Epidemiology
The proportion of rectovaginal fistulas among all anal fistulas is about 5% (85). They are particularly often due to birth trauma (88%) and occur after 0.1% of all vaginal deliveries (36). Other causes include chronic inflammatory bowel diseases (especially Crohn's disease) with up to 2.1% and low anterior rectal resections with up to 10% (85, 24, 43, 56, 57, 69). Rectovaginal fistulas are increasingly observed as complications after procedures for hemorrhoidal disease and functional pelvic floor disorders, especially when stapling devices or foreign materials are used (3, 27, 35, 49, 64).
Classification
A uniform classification of rectovaginal fistulas does not exist. There are classifications based on cause, size, and location. Another classification distinguishes between simple and complicated fistulas: complicated are classified as Crohn's fistulas and radiation-induced fistulas.
For surgical management, it is recommended to distinguish between high and low fistula forms: high fistulas require an abdominal approach, while low forms can be repaired via an anal, perineal, or vaginal approach. Since the assessment of a possible perineal defect also influences the surgical strategy, the classification by Fry et al. is mentioned here (26, 19, 40, 41, 52):
I Perineal defect without fistula
II Perineal defect with fistula in the lower third of the vagina
III No perineal defect, fistula in the lower third of the vagina
IV No perineal defect, fistula in the middle third of the vagina
V No perineal defect, fistula in the upper third of the vagina
Etiology
Rectovaginal fistulas mainly arise from trauma, with other causes being inflammatory processes and postoperative complications following procedures in the pelvis (12, 18, 72, 75, 85).
Postpartum rectovaginal fistulas
- 88% of all rectovaginal fistulas (75)
- Caused by: stretching trauma with tearing of the perineum and rectovaginal septum (29)
- 5% of all vaginal deliveries lead to a third- or fourth-degree perineal tear; risks: high birth weight, forceps deliveries especially in older mothers (4, 37)
- The primary, immediately postpartum repair of the perineal tear leads to good results in about 95% of affected women. (72)
- 1 – 2% of all higher-grade perineal tears (Grade IV: complete tearing of skin, perineum, anal sphincter, and rectal mucosa) result in a rectovaginal fistula due to dehiscence of the primary repair or inadequate care. (36)
- Rare: spontaneous healing of the fistula in the early postpartum phase (36, 68)
- Common in postpartum fistulas: simultaneous sphincter lesions with fecal incontinence (19, 40, 41, 52)
Rectovaginal fistulas due to local infections
- Primarily cryptoglandular infection and inflammation of the Bartholin's glands (33, 92)
- Rare: tuberculosis (72), lymphogranuloma venereum (47), amoebiasis (22), schistosomiasis (45), inflammatory changes/erosions due to foreign bodies such as retained intrauterine devices (2, 6, 10, 34, 38, 67, 70), misuse of suppositories containing ergotamine or nicorandil (59, 65, 73)
- Also: HIV and associated infections (1, 60, 74), Behçet's disease (13, 15)
Rectovaginal fistulas after rectal resection
- Caused by iatrogenic perforation of the vagina and the use of stapling devices
- In up to 10% of all low rectal anastomoses (43, 51), e.g., in malignancies, pouch formation in chronic inflammatory bowel diseases (23, 25), and in proctocolectomy due to polyposis coli (55)
- Another risk factor: pre- or postoperative radiochemotherapy; up to 6.5% fistula formation (16, 42, 46)
- Most important risk factor: use of stapling devices, e.g., accidental inclusion of the vaginal wall after previous hysterectomy (5, 39, 43, 56, 57, 69, 80, 89), but also anastomotic insufficiency, which initially unnoticed, leads to an abscess in the pelvis that then drains through the vagina (50, 76)
Rectovaginal fistulas after other surgical procedures on the rectum and in the pelvis
- Transanal tumor resections (rectal anterior wall), hemorrhoid operations using staplers, but also procedures for pelvic floor dysfunctions (prolapse, rectal prolapse, rectocele, incontinence) using staplers or mesh implantation
- Increased postoperative fistula formation after stapler hemorrhoidopexy, usually due to inclusion of the posterior vaginal wall (3, 8, 17, 30, 31, 32, 53, 63), after technically complex procedures like STARR ("stapled transanal rectal resection") or TRANSTAR ("transanal stapled resection") (7, 27, 58, 62, 63, 64, 78) as well as after mesh implantations in the treatment of pelvic floor disorders (14, 35)
Symptoms and Diagnosis
The diagnosis of a rectovaginal fistula is based on history and clinical examination (44): passage of air and mucus, possibly also stool through the vagina. Questions about previous surgeries and obstetric complications are essential as well as about the psychological burden on the affected women.
