Etiology

Common causes of rectovaginal fistulas include obstetric trauma, inflammatory bowel disease (IBD), radiation, sepsis, iatrogenic injury from anal or vaginal surgery, forceful coitus or impalement, carcinoma, or congenital abnormalities. Etiology is important to the pathophysiology and the ultimate response to surgical therapy. Frequently associated or underlying conditions must be addressed either preoperatively or at the time of surgery to facilitate successful outcome.

Obstetric trauma is the most common cause of rectovaginal fistulas. Labor and delivery result in rectovaginal fistulas in a number of ways. Prolonged labor with pressure necrosis of the rectovaginal septum is an uncommon but possible event that results in a mid-vaginal fistula and occurs more often in underdeveloped countries. More frequently, fistulas occur low in the vaginal fourchette after either an episiotomy or a third/fourth degree laceration that goes unrecognized, is inadequately repaired, or develops an infection with subsequent failure of repair. Fortunately, rectovaginal fistulas after vaginal delivery are uncommon, occurring in less than 0.1% of cases.2 Most of these injuries are associated with trauma to the sphincter mechanism. Recognition of a concomitant sphincter defect becomes an important part of the surgical approach and requires an appropriate anorectal physiologic evaluation before intervention. Trauma that is not obstetric related and can result in rectovaginal fistulas include forceful coitus, impalement, introduction of foreign body, and violence.

Rectovaginal fistulas can occur in both ulcerative colitis and Crohn's disease, although they tend to occur in the latter more frequently. In Crohn's disease, rectovaginal fistulas are included in the spectra of perianal disease and may precede the development of intestinal symptoms. In addition, recurrent rectovaginal fistulas and fistulas that develop in patients with a previous diagnosis of ulcerative colitis should raise the suspicion of the possibility of Crohn's disease. These patients should undergo an appropriate evaluation, including inquiry into intestinal symptomatology and imaging that may include radiologic assessment or endoscopic procedures.

A variety of vaginal or anorectal surgeries can lead to the development of rectovaginal fistulas including hysterectomy, especially if associated with dense pelvic adhesions; posterior colporrhaphy; transanal resections of anterior tumors such as villous adenomas or leiomyomas; fulguration of anterior lesions such as condyloma or recurrent adenocarcinoma not amenable to re-resection; sphincter repairs; low anterior resections in which the vaginal wall is partially incorporated in the anastomosis; or after leaks from low anastomoses involving colonic or ileal pouches.

Any perineal infection can lead to the formation of a rec-tovaginal fistula. Perirectal abscesses, venereal diseases, or Bartholin's cysts may induce inflammation leading to low rectovaginal fistulas. High fistulas are most often caused by diverticulitis, although tuberculosis and lymphogranu-loma venereum have been reported.

Cancer of the anus, rectum, vagina, cervix, or uterus can give rise to rectovaginal fistulas. Leukemia, aplastic anemia, agranulocytosis, and endometriosis have also been implicated. Approach to these types of fistulas is dependent on the extent and stage of the disease. Malignant fistulas carry a poor prognosis. When surgical removal is not practical, they are treated palliatively with fecal diversion or endoluminal stenting. Therapy for

Figure 13-2.2. Classification of rectovaginal fistulas based on location. (Reprinted with the permission of The Cleveland Clinic Foundation.)

Figure 13-2.1. Rectovaginal fistula.

these types of fistulas is secondary to that of the cancer treatment.

Pelvic radiation after gynecologic and anorectal malignancies leads to fistulas that are particularly difficult to manage especially if accompanied by diabetes mellitus and hypertension. Radiation causes small vessel obliteration and scarring in localized tissues that subsequently exhibit poor wound-healing capability. Irradiation of the rectovaginal septum may lead to ulceration and eventual breakdown, with fistula formation, of this thin wall. Because of the inherent poor vascularity in the surrounding irradiated tissue, these types of fistulas are not amenable to simple local repairs and often require delayed intervention and fecal diversion for successful repairs. High doses of radiation predispose to fistula formation. Consideration must be made at the time of fistula evaluation, of the possibility of cancer recurrence with procurement of appropriate biopsies.

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