Urinary fistula refers to an abnormal passage formed between the genital tract and the urinary tract, resulting in the uncontrollable discharge of urine through the vagina. Urinary fistulas can occur at any point between the genital tract and the urinary tract. Based on their anatomical location, they are classified as vesicovaginal fistula, urethrovaginal fistula, vesico-urethro-vaginal fistula, vesico-cervical fistula, vesico-cervical-vaginal fistula, ureterovaginal fistula, and vesico-uterine fistula.
Etiology
The most common urinary fistulas are vesicovaginal fistulas and ureterovaginal fistulas, usually caused by obstetric trauma or pelvic surgery. Urethrovaginal fistulas are often complications of urethral diverticula, anterior vaginal wall prolapse, or surgical treatment for stress urinary incontinence.
Obstetric Trauma
Obstetric trauma was historically the leading cause of urinary fistulas, although it is now rarely seen in developed countries. It remains prevalent in regions with limited medical resources.
There are two main mechanisms:
- Necrotic-Type Urinary Fistula: This type occurs due to cephalopelvic disproportion caused by a narrow pelvis, macrosomia (excessively large fetus), or abnormal fetal position. Prolonged labor, particularly during the second stage, leads to compression of the anterior vaginal wall, bladder, and urethra between the fetal head and the pubic symphysis, resulting in ischemic necrosis of localized tissue and the formation of a fistula.
- Traumatic-Type Urinary Fistula: This occurs as a direct result of instrumental deliveries, particularly vacuum or forceps-assisted births. Traumatic-type fistulas are more common than necrotic-type fistulas.
Gynecological Surgical Injury
Urinary fistulas may result from abdominal or vaginal gynecological surgeries due to injuries incurred during tissue dissection. Vesicovaginal and ureterovaginal fistulas may form when the bladder or ureters are wounded during attempts to separate adhesions. Overdissection of the distal ureter can also lead to ureterovaginal fistulas, primarily caused by reduced blood supply to the ureter, resulting in delayed ischemic necrosis.
Other Causes
Other causes of urinary fistulas include radiation therapy, bladder tuberculosis, advanced gynecological or urological malignancies, improper placement of pessaries, and local drug injections for treatment purposes.
Clinical Manifestations
Urine Leakage
The most common and characteristic symptom is painless, continuous vaginal fluid leakage after childbirth or pelvic surgery. Depending on the fistula's location, the leakage may present as continuous leakage, positional leakage, stress incontinence, or overflow leakage. For example:
- Patients with higher-positioned bladder fistulas may not experience leakage when upright but may have persistent leakage when lying down.
- Those with very small fistulas may only have leakage when the bladder is full.
- Patients with a unilateral ureterovaginal fistula may still have voluntary urination because urine from the unaffected ureter continues to enter the bladder.
The timing of leakage can also vary based on the underlying cause:
- Necrotic-type urinary fistulas typically occur 3–7 days postpartum or postoperatively.
- Fistulas caused by direct surgical injury result in immediate postoperative leakage.
- Fistulas due to thermal energy devices often occur 1–2 weeks postoperatively.
- Ureterovaginal fistulas following radical hysterectomies commonly present 10–21 days postoperatively.
- Leakage caused by radiation damage tends to occur late and is often accompanied by rectovaginal fistulas.
Vulvar Itching and Pain
Continuous stimulation from leakage can lead to local irritation, tissue inflammation and hyperplasia, and infections. Urine exposure may cause vulvar itching, burning pain, and dermatitis-like changes. If the lower ureter on one side is severed, resulting in vaginal leakage, urine may irritate the apex of one side of the vagina, triggering hyperplasia of the surrounding tissues. Gynecological examination may reveal localized thickening in such cases.
Urinary Tract Infection
Patients with concurrent urinary tract infections may present with symptoms such as urinary frequency, urgency, dysuria, and discomfort in the lower abdomen.
Diagnosis
A thorough medical history, surgical history, the timing of urine leakage, and its characteristics are essential to the diagnostic process. The nature of the leaked fluid as urine should first be confirmed. Biochemical testing can compare the electrolytes and creatinine levels in the leaked fluid with those in urine and blood. Electrolyte and creatinine levels in urine are typically several times higher than those in blood; if the levels in the leaked fluid are similar to those in urine, this suggests the presence of a urinary fistula.
Vaginal examination can reveal larger fistulas, while smaller fistulas may be diagnosed through palpation of scar tissue around the fistula edges. For patients with a history of pelvic surgery, if no fistula is detected but urine is observed leaking from one side of the vaginal fornix, a ureterovaginal fistula is likely. When visualization during examination is inadequate, placing the patient in a knee-chest position and retracting the posterior vaginal wall with a single-bladed retractor may expose fistulas located in the upper vagina or near the vaginal fornix. Additional diagnostic tests may aid in confirming the presence of a fistula.
