artery (IMA). IMA gives off the left colic to the ascending colon, sigmoidal branches to the sigmoid colon and the superior rectal artery to the proximal rectum. The terminal branches of these arteries form an anastomotic arcade with the adjacent branches. Urinary Bladder The urinary bladder is situated in the retropubic space (Retzius) and is considered extra-peritoneal. In a male patient, the posterior bladder wall lies adjacent to the anterior sigmoid colon and rectum. In the female patient, the superior bladder abuts the lower uterus, and the bladder base sits adjacent to the anterior portion of the vaginal wall. The uterus separates the colon from the bladder making fistula between them much less common in females. Ureters The ureters leave the renal pelvis and course anterior to the psoas muscle. They diverge medially at the pelvic brim crossing anterior to the iliac vessels near their bifurcation. They course along the pelvic sidewall and pass under the uterine artery in women and finally enter the bladder at the lateral aspect of the base.