Bladder fistula is an abnormal communication between the bladder and an adjacent organ or skin. The most common type is colovesical fistula (60-70%), typically developing as a complication of sigmoid colon diverticulitis. Other types include enterovesical (small bowel), vesicovaginal (most commonly from obstetric injury), vesicocutaneous, and vesicouterine fistulas. The classic triad of colovesical fistula is pneumaturia (air in urine), fecaluria (feces in urine), and recurrent polymicrobial UTI. Crohn's disease, pelvic malignancy (especially rectal and cervical cancer), pelvic surgery, and radiotherapy are other important causes. Imaging evaluates intravesical air (pneumocystis), the connection between the bladder and fistula tract, perivesical inflammation, and adjacent organ pathology. CT is the most sensitive imaging modality; detection of intravesical air has >90% sensitivity.
Age Range
30-80
Peak Age
60
Gender
Equal
Prevalence
Uncommon
The pathophysiology of bladder fistulas varies according to the underlying cause. In colovesical fistula, the most common mechanism is a complication of sigmoid colon diverticulitis: diverticulitis → pericolic abscess → abscess extends toward the bladder wall → penetrates the bladder wall → fistula tract forms. Diverticulitis-related colovesical fistula is more common in males because the uterus normally serves as a protective barrier between the bladder and sigmoid colon. In Crohn's disease, transmural inflammation can directly penetrate the bladder wall. In malignancy-related fistulas, tumor invasion directly infiltrates the bladder wall. Radiation fistulas occur as late complications from endarteritis obliterans and tissue ischemia (months to years after radiotherapy). On imaging, intravesical air reflects gas passage from the fistula tract to the bladder lumen — on CT, air is clearly separated from surrounding urine (0-20 HU) by its very low HU value (-1000). Perivesical inflammation and fat tissue changes indicate spread of the chronic inflammatory process to surrounding tissues.
Free air in the bladder lumen without catheterization history is the most sensitive and earliest detected finding of enterovesical fistula. Air accumulating at the highest point of the bladder on CT cannot be missed due to the ~1020 HU density difference with urine. Clinically correlates with pneumaturia (air passage in urine). After excluding emphysematous cystitis, recent instrumentation, or Fournier gangrene, it largely confirms the diagnosis of fistula.
Free air foci in the bladder lumen — clearly separated from urine on CT by very low density (-1000 HU). Air typically accumulates at the highest point of the bladder (along the anterior wall in supine position). Intravesical air is highly specific for fistula in the absence of bladder catheterization or recent instrumentation history. The amount of air can vary from a few small bubbles to a level filling the entire bladder lumen. Associated bladder wall thickening and perivesical inflammation should be investigated.
Report Sentence
Free air is observed in the bladder lumen, consistent with enterovesical or colovesical fistula in the absence of catheterization history.
Fistula tract observed as a soft tissue density band or tubular structure between the bladder wall and adjacent organ (sigmoid colon, small bowel, vagina). Air, fluid, or contrast material passage may be seen within the tract. In colovesical fistula, the tract usually extends from the bladder dome or posterosuperior wall to the sigmoid colon. Surrounding perivesical fat stranding and thickened fascial planes are present. Oral contrast use facilitates confirmation of fistula tract — presence of oral contrast in bladder lumen confirms the fistula.
Report Sentence
A fistula tract is observed between the posterosuperior bladder wall and the sigmoid colon with surrounding perivesical inflammatory changes; consistent with colovesical fistula.
On T2-weighted images, the fistula tract appears as a high signal (hyperintense) tubular or linear structure — fluid and inflammatory tissue within the tract produce bright signal on T2. Surrounding inflammatory tissue and edema also appear hyperintense on T2. MRI demonstrates soft tissue details of the fistula tract superiorly to CT and is particularly preferred for evaluation of vesicovaginal fistulas. Sagittal and coronal T2 images best evaluate tract extent.
Report Sentence
A hyperintense fistula tract between the bladder and adjacent organ is observed on T2-weighted images with surrounding inflammatory edema findings.
The fistula tract and surrounding inflammatory tissue may show diffusion restriction on DWI — especially in the presence of active infection or abscess. Purulent material within the tract shows prominent diffusion restriction due to high viscosity and cellular debris. ADC values are low. This finding is helpful in distinguishing active fistula from inactive or healed fistula.
Report Sentence
Diffusion restriction is observed in the fistula tract and surrounding area on DWI, consistent with active inflammatory/infectious process.
Prominent enhancement of the fistula tract wall on contrast-enhanced MRI — reflects increased vascularity of active inflammatory granulation tissue. Enhancement is also observed in perivesical and pericolic fat tissue surrounding the tract. The enhancing wall may form a 'ring enhancement' pattern surrounding low-signal fluid in the tract lumen. Fat-sat T1 post-contrast sequences best demonstrate tract wall enhancement.
