Enterovesical Fistula

Etiology

An enterovesical fistula is a complication of an underlying disease or injury. A good understanding of the pathophysiology of the fistula formation process is essential for appropriate management and prevention. Several causes may result in this complication. Depending on the cause, the processing of developing the fistulae may range between months to years. Generally, any pathology of the wall of the bowel or bladder can lead to the development of a fistula. Other categories of causes include injury, including iatrogenic and radiation.

The common causes of enterovesical fistula are[5]:

1. Diverticular disease is by far the most common cause of enterovesical fistula. It accounts for two-thirds or more of this type of fistulae. Diverticular disease is much more common in large bowel than small bowel. Complicated diverticulitis is more likely to cause fistula than non-inflamed diverticula. Erosion of the diverticular wall with the components of inflammation and a small abscess can extend and involve the adjacent bladder wall to create the fistulous connection. An occasional increase in the luminal pressure in either side of the fistula and the continued inflammatory process will likely maintain the fistula patent.
2. Malignancy is the second common cause of enterovesical fistula[6]. It accounts for about 10% to 20% of the cases. Intestinal mucosal malignancy usually spread radially as well as circumferentially. Radial extension and destruction of normal tissue may extend to the nearby bladder wall creating the abnormal connection. Bladder malignancy can similarly cause the same fistula.
3. Crohn and other inflammatory diseases
4. Radiation[7]: Fistula manifests after a long lag period that could extend to years. A less common cause but within the same group of patients is chemotherapy.
5. Injuries: Either iatrogenic injuries like in pelvic surgeries or other injuries like in traumas of the pelvis are rare causes. [8]
6. Foreign bodies are a rare cause of fistula.[9]

The occasional mistake of considering the causes of non-healing of fistula abbreviated with the mnemonic FRIENDS as causes of fistula. It is correct that most causes included in FRIENDS are known causes of fistula formation, but they include unrelated factors like epithelialization or distal obstruction. A fistula that is already formed is unlikely to heal if the tract lining epithelializes, or the distal stream of the GI tract is obstructed. However, these factors by themselves are not known to cause fistula formation.

Epidemiology

Colovesical fistulae are the most common type of fistulous communication between the bowel and the urinary bladder. The incidence in patients with diverticular disease approximately 2%. Less than 1% of carcinomas of the colon result in fistula formation.

Colovesical fistulae are more common in males. A lower incidence in females is most likely due to the interposition of the uterus and adnexa between the bladder and the colon. In women, other types of fistulae are more common than colovesical fistulae. Women who present with colovesical fistulae are usually older or have a history of hysterectomy. Uterine atrophy or absence of the uterus may be predisposing factors.

Pathophysiology

An enterovesical fistula usually refers to a predisposing pathophysiologic process. Therefore, pathophysiology depends on the predisposing cause of disease. This extends from acute infectious process like in diverticulitis to the worst process as in malignancy. Consequent to the development of a fistula, an additional pathophysiologic process starts as a result of the connection between two different lumens. The most affected lumen is the bladder because it is sterile. Contamination of the bladder lumen with intestinal content, especially the colonic content with high bacterial load, results in persistent infection (cystitis).

Histopathology

Histopathologic examination of the tissue involved in the fistula reflects an acute inflammatory reaction besides the original pathology of the causative disease except in injuries. The acute inflammation is caused by a combination of more than one factor, like the primary pathology causing the fistula (diverticular disease, malignancy, Crohn, among others), tissue irritation by the flow of intestinal content, and the resulting infection. Other histopathological findings like chronic inflammation from radiation or Crohn, malignancy, and or injury-related necrotic process can be identified depending on the cause of the fistula. Identifying the fistula histopathology is usually a late stage after surgical treatment and excision of the fistula and related tissue. Occasionally intraoperative diagnosis is made by biopsying incidentally identified fistulae. Frozen section is used to determine the cause of fistula and plan the surgical treatment. The malignant fistulous tissue is treated surgically differently (usually with radical excision) than non-malignant tissue.

History and Physical

Like in almost all surgical diseases, signs and symptoms will involve the cause of the disease, the disease, and its complications. Occasionally fistula is the presenting finding of the underlying disease.[10] The most common signs and symptoms are recurrent urinary tract infection and pneumaturia.[11] Other signs and symptoms that can be identified in the history may include:

Signs and Symptoms of the Cause of the Disease

• Diverticular disease: Pain and other signs and symptoms of the infectious GI malignancy; general signs and symptoms of weight loss, weakness, cachexia, poor appetite; and local signs and symptoms of intestinal obstruction, GI bleeding, change of bowel habit, and abdominal pain with possible tenderness
• Inflammatory process: Lower abdominal pain/tenderness, fever, GI bleed, and alteration of bowel habit

History of known diseases causing enterovesical fistula should raise suspicion of the problem.