Methylene Blue Test
Three cotton balls are placed sequentially at the vaginal apex, the middle third of the vagina, and the distal end of the vagina. The bladder is filled with 300 ml of diluted methylene blue solution. The cotton balls are removed one by one, and the location of blue staining on the cotton is used to estimate the location of the fistula. Leakage of blue-stained fluid from a small hole in the vaginal wall indicates a vesicovaginal fistula. Leakage from the cervical os suggests a vesicocervical fistula or vesico-uterine fistula. If the cotton is unstained or yellow-stained, a ureterovaginal fistula may be suspected. In cases where no staining is observed but a fistula is suspected clinically, the test can be repeated after the patient engages in 30 minutes of activity before rechecking the cotton.
Indigo Carmine Test
Intravenous injection of 5 ml of indigo carmine may reveal blue-stained fluid leaking from the vaginal apex within 5–10 minutes, indicating a ureterovaginal fistula.
Cystoscopy and Ureteroscopy
These procedures may provide insights into bladder capacity and mucosal condition, whether inflammation, stones, or diverticula are present, and the location, size, and number of fistulas, as well as their relationship to the bladder trigone. Placement of ureteral catheters or direct ureteroscopic examination may also help identify the site of ureteral obstruction.
Imaging Studies
Intravenous pyelography (IVP) involves injecting a contrast agent to dynamically observe the urinary system through X-rays. Visualization of the renal pelvis, ureters, and bladder can help evaluate kidney function and ureteral patency, aiding in the diagnosis of ureterovaginal and vesicovaginal fistulas. Retrograde ureteropyelography can supplement cases where IVP fails to detect ureterovaginal fistulas. CT urography (CTU) provides clear images of the renal pelvis, ureters, and bladder and has become a new, non-invasive method for diagnosing urinary fistulas.
Renal Scintigraphy
This study evaluates renal and ureteral function.
Treatment
Surgical repair is the primary treatment for urinary fistulas. Non-surgical treatment may be considered only within the first week postpartum or postoperatively for vesicovaginal fistulas and small ureteral fistulas. A Foley catheter can be placed in the bladder or a ureteral catheter inserted under cystoscopy for 4 weeks to 3 months, during which spontaneous healing may occur. However, prolonged catheter use can irritate the mucosa, cause pain, interfere with daily activities, and reduce quality of life. For vesicovaginal fistulas treated non-surgically, suprapubic cystostomy drainage is recommended to ensure bladder decompression. Before removing a long-term catheter, repeat diagnostic testing, such as the methylene blue test, is required to confirm whether the fistula has healed. During catheterization, regular assessments of the patient’s condition should be conducted. Nutritional support and adequate fluid intake are important to promote fistula healing. Management of vulvar dermatitis and urinary infections is also critical to improving quality of life. In postmenopausal women, estrogen therapy may promote vaginal epithelial proliferation and aid in wound healing. Non-surgical treatment has a 15%–20% chance of spontaneous closure for small fistulas just a few millimeters in diameter that occur shortly after surgery. However, for epithelialized fistulas, non-surgical treatments are generally ineffective.
Timing is crucial for surgical repair. Directly injured urinary fistulas should be repaired as early as possible. Fistulas caused by other factors require waiting 3 months to allow tissue edema to subside and local blood supply to return to normal. For fistulas failing initial repair, at least 3 months should elapse before attempting secondary surgery.
Repair of radiation-induced fistulas may require an even longer healing period; some experts recommend waiting 12 months before repair. For surgically induced fistulas, a delay of several weeks may be necessary to allow for resolution of inflammation, softening of scar tissue, and restoration of adequate blood supply. During this period, urinary antibacterial therapy and estrogen supplementation (for postmenopausal patients) can be beneficial.
For vesicovaginal and urethrovaginal fistulas, vaginal surgery is the first-line approach. For cases unsuitable for vaginal surgery or complex fistulas, abdominal or combined abdominal-vaginal surgical approaches may be considered.
Treatment of ureterovaginal fistulas depends on their location and size. Small fistulas may heal spontaneously after ureteral stent placement (e.g., double J stent), although this is not effective for radiation-induced fistulas. If the fistula is near the ureterovesical junction, ureteral reimplantation into the bladder may be performed. For fistulas located farther from the bladder, excision of the segment containing the fistula and subsequent ureteroureterostomy can be performed. Stents are usually left in place for 3 months postoperatively.
Prevention
The majority of urinary fistulas are preventable. Improving obstetric care quality is crucial to addressing obstetric-related fistulas. For suspected injuries, catheterization may help ensure a decompressed bladder, supporting recovery of blood supply to compressed areas and preventing fistula formation. During gynecological surgeries, preoperative placement of ureteral catheters is advisable for cases anticipated to involve surgical difficulties, such as extensive pelvic adhesions or malignancies with widespread invasion, to make ureteral identification easier. Even during seemingly straightforward procedures such as total hysterectomies, a clear understanding of anatomical relationships is necessary before proceeding. Any intraoperative injuries to the ureter or bladder must be promptly repaired. Pessaries require regular removal, and proper placement and fixation of vaginal radioactive sources should be ensured during cervical cancer radiotherapy, with care taken not to exceed radiation dose limits.