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.
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:
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.
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.
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.
Generally, causes of fistulas can be remembered with the simple mnemonic FRIENDS. Foreign body, Radiation, Inflammatory Bowel Disease, Epithelialization, Neoplasm, Distal obstruction, Sepsis (infection).
The most common cause of colovesicular fistulas is the sequelae of complicated diverticulitis and accounts for over two-thirds of cases . The second most common cause is a malignancy in 10% to 20% of cases and is usually adenocarcinoma of the colon. Crohn’s colitis is the third most common cause (5% to 7% of cases) and usually is a result of long-standing disease .
Other less common causes of colovesicular fistulas are iatrogenic injury secondary to surgery or procedures, pelvic radiation, abdominal trauma, and tuberculosis (TB).
Diverticular disease, the most common etiology for the development of colovesicular fistulas, is a very common disease of western society. Patients older than 60 years of age have a 30% chance of developing diverticulosis and patients older than 80 years of age have an approximately 70% chance. Fifteen percent to 25% of patients with diverticulosis will develop diverticulitis in their lifetime , however in a 2013 retrospective review they demonstrated only a 4% lifetime risk . The incidence of having a colovesicular fistula in the presence of diverticular disease is 2% to 23% .
The average age at presentation for colovesicular fistulas is between 55 and 75 years of age. There is a male predominance secondary to females having a uterus , and the majority of females that do develop colovesicular fistulas have had a prior hysterectomy .
The pathophysiology leading to the development of colovesicular fistulas can differ depending on the specific etiology.
The pathophysiology behind colovesicular fistula formation begins with the formation of diverticula in the sigmoid colon. These are false diverticula characterized by the protrusion of the mucosa and submucosa through the muscularis propria at the point of entry of the vasa recta (blood supply to the mucosa/submucosa and a point of relative weakness in the colonic wall on the mesenteric side). These outpouchings occur mainly secondary to high intraluminal pressure which is exacerbated by muscularis hypertrophy, altered colonic motility, and narrowing of the lumen. The theory that fecaliths obstruct the lumen of the diverticula leading to distention and perforation is now out of date. The more reasonable theory is that increased intraluminal pressure with abnormal peristalsis directs force radially into the diverticula and cause micro or macro perforations which are characterized as diverticulitis. This may result in a diverticular abscess or phlegmon that ruptures into an adjacent organ (i.e., the bladder) and creates a fistula.
The most common malignant etiology of colovesicular fistulas is colonic adenocarcinoma directly invading the urinary bladder and forming an abnormal connection.
Long-standing transmural inflammation results in the formation of fistulae between the colon and other organs (bladder, bowel, uterus, vagina). Up to 35% of patient with Crohn’s disease develop fistulas. Most commonly these involve the small intestine leading to entero-entero, entero-colonic, ileo-sigmoid, and entero-cutaneous fistulae, among others. Rarely, long-standing Crohn’s colitis of the sigmoid colon can lead to colovesicular or colovaginal fistulas.
Histologic examination is also dependent on etiology.
Crohn’s Disease: Lymphoid aggregates, transmural inflammation, non-caseating granulomas
Adenocarcinoma: Likely inflammatory aggregates adjacent to the tumor present
Diverticular Disease: Hypertrophy of the muscle layers, luminal narrowing, and an excess of mast cells within the bowel wall layers
Signs and Symptoms
A patient can present with recurrent urinary tract infections (usually third MC symptoms)
More specifically they present with pneumaturia and/or fecaluria (air and/or stool in urinary stream, usually at the end of urination). This is present in about 70% to 90% (pneumaturia) and 50% to 70% (fecaluria) of patients with CVF . Virtually pathognomonic for CVF. Clinicians must rule out other causes of pneumaturia such as recent bladder instrumentation or emphysematous cystitis/UTI with gas-forming organisms.
Less frequently, patients can experience dysuria, hematuria, urgency, frequency, suprapubic pain.
Interestingly less than 50% of patients with diverticular CVF report a history of diverticulitis .
