A rectovaginal or anovaginal fistula is a communication between the rectum or anus and vagina. The most common cause is obstetric-related trauma from unsuccessful repair of third- or fourth-degree perineal laceration or pressure necrosis secondary to prolonged labor. Patients complain of passage of gas, feces, mucus, or blood through the vagina. In the setting of traumatic injuries, anal manometry and endoanal ultrasound may demonstrate the severity of the underlying sphincter defect and help guide the surgical approach.
Anatomy
The rectum descends in midline following the sacral concavity and widens laterally. It is covered anteriorly and on both sides by peritoneum. As it descends towards the pelvic floor the peritoneal covering is reflected forward off the rectum onto the base of bladder or uterine body – forming the Pouch of Douglas. It descends further before penetrating the pelvic floor/levator ani where it transitions to the anal canal. The anterior relation of the distal rectum is the rectovaginal septum.
The rectovaginal septum is the thin septum separating the anterior rectal wall and the posterior vaginal wall. The caudal portion of the septum is the perineal body. The anal sphincters are located in the posterior portion of the perineal body at the junction of rectum and anus. The transverse perineal muscle traverses the perineal body and is often used in anal sphincteroplasty and rectovaginal fistula repair.
The sphincter apparatus consists of the internal and external sphincters and can be considered as two tubular structures overlying each other.
The internal sphincter is a continuation of the circular muscle layer of the rectum which becomes thickened and round distally, terminating approximately 1.5 cm below the dentate line, just cephalad to the external sphincter (intersphincteric groove). Contraction is independent of voluntary central innervated by autonomic nervous system.
The external sphincter is elliptical and surrounds the internal sphincter superiorly and is continuous with the puborectalis and levator ani muscles. The perineal body is formed by the constitution of the external sphincter, bulbospongiosus, and transverse perineal muscles anteriorly. The paired levator ani muscles form the bulk of the pelvic floor, and their fibers decussate medially with the contralateral side to fuse with the perineal body around the prostate or vagina. The external sphincter is thicker posteriorly than it is anteriorly, particularly in females. It is innervated by inferior rectal branch of internal pudendal and perineal branch of fourth sacral nerve (S4).
Management
Rectovaginal fistulas can be managed operatively or non-operatively. Consider the underlying disease, size of the fistula, presence of active inflammation, and severity of symptoms. Small, low-output fistulas may close spontaneously and a non-operative approach can be undertaken. If there is underlying infection, administration of IVABx may provide a useful adjunct.
Operative management is required for larger or chronic fistulas, and is based on location of the fistula:
- High rectovaginal fistulas (upper third of the vagina): transabdominal approach
- Low rectovaginal fistulas: extraabdominal ie. transvaginal, transrectal, or transperineal approach
Transabdominal
This approach requires mobilization of the rectovaginal septum, division of the fistula, and subsequent closure of the rectal and vaginal defects. Placement of a viable pedicle of tissue between the two structures may help augment the repair and promote healing. In some cases, no rectal resection is necessary. In the setting of severe prior radiation exposure, inflammatory bowel disease, or neoplasia, rectal excision is required. A low anterior resection or coloanal anastomosis may be possible, preserving the sphincters and allowing normal evacuation.
Extraabdominal
An endorectal advancement flap, sphincteroplasty, and transperineal procedures can all be employed for the repair of a truly low-lying fistula/anovaginal fistula. An endorectal advancement flap consists of a flap of rectal mucosa, submucosa, and underlying internal anal sphincter muscle that is advanced to cover the primary opening in the rectum or anus. The flap is best suited for the initial repair or for patients without an underlying sphincter defect. The transperineal approach (perineoproctotomy) converts the rectovaginal fistula into a fourth-degree tear. The tissues are then reapproximated in a normal anatomic fashion with the internal, external, and levator muscles in discrete layers. This should be reserved for patients with preexisting sphincter defects for whom other more conservative approaches have failed.