Signs and Symptoms of the Disease (Fistula)

Pneumaturia is a highly diagnostic symptom of enterovesical fistula.[11] On rare occasions, fecaluria (presence of fecal material in the urine) is present.[12]

Signs and Symptoms of the Complication

Recurrent or persistent urinary tract infection (UTI) is the most common complication of enterovesical fistula. 

Evaluation

Evaluation of enterovesical fistulas includes assessment to:

1. Confirm the diagnosis
2. Characterize further the site, size, and complexity of the fistula 
3. Identify the underlying pathology if it is unknown
4. Plan for management
5. Reevaluate and follow up progression

Several investigation modalities are available to achieve all or some of the above goals. The appropriate clinical practice is to start with simple tests, then base the rest of the investigation on the need. Confirming the diagnosis is not difficult. It is usually done with imaging.

Evaluation Modalities

In addition to the clinical evaluation that includes a comprehensive history and appropriate physical exam, the following modalities are available to evaluate enterovesical fistulas.

Imaging

Imaging with GI contrast that traverses through the fistula to the bladder provides satisfactory confirmation. On occasions, the contrast is not seen in the fistula itself but is seen in the end organ (bladder).

Small bowel follows through, or contrast enema can provide this confirmation.

CT provides more details about the tissue in the area and the fistula itself. It is helpful in planning for surgical treatment.

MRI may be needed in subtle or difficult to diagnose fistulae. It has the advantage of better soft tissue characterization. It is also useful in complex fistulas like in complicated Crohn.[13]

Endoscopy

Cystoscopy, or colonoscopy in the case of colovesical fistula, is useful to identify the site of the fistula at the mucosal of the scoped organ. A small area of inflamed, red, and possibly elevated mucosa is a sign of a possible fistulous tract. Unless the fistula is very wide, it is usually difficult to visualize its lumen endoscopically.

Endoscopy can provide further information about the underlying disease, like in malignancy or Crohn. Fistulas might an incidental finding of endoscopy performed for other reasons. In this situation, further investigations are required.

Treatment / Management

Treatment of enterovesical fistula includes treatment of the fistula itself and the underlying disease if it is treatable. Therefore, confirming the fistula etiology should be done before planning treatment. Good clinical practice is to treat with the least aggressive treatment modality with the best success rate.

Conservative or Non-operative Approach

Medical treatment of the symptoms and possible complications like UTI can be used in selected patients. This approach can be considered in high-risk patients and severe underlying disease. The associated complication rate from this approach is found to be low in recent studies.[14][15](B2)

Medical treatment includes treating UTI and the associated symptoms, maximizing medical treatment of the underlying disease like in Crohn's or diverticulitis, and support of the general patient's condition.

Other conservative treatment includes non-operative measures to close the fistula like fibrin glue or other occlusive measures. The success rate of these measures is not high. They are still an option to consider in high-risk patients.

Operative Approach

The basic principle of the surgical approach is to excise the involved segment of the bowel and the fistula[16][17]. After the diagnosis of the fistula and the underlying disease is confirmed and further characterized, surgical treatment can be planned accordingly. Limited conservative excision of the involved intestinal segment and the fistula is recommended in operative cases of the diverticular disease, limited Crohn, and other reversible inflammatory diseases[18][19]. Fistula site on the bladder wall can be over swan with an absorbable suture. The indwelling urinary catheter should be maintained for a few weeks during the healing process. More radical excision is recommended in operable malignancy. Oncologic excision of the intestine with partial cystectomy that includes the fistula site to a free margin is necessary[20]. Primary closure of the bladder wall is sufficient unless the trigon is involved.(A1)

An enterovesical fistula may sometimes be identified intraoperatively while operating on the underlying disease. Dense adhesions of the intestine on the bladder are the trigger to suspect the fistula. Unless it is cancer surgery, the operative approach is usually the same. If the pathology cannot be confirmed, a frozen section of the fistula tissue is needed to rule out malignancy.

Differential Diagnosis

• Aortitis

• Appendicitis

• Blunt abdominal trauma

• Colon cancer

• Diverticulitis

• Enterovesical fistula

• Inflammatory bowel disease

• Malabsorption

• Peptic ulcer disease

• Penetrating abdominal trauma

• Small intestinal diverticulosis

• Urinary tract infection