The goals of the evaluation are to confirm the diagnosis and determine the underlying etiology.All patients get a CT scan and lower endoscopic evaluation .
The first and best test is a CT scan with oral or rectal contrast without IV contrast (greater than 90% accurate) . This will show contrast or air in the bladder with colonic and vesicular wall thickening. It may not show the actual fistula tract but accurately predicts the location. CT scan is also useful for delineating anatomy, discovering tumors, and helps determine underlying etiology.
Colonoscopy has a low sensitivity (11% to 89%) for detecting fistula tract. It is used to rule out malignancy preoperatively .
This test also low sensitivity (less than 50%) versus a CT scan for detecting CVF. Clinicians usually do not see fistula tract but see edema at the site. It is indicated if there is suspicion for a malignant fistula of the bladder, for example, a history of bladder cancer, bladder mass on CT, or an absence of colonic pathology.
A barium enema is less commonly done today; CT and endoscopy have largely replaced it. It can be useful in the diagnosis of CVF (only 30% Sn) and underlying etiology, for example, colon cancer or diverticulosis.
Poppy Seed Test
In this test, the patient ingests poppy seeds, and their urine is examined in 48 hours. It has a 100% detection rate of CVF but provides little information regarding disease location or etiology .
MRI is useful in complex fistulas in Crohn’s patients; high-costplain radiography.
If there is clinical evidence of infection, treat with systemic antibiotics.
For surgically unfit patients or patients with inoperable metastatic disease (not a surgical candidate), the following are appropriate:
Experimental treatments include endoscopic fibrin glue injection  into the fistula tract (used for benign fistula) as well as a covered colonic stent (useful for concomitant malignant fistula and stricture) .
Surgically fit patients should have operative repair of CVF (open or minimally invasive).
All patients will require a bladder Foley catheter for a period of 7-10 days postoperatively .
A purely diverting ostomy to divert the fecal stream from the CVF has fallen out of favor secondary to poor resolution rates, persistent urinary tract infections, and high recurrence rates.
Few other processes present with pneumaturia. These include:
The etiology of the colovesicular fistula must be clear before treatment. This is evaluated with a CT scan of the abdomen/pelvis first, followed by a colonoscopy. If there is suspicion for bladder malignancy, then a cystoscopy is warranted.
The prognosis of colovesicular fistulas is largely based on the underlying etiology. The most common cause of CVF is a benign diverticular disease with a favorable prognosis. Recent publications have shown that there is little to no difference in rates of septicemia, renal failure, and mortality when comparing surgical treatment to the nonsurgical, conservative management of CVF .
Complications after elective colon resection for colovesicular fistula :
Foley should remain in the patient for a total of 7 to 10 days.
Many centers around the world are implementing enhanced recovery after surgery programs which has shown to be safe while shortening the average length of stay, which is now 3 days for elective colon resections.
Some consultants that may be needed in the management of a patient with colovesicular fistula involve:
The management of a colovesical fistula is best done with a multidisciplinary team of a general surgeon, urologist, oncologist, and colorectal surgeon. However, since many patients do have a urinary catheter left in place, the role of the nurse is vital. The nurse will monitor the urine and order cultures when an infection is suspected. If the patient has hematuria, the surgeon and radiologist need to be notified for imaging studies. Patients need to be educated about the symptoms of a colovesical fistula in case there is a recurrence. If the cause was from diverticulitis, a dietary consult is recommended to educate the patient on the importance of a high-fiber diet. Finally, the nurse should ensure that the patient has prophylaxis against deep vein thrombosis and is ambulatory. (Level V)
For patients who undergo repair of the fistula from benign causes, the outcomes are excellent. However, if the cause is related to radiation or a malignancy, the outcomes are guarded. Other studies reveal that a single stage repair is not associated with worse outcomes compared to a multistage repair. The overall prognosis is worse for patients with a colonic malignancy and before a repair is even undertaken, a metastatic workup is necessary. The highest risk of recurrence is following radiation. When the fistula persists, the quality of life is also poor. (Level V)