The vast majority of rectovaginal fistulas are located at the level of the dentate line and communicate with the posterior vaginal fornix. The fistula usually runs slightly curved at the upper edge of the sphincter. During clinical examination, the rectum and vagina must be inspected. Before surgical measures and especially in unclear findings, further diagnostics are required: colonoscopy, CT, MRI. The detection of sphincter lesions can be very well performed by endosonography with appropriate experience and should complement the rectal-digital examination and manometry (77, 79).
Therapeutic Procedures
Sufficient treatment of rectovaginal fistulas always requires surgical intervention, but it poses a surgical challenge. The approach largely corresponds to that for high transsphincteric anal fistulas.
Decisive influence on the choice of therapy is exerted by local conditions such as location, fistula size, and tissue conditions such as inflammation and sphincter lesions (71). The most common procedure is fistula excision with sphincter suture and closure of the rectal defect by a sliding flap.
Pinto et al. compiled an overview of the various procedures in 2010 (66). The initial success ("fistula healing") is only 60% in almost all procedures on the first attempt and shows significant differences regarding fistula etiology. Rectovaginal fistulas that occurred postpartum or as a result of surgery could be healed in up to 70% of cases, Crohn's fistulas only in 44% of cases. Repeat interventions are therefore not uncommon for definitive fistula healing.
Endorectal Closure
The endorectal closure of rectovaginal fistulas consists of a transanal fistula excision with sphincter suture and subsequent coverage of the suture by a sliding flap ("flap") from mucosa-submucosa or full-thickness rectal wall, in isolated cases also by an anoderm sliding flap. The procedure was described by Belt in 1969 (9) and corresponds to the principle of the flap technique in high anal fistulas (61). The success rates of the procedure range between 50 and 70%.
Transperineal Closure
In the transperineal procedure, access is gained via the rectovaginal space. After separating the rectum from the vagina, the separate defect repair of the rectal anterior wall and posterior vaginal wall is performed, and then the rectovaginal septum is augmented by adapting the levator muscles. In the same session, a necessary sphincteroplasty can be performed (54, 71, 84), which is the most significant aspect of the procedure.
The disadvantage is the relatively large perineal wound associated with the risk of wound healing disorders. The healing rates are good at around 80% (21, 82), which is why the guidelines also recommend the transperineal procedure for fistula closure and simultaneous sphincter reconstruction.
Wound Control and Perioperative Complications
Immediate complications include bleeding and urinary retention, with these complications being much more common after hemorrhoidal procedures. Causes of postoperative urinary retention include insufficient pain management and excessive intravenous fluid administration (83, 90). There is a risk of local infections with secondary dehiscence of sutures, so adequate drainage of deeper wound parts should be ensured. Postoperatively, stool should be kept soft, e.g., by taking a mild laxative.
Relevant postoperative complications include dyspareunia due to narrowing of the vagina or scar formation (86), affecting about 25% of sexually active patients (21, 91).
Stoma Formation
In the context of anal fistula surgery, stoma formation is rather rare, but it is much more common in rectovaginal fistulas. The surgical approach to rectovaginal fistulas itself does not constitute a mandatory indication for stoma formation; rather, it should be based on findings. Primarily affected are patients with significant destruction of the anal canal and resulting fecal incontinence. In fistulas after rectal anastomoses and in Crohn's fistulas, the indication should be more generously made (11, 20, 28, 48, 81, 87, 88).