Chest CT with IV Contrast for Enterovesical Fistula
No, a chest CT with IV contrast is not indicated for evaluation of suspected enterovesical fistula—the appropriate imaging is CT abdomen and pelvis with IV contrast, ideally with oral or rectal contrast and delayed imaging. 1
Correct Imaging Protocol for Enterovesical Fistula
CT abdomen and pelvis with IV contrast is the primary imaging modality for suspected enterovesical fistula, with the addition of oral or rectal contrast and delayed scanning significantly improving detection of the fistulous tract. 1
Key Technical Requirements
- IV contrast administration is essential to visualize and characterize fluid collections, abscesses, and fistulous tracts 1
- Oral or rectal contrast with delayed scanning is specifically useful to detect enterovesical fistulas and infected fistulous tracts 1
- Water-soluble contrast should be used (not barium) when fistula is suspected 1
Diagnostic Performance
CT demonstrates high sensitivity for enterovesical fistula detection, with characteristic findings including:
- Intravesical air (90% of cases) is the most common CT finding 2
- Focal bladder wall thickening (90%) at the site of fistula communication 2
- Thickening of adjacent bowel wall (85%) indicating the primary disease process 2
- Extraluminal mass often containing air (75%) representing the underlying pathology 2
- Direct passage of oral/rectal contrast into bladder (20%) when delayed imaging is performed 2
Why Chest CT is Not Appropriate
The chest is not involved in enterovesical fistula pathophysiology—these fistulas represent abnormal communications between bowel (typically sigmoid colon or terminal ileum) and bladder, confined entirely to the abdominopelvic cavity. 2, 3
Anatomic Considerations
- Fistulas from sigmoid/rectosigmoid disease involve the left or posterior bladder wall 2
- Fistulas from terminal ileum, cecum, or appendix involve the right lateral or anterior bladder wall 2
- The rectum (52%) and sigmoid colon (39%) are the most common sites of origin 4
Alternative and Complementary Imaging
CT Cystography
CT cystography (CT pelvis with bladder contrast) is particularly useful for diagnosing bladder fistulas and leaks, especially colovesical fistulas from sigmoid diverticular disease. 1
- This involves retrograde bladder filling with contrast material 5
- It has supplanted fluoroscopic cystography at most institutions 1
CT Urography (CTU)
CTU may be considered when there is concern for concomitant upper urinary tract pathology or when comprehensive urinary tract evaluation is needed. 1
- Includes unenhanced, nephrographic phase, and excretory phase images 1
- Provides detailed anatomic depiction of kidneys, collecting systems, ureters, and bladder 1
MRI Pelvis
MRI pelvis with IV contrast provides superior soft tissue resolution and is an equivalent alternative to CT for fistula evaluation. 1
- Particularly useful when radiation exposure is a concern 5
- IV gadolinium contrast is essential for detecting active inflammation in fistulous tracts 1
Common Clinical Pitfalls
Symptom Recognition
The classic triad of symptoms should prompt imaging:
- Pneumaturia (passage of air in urine) is present in 88-90% of cases and is the strongest clinical indicator 2, 6
- Fecaluria (passage of fecal material in urine) occurs in 