Report Sentence
Prominent enhancement of the fistula tract wall is observed on contrast-enhanced images, consistent with active inflammatory process.
Mobile echogenic foci in the bladder lumen on ultrasonography — representing intravesical air bubbles. Air bubbles shift position when the patient changes position and may create 'dirty shadowing' artifact. Additionally, focal bladder wall thickening, perivesical fluid, and wall thickening or diverticula in the adjacent organ (sigmoid colon) may be seen. US sensitivity is lower than CT but useful for initial evaluation.
Report Sentence
Mobile echogenic foci in the bladder lumen are observed, consistent with intravesical air; CT is recommended for investigation of enterovesical fistula.
Presence of oral contrast in the bladder lumen confirms the fistula when oral contrast is administered. Barium sulfate or iodinated oral contrast passes from the digestive tract through the fistula tract to the bladder lumen. On delayed phase CT, material at oral contrast density in the bladder lumen shows significantly different density from surrounding urine. This finding provides definitive diagnosis of enterovesical or colovesical fistula.
Report Sentence
Presence of oral contrast material in the bladder lumen is observed, confirming the definitive diagnosis of enterovesical/colovesical fistula.
Criteria
Fistula between bladder and colon (usually sigmoid). Most common type (60-70%). Due to diverticulitis, colon cancer, or Crohn's disease.
Distinct Features
Tract extending from bladder dome or posterosuperior wall to sigmoid colon. Accompanied by perisigmoid inflammation and diverticulitis findings. Pneumaturia and fecaluria are pathognomonic. More common in males (uterine barrier effect).
Criteria
Fistula between bladder and vagina. Obstetric injury (prolonged labor, cesarean section) is the most common cause. Obstetric causes predominate in developing countries, surgical complications in developed countries.
Distinct Features
Continuous vaginal urine leakage is the main symptom. Sagittal T2 MRI images best demonstrate the tract between the bladder base and anterior vaginal wall. MRI is preferred over CT — superior soft tissue contrast.
Criteria
Fistula between bladder and small bowel. Crohn's disease is the most common cause. Ileovesical fistula is most common as ileum is the small bowel segment closest to the bladder.
Distinct Features
In the context of Crohn's disease, terminal ileum wall thickening, skip lesions, and mesenteric inflammation are accompanying. CT enteroclysis provides detailed evaluation of the tract.
Criteria
Fistula due to pelvic malignancy (rectum, sigmoid, cervix, bladder carcinoma) invasion. Forms through tumor infiltration.
Distinct Features
Irregularly marginated, enhancing mass tissue around the fistula tract. Regional lymphadenopathy may accompany. Fistula is more irregular and asymmetric than inflammatory types.
Distinguishing Feature
Emphysematous cystitis may contain air within the bladder wall and lumen but no fistula tract exists. Occurs in diabetic patients due to gas-producing bacteria. Intramural gas within the bladder wall differs from bladder fistula — in fistula, air freely accumulates in the lumen.
Distinguishing Feature
Extravesical invasion of urothelial carcinoma may be confused with fistula but carcinoma is dominated by focal asymmetric mass and enhancement. In fistula, focal wall thickening and perivesical inflammation are present but no mass. Pneumaturia and fecaluria are symptoms specific to fistula.
Distinguishing Feature
Bladder diverticulum extends outward from the bladder wall but has no connection to another organ. Diverticulum contains only urine; in fistula, air and/or fecal material may be present. Open connection exists between diverticular neck and bladder lumen but no tract to surrounding organ.
Distinguishing Feature
Urachal cyst is in midline location between bladder dome and umbilicus and has cystic structure; fistula tract shows solid connection. Infected urachal cyst may open to bladder lumen but has no connection to bowel and intravesical air is not expected.
Urgency
urgentManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralTreatment of bladder fistula depends on the underlying cause. For diverticulitis-related colovesical fistulas, surgery (single-stage sigmoid resection + fistula repair) is the standard treatment; successful in >90% of patients. For Crohn's disease-related fistulas, medical therapy (anti-TNF agents) may be attempted but surgery is frequently needed. For malignancy-related fistulas, staging takes priority — surgery for operable disease, palliative diversion or chemoradiotherapy for inoperable disease. For vesicovaginal fistulas, surgical repair (vaginal or abdominal approach) is performed. Bladder drainage (catheter) provides immediate palliation for symptom control.
Bladder fistula usually requires surgical repair in symptomatic patients. Vesicocolonic fistulas originate from diverticulitis (60-70%) or colorectal cancer (20-25%). Vesicovaginal fistulas most commonly result from hysterectomy complications. CT cystography and MRI are the gold standard for diagnosis. Biopsy may be needed to exclude malignancy. Treatment involves addressing the underlying cause and surgical fistula repair.