A fistula is an abnormal connection between two epithelial surfaces. There are some exceptions of this definition like when the surfaces are not epithelial as in the endothelial surfaces of vascular fistulae or in the connection of gastrointestinal (GI) mucosa to a wound where no epithelial surface is included. An enterovesical fistula is an abnormal communication between the intestine and the bladder. Does the name imply more than the 2 connected surfaces? The organ of origin of the fistula is usually stated first. Therefore, with enterovesical fistula, the fistula usually begins from the intestine and ends to the bladder. However, the fistulization process could begin from the bladder wall and end in the intestine or other luminal structures. Most of the known and clinically encountered fistulae originate from the bowel.
The term bowel is generally used to indicate small intestine. It is interchangeably used in the literature to refer to all intestinal (small and large) fistulas with the urinary bladder. More specific terms are also used, including jejunovesical, ileo vesical, colovesical, sigmoid vesical or rectovesical fistulae to indicate the specific part of the intestine involved in the fistulae. Since colovesical fistula is by far the most common fistula between the intestine and the bladder, most of the content of this article will apply on colovesical fistula unless it is otherwise indicated.
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:
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.
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.
An enterovesical fistula usually refers to a predisposing pathophysiologic process. Therefore, the pathophysiology depends on the predisposing cause or 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).
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's, among others), tissue irritation by the flow of intestinal content, and the resulting infection. Other histopathological findings like chronic inflammation from radiation or Crohn's, 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 intra-operative 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.
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. The most common signs and symptoms are recurrent UTI and pneumaturia. Other signs and symptoms that can be identified in the history may include:
Signs and Symptoms of the Cause of the Disease
History of known diseases causing enterovesical fistula should raise suspicion of the problem.
Sings and Symptoms of the Disease (Fistula)
Signs and Symptoms of the Complication
Recurrent or persistent urinary tract infection (UTI) is the most common complication of enterovesical fistula.
Evaluation of enterovesical fistulas includes assessment to:
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.
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 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's.
Cystoscopy, or colonoscopy in case of colovesical fistula, are 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 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's. Fistulas might an incidental finding of endoscopy performed for other reasons. In this situation, further investigations are required.
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.
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.
The basic principle of the surgical approach is to excise the involved segment of the bowel and the fistula. 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's and other reversible inflammatory diseases. 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. Primary closure of the bladder wall is sufficient unless the trigon is involved.
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.
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