Fecal fistula refers to an abnormal passage between the intestinal tract and the genital tract, with the most common type being a rectovaginal fistula. Based on the location of the fistula within the vagina, it can be classified as low, medium, or high.
Etiology
Obstetric Trauma
Prolonged retention of the fetal head in the vaginal canal may compress and cause necrosis of the rectum, leading to a fecal fistula. Difficult or rough delivery procedures and surgical injuries, such as fourth-degree perineal tears, may also result in a fistula. This occurs when the rectum fails to heal after repair or when sutures in a perineal tear inadvertently penetrate the rectal mucosa without detection.
Pelvic Surgical Injuries
Procedures such as a hysterectomy or surgery involving the separation of severe pelvic adhesions may damage the rectum. In such cases, the fistula is typically located near the vaginal vault.
Inflammatory Bowel Diseases
Conditions such as Crohn’s disease or ulcerative colitis are other significant causes of rectovaginal fistulas. While inflammatory bowel diseases primarily affect the small intestine, the colon and rectum can also be involved.
Congenital Malformations
Congenital abnormalities may lead to non-traumatic rectovaginal fistulas. Additionally, surgeries to correct congenital abnormalities of the genital tract may result in secondary rectovaginal fistulas.
Other Causes
Prolonged placement of pessaries, advanced malignant infiltration of the genital tract, or radiation therapy in late-stage cancer can also lead to the development of fecal fistulas.
Clinical Manifestations
The primary symptom of fecal fistulas is the passage of feces through the vagina. Large fistulas may allow formed stool to pass through the vagina, while liquid stool may cause continuous leakage. In cases of small fistulas, vaginal contamination with fecal matter may not be observed, but intestinal gas may pass through the fistula and exit via the vagina, and liquid stool may leak in certain circumstances.
Diagnosis
Diagnosis is typically straightforward based on medical history, symptoms, and gynecological examination. Large fistulas are usually readily visible during a vaginal examination, while smaller fistulas can appear as areas of fresh granulation tissue on the posterior vaginal wall where the fistula is located. Digital rectal examination can detect the fistula by palpating its opening. For very small fistulas, a probe can be used to explore the granulation tissue in the vagina toward the rectum, and the probe will be palpable through the rectal wall.
Smaller fistulas located at the vaginal apex, or fistulas involving the small intestine or colon, may require barium enema studies for confirmation. If necessary, lower gastrointestinal endoscopy can be used to aid in diagnosis. Once the diagnosis is confirmed, treatment should address the primary cause, whether through medical or surgical methods. When the underlying disease is controlled through medical treatment, spontaneous healing of the fistula may be possible.
Treatment
Surgical repair is the primary treatment modality for fecal fistulas. For surgical injuries, immediate intraoperative repair is often performed. Repairs can be carried out via transvaginal, transrectal, or transabdominal approaches, depending on the situation. The choice of surgical technique depends largely on the cause, location, size of the fistula, the presence of multiple fistulas, and the surgeon's experience and skill. The primary surgical method involves excising the fistula, mobilizing surrounding tissue, and performing multi-layered suturing.
For high, large rectovaginal fistulas complicated by urogenital fistulas, or when previous surgeries have failed with severe vaginal scarring, a temporary sigmoid colostomy may be performed first, followed by fistula repair at a later stage.
The timing of surgical intervention is critical. Congenital fecal fistulas are generally repaired after the onset of menstruation, around 15 years of age, to avoid causing vaginal stenosis due to early surgeries. For pressure necrosis-associated fistulas, repairs are often postponed for 3–6 months to allow adequate healing of surrounding tissues. Preoperative preparation involves rigorous bowel preparation and the use of oral intestinal antibiotics. Postoperatively, intravenous hyperalimentation and oral intestinal motility inhibitors are provided. Gradual transition from water intake to oral feeding typically occurs 5–7 days after surgery. Maintenance of perineal hygiene is important throughout.
Prevention
The principles for preventing fecal fistulas are similar to those for urinary fistulas. Careful perineal protection during delivery is crucial for preventing fourth-degree perineal tears. After repairing perineal tears, digital rectal examination is performed routinely to check for sutures penetrating the rectal mucosa. If such sutures are identified, they are removed, and the repair is performed again.