These are usually because of previous hysterectomy, Crohn’s disease, diverticular disease, cancer, or operation. The fistula is usually from the ileum, sigmoid, or anastomotic site with posterior fornix of the vagina.

These follow radiotherapy or pelvic operations of the rectum or uterus. The fistula is usually between the posterior fornix of the vagina with middle third of the rectum.

They may be secondary to obstetric cause, rectal neoplasia, or inflammatory bowel disease. The fistula is between the lower third of the rectum and midportion of the vagina.

These fistulas are seen secondary to obstetric injury, foreign bodies, and local trauma and pelvic repair surgery. The fistula lies at the level of anorectal ring.

These are usually associated with anal gland infection, perirectal abscess, Bartholin’s abscess, Crohn’s disease, or previous anal surgery or anal anastomosis. The transsphincteric variety is becoming more common after ileoanal and coloanal anastomosis (Keighley et al. 2008).

This may prove to be one of the most effective diagnostic tools in uncooperative patients and may even reveal better details in most of the patients and help to plan the most suited surgery. This will also allow you to take multiple biopsies to rule out an inflammatory bowel disease and malignancies.

It may provide some useful information in fistulas secondary to radiation or inflammatory bowel disease. These conditions will usually alter the resting anal pressure, squeeze pressure of sphincter, and compliance of the rectum to function as a reservoir.

Neurophysiologic testing with pudendal nerve terminal motor latency can be performed in selected instances, but it hardly has any prognostic significance, hence not performed in most of the centers (Saclarides 2002).

This contrast study is one of the time-tested investigations performed in many centers with a water-soluble contrast medium which has a sensitivity of 79–100 % (Arnold et al. 1990; Bird et al. 1993; Giordano et al. 1996).

This investigation can give general information about the health of the colon and rectum. This investigation, however, may fail to identify fistula in many patients, hence at present not practiced in most of the centers.

A CT scan of the abdomen and pelvis with oral contrast may help to pick up the phlegmon or a neoplastic mass and detect the position of the gut responsible for a fistula.

It is a very good investigative tool in patients who complain of incontinence along with complaints suggestive of an RVF (Figs. 7.4 and 7.5). Ultrasound can identify internal anal sphincter as a uniform hypoechoic circle under the submucosa. Defects can be easily picked up in the internal anal sphincter with the use of EUAS, but defects in the external sphincter are difficult to appreciate. The reason being that external sphincter fibers are hyperechoic, striated, and more loosely arranged in circular pattern.

The normal thickness of the perineal body as measured from anal mucosa to posterior vaginal wall is 12 mm, and obstetric injuries usually cause thinning of the muscle within perineal body and shortening of the height of the high-pressure zone of the anus. EAUS is a good investigation to pick up these changes (Saclarides 2002). However, some studies report that initial evaluation with EAUS is not satisfactory (Choen et al. 1991), but its diagnostic accuracy has improved with technical advances in ultrasonography including the use of hydrogen peroxide (H₂O₂) as a contrast agent and 3D reconstruction (Cheong et al. 1993; West et al. 2004). The image is no longer limited to axial phone in 3D-EAUS, but it is possible to cut across any part of the data in the coronal, sagittal, or oblique plane (Fig. 7.6a, b). The H₂O₂-enhanced 3D-EAUS is expected to diagnose anal fistula with high accuracy. Kim and Park (2009) concluded in their study on 3D-EAUS assessment of an anal fistula with and without H₂O₂ enhancement on 61 patients that 3D-EAUS is highly reliable in the preoperative evaluation of anal fistula. The use of H₂O₂ for enhancement offers some benefits, although it did not significantly improve the diagnostic accuracy in this study. The selective use of H₂O₂ may be economical and reliable in difficult cases.

The test creates images of soft tissues in a patient’s body. MRI can show the location of a fistula, as well as involvement of pelvic organs or the presence of a tumor (Fig. 7.7a, b). Comparative studies of endoluminal ultrasonography and endoluminal MR imaging have comparable positive predictive values in revealing the location of anovaginal and rectovaginal fistulas (Stroker et al. 2002).

Endoanal MRI provides high-resolution multiplanar images of the anal canal, the rectum, and the vagina. The T2-weighted sequences can depict lesions with high signal intensity such as fistulas and fluid collection. Studies have shown that endoanal MRI is an excellent modality for the assessment of simple as well as complicated anovaginal fistulas and allows evaluation of anovaginal fistulas and additional abnormalities such as abscesses within the rectovaginal septum secondary perianal fistula tracts and sphincter damage (Dwarkasing et al. 2004).

This is helpful in RVFs secondary to obstetric or operative trauma or fistulas complicated by secondary infection. Use local wound care, drainage of infectious material, and antibiotics till the infection settles. Allow tissues to heal for 6–12 weeks. Many fistulas may heal completely and require no further treatment. Fistulas which persist can be repaired at a later date when the tissue is supple and infection is completely controlled.

In patients with IBD, appropriate medical therapy should be started. Repair of RVF can be carried out even when the patient is on steroids but with the understanding that chances of recurrence are high. Some patients can maintain RVF repair while on antimetabolites like 6-mercaptopurine or azothioprine. Some fistulas heal completely on infliximab but most improve symptomatically. If the patient presents with significant colonic involvement and anal stricture, then a fecal diversion should accompany the fistula repair.

RVFs which do not settle with conservative management will finally need one or the other types of surgery for the long-term cure. It is important to know that RVFs originating from radiation therapy, IBD, and stapling procedures are quite difficult to treat surgically. A proper evaluation, an appropriate selection of surgical procedure, and an experienced hand to tackle with the problem would be worthwhile to save the patient from the misery of repeated surgeries. Broadly surgical approaches may be perineal or abdominal as described under.