Colovesical Fistula

Etiology

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 [1]. 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 [1].

Other less common causes of colovesicular fistulas are iatrogenic injury secondary to surgery or procedures, pelvic radiation, abdominal trauma, and tuberculosis (TB).

Epidemiology

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 [2], however in a 2013 retrospective review they demonstrated only a 4% lifetime risk [3]. The incidence of having a colovesicular fistula in the presence of diverticular disease is 2% to 23% [4].

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 [5], and the majority of females that do develop colovesicular fistulas have had a prior hysterectomy [6].

Pathophysiology

The pathophysiology leading to the development of colovesicular fistulas can differ depending on the specific etiology.

Diverticular Disease

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 The theory that fecaliths obstruct the lumen of the diverticula leading to distention and perforation is now out of date.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.

Malignancy

The most common malignant etiology of colovesicular fistulas is colonic adenocarcinoma directly invading the urinary bladder and forming an abnormal connection.

Crohn’s Disease

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.

Histopathology

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

History and Physical

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 [7][4][8]. 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 [9].

Evaluation

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 [10].

CT Scan

The first and best test is a CT scan with oral or rectal contrast without IV contrast (greater than 90% accurate) [1]. 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

Colonoscopy has a low sensitivity (11% to 89%) for detecting fistula tract. It is used to rule out malignancy preoperatively [10].

Cystoscopy 

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.

Barium Enema

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 [4].

MRI

MRI is useful in complex fistulas in Crohn’s patients; high-costplain radiography.

Treatment / Management

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:

• Conservative management: Historically believed to not be an option due to high rates of urosepsis and mortality; however, recent analyses of the data have shown that there are minimal morbidity and mortality associated with nonoperative management [11][12].

• Experimental treatments include endoscopic fibrin glue injection [13] into the fistula tract (used for benign fistula) as well as a covered colonic stent (useful for concomitant malignant fistula and stricture) [14].

(B2)

Surgically fit patients should have operative repair of CVF (open or minimally invasive).

• Most patients should receive a single-stage operation (no increased risk in morbidity or mortality compared to staged operations) [15]: Mobilize left colon, separate adherent sigmoid off the bladder, inject methylene blue in Foley to identify the bladder hole, close of bladder hole if big enough to warrant it, resect diseased colon with primary anastomosis, interpose omentum between bladder and colon. If due to malignant disease, require debridement of involved bladder and lymph node harvest
• Patients who are at high risk for an anastomotic leak, for example, a contaminated field with feces or abscess, current steroid use, history of pelvic radiation, hemodynamic instability, should get a staged operation. First stage: Surgery is as above with either primary anastomosis and proximal diverting loop ileostomy or Hartmann's procedure (end colostomy). The second stage is the reversal of ostomy. In rare instances (not typically done) the Hartmann's is reversed and also protected with a diverting ileostomy, this will require a third stage operation to reverse the ileostomy.

All patients will require a bladder Foley catheter for a period of 7-10 days postoperatively [16].(B2)

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.

Differential Diagnosis

Few other processes present with pneumaturia. These include:

• Recent instrumentation of bladder can be determined with a detailed history
• Urinary tract infection (UTI) with a gas forming organism (emphysematous cystitis): Increased risk in people with diabetes and patients with urinary tract outflow obstruction. One will see air within the bladder wall on imaging. Treatment is primarily with antibiotics tailored to urinary cultures.

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.

Prognosis

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 [17].

• Complicated diverticular disease (abscess, fistula formation, strictures, and free perforation) is associated with a higher risk of colonic malignancy. There is about a 3% to 5% incidence of concomitant malignancy in patients who have uncomplicated diverticulitis and about an 11% incidence of harboring a malignancy for complicated diverticulitis.
• Patients who have the symptomatic diverticular disease should be evaluated with colonoscopy after acute infection subsides. This is especially true for complicated diverticular cases.
• Clinicians used to be taught that patients who suffer attacks of uncomplicated diverticulitis would subsequently have an increased chance of recurrence and increased chance of complicated disease with each subsequent attack. This has been proven false. Recent analyses of data have shown that patients are more likely to have complicated diverticulitis with their first attack and with each recurrent attack risk of complicated diverticulitis decreases.
• Elective colon resection is indicated for complicated diverticulitis as they have a high recurrence rate of up to 40%. Other indications for elective sigmoidectomy are more controversial.

Complications

Complications after elective colon resection for colovesicular fistula [8]:

• Mortality: 1% to 2.3%
• Morbidity: 6.4 % to 49% with a median of 19%
• Recurrence: 2.6% to 12.5%