Rectovaginal Fistula

Etiology

RVF formation results as a complication of an underlying disease, injury, or surgical event.[1][2] Diseases of the vagina or the pelvic organs can be complicated with a persistent connection between the rectum and vagina. The common causes of rectovaginal fistula are[3]:

Obstetric-related injury: This is the most common etiology of traumatic RVF, and probably for all RVFs.[4] This includes third- and fourth-degree lacerations during vaginal delivery.

Surgical procedure: Surgical interventions that cause unrecognized vaginal or rectal injury, insufficient tissue thickness between the two organs, or ischemia of the tissue may result in perforation and fistula formation through the damaged tissue.

Diverticular disease: Complex diverticular disease is a common cause of fistula connecting to an intra-abdominal organ like the bladder and vagina.[5] Erosion of the diverticular wall with inflammation and abscess can extend, involve, and erode the adjacent organ walls resulting in a fistulous connection. An occasional increase in the luminal pressure on either side of the fistula and the continued inflammatory process will maintain the fistula patent.

Crohn's disease: Chronic inflammatory bowel diseases, especially Crohn's disease, is a well-known cause of intestinal fistulization.[6] Crohn’s is a transmural disease that involves the entire thickness of the bowl, making an extension to and involvement of adjacent tissues and organs very common.

Malignancy: Cancer of the intestine or adjacent organs is a known cause of bowel perforation and fistulization. RVF can result from vaginal, cervical, or, more commonly, rectal cancer that involves the entire wall thickness and extends to the adjacent vagina. These fistulae are also called malignant fistulae.

Radiation[7]: Radiation causes long-term chronic tissue inflammation with poor healing and repair processes. Therefore, fistulae caused by radiation manifest after a lag period from radiation exposure.

Non-surgical injuries and foreign bodies: Injuries in trauma or a foreign body can result in a non-healing abnormal connection with the vagina.

There are several causes that are abbreviated in the mnemonic "FRIEND" (Foreign body, Radiation, Inflammation, Epithelization, Neoplasm, Distal obstruction). These are known causes of non-healing in fistulous diseases. They should not be mixed with the primary or underlying causes of fistula formation.

Epidemiology

The frequency of rectovaginal fistula varies according to the cause. They are typically classified by etiology, location, and size, which affects the treatment and prognosis.

Rectovaginal fistulas are divided into 2 groups by location:

• Low RVFs are located in the lower third of the rectum and the lower half of the vagina. They are closest to the anus and are repaired with a perineal surgical approach.
• High RVFs are located between the middle third of the rectum and the posterior vaginal fornix. They require a transabdominal surgical repair approach.
• Most RVFs are less than 2 cm in diameter and are stratified by size:
  • Small: Less than 0.5 cm in diameter
  • Medium-sized: 0.5 to 2.5 cm in diameter
  • Large RVFs: Exceed 2.5 cm in diameter

Pathophysiology

Like other fistulae, RVF is a result of a complication of an underlying disease, surgical procedure, or injury. A good understanding of the pathophysiological process helps to assess better, manage, and prevent fistulae. Loss of wall integrity with ongoing inflammatory, infectious, or neoplastic processes at the rectal or vaginal wall can lead to erosion to the adjacent tissue or organ and establish an abnormal fistulous connection. When the initial process is reversible or curable, such as diverticulitis, fistulae have a better chance to resolve.

Histopathology

Histopathologic examination of the tissue involved in the fistula reflects an acute inflammatory reaction besides the original pathology of the causative disease. 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, Crohn's disease, malignancy, and or injury-related necrotic process can be identified depending on the cause of the fistula.

History and Physical

The clinical presentation of RVF is a result of a combination of the passage of rectal content to the vagina and the underlying disease or injury. A detailed history of the underlying disease should be explored. Clinically, the escape of stool or gas from the rectum to the vagina through the fistula gives the abnormal signs and symptoms of foul-smell vaginal discharge, dyspareunia, passing air, bleeding, and passage of frank stool, especially when the patient has diarrhea. Further symptoms of complications like symptoms of cystitis or vaginitis are occasionally encountered. Symptoms of an underlying disease like rectal obstructing cancer or diverticulosis may be present.

Physical exam of the vagina, the source of the symptoms, will likely reveal irritation, erythema, swelling, discharge, stool, and possible fistula opening in the speculum exam. An office colposcopic exam may reveal more details of the vaginal epithelium and the fistula site as an indurated indentation. A rectovaginal examination may reveal signs of the underlying disease like an obstructing low rectal tumor or phlegmon, Crohn disease, or tissue atrophy from radiation.

Evaluation

When RVF is suspected, a workup should be started to confirm the diagnosis, assess the extent of the fistula, and identify the underlying diagnosis. In addition to history and physical examination, workup should be complemented by imaging and endoscopy if needed.

Laboratory tests to assess the baseline hematocrit, biochemical and infectious parameters are usually obtained. Signs of the overall disease impact, complications, and severity can be estimated from these tests. Further tests may be needed according to the initial assessment.

Endoscopy, like colposcopy and/or proctosigmoidoscopy (rigid or preferably flexible), may reveal the site of the fistula with the underlying disease. Signs of the underlying diseases like Crohn’s, diverticular disease, or rectal cancer are likely to be identified with endoscopy. Colposcopy can help detect cervical or vaginal cancers.

Imaging is commonly used and useful to confirm the diagnosis and identify the underlying disease. CT scan provides accurate, objective, detailed information of the fistula, the underlying disease, and the related nearby area. Rectal and intravenous contrast will outline the fistulous tract and the related structures. The presence of rectal contrast in the vagina is a confirmation of the diagnosis even if the fistulous tract itself cannot be visualized.

Further assessment includes laboratory workup to evaluate the general patient condition, underlying disease, or complications of the fistula like infection or electrolyte imbalance. Tissue biopsy from suspected masses will help to confirm malignancy and its origin.

Treatment / Management

Treating RVF involves treating the underlying disease, the fistula itself, and any related complications.[8][9] Therefore, confirming the fistula etiology should be done before planning treatment. The treatment approach depends on condition severity, acuity, presenting symptoms, patient's general condition, underlying etiology, and complications resulting from the fistula.[10](B2)

Treatment of Crohn's disease, diverticular disease, or colorectal or gynecologic cancers should follow the principles of treating these diseases primarily. Treating RVF depends to a great extent on treating the underlying primary disease. There is more than one approach to the treatment of fistula with curative intent. In 2016, the American Society of Colon and Rectal Surgeons reviewed the approaches and developed guidelines to manage RVF.

Medical Treatment

The Conservative or non-surgical treatment approach of the symptoms and possible complications like UTI, local irritation, and site infection can be used in selected patients. This approach can be considered in high-risk patients and severe underlying disease. Medical treatment includes treating the infection and the associated symptoms, maximizing medical treatment of the underlying disease like in Crohn disease or diverticulitis, and supporting 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 who are not fit for surgery or failed a prior surgical approach.

Surgical Approach

Multiple operative approaches are used to treat RVF depending on complexity, recurrence, and the underlying disease.[11][12][13][14] Simple measures like draining seton in recurrent or acute infection may be used to optimize local tissue integrity and treat the infection.(B2)

The proximity of the rectal wall to the vaginal wall with minimal tissue makes repairs connecting fistula challenging. The principles of successful repair are to remove the unhealthy fistula tissue, replace with healthy tissue that has a good blood supply to enhance healing, and maintain thick interposing tissue between the rectal and vaginal walls. Following these principles (although not always possible) increase the chance of successful fistula treatment.

Fistula debridement and flaps are common surgical approaches. Advancement local endo-rectal flaps in simple RVF or gracilis regional myocutaneous flap in more complicated RVF are of the common flaps.[12][15]

In proximal or high RVF, surgical excision of the rectal wall in regimental resection is the other surgical radical approach.

Differential Diagnosis

• Aortitis

• Appendicitis

• Blunt abdominal trauma

• Colon cancer

• Diverticulitis

• Enterovesical fistula 

• inflammatory bowel disease 

• Large bowel disease

• Malabsorption 

• Urinary tract infection and cystitis in females

Prognosis

Typically patients can return to their regular routine a week or two following surgery, but it will probably be several months for complete healing to occur. These factors depend on the fistula's size and how extensive the surgical intervention was.

Complications

Rectovaginal fistula complications include fecal incontinence, associated hygiene issues, vaginal, perineal, or anal irritation, potential life-threatening abscess, and fistula recurrence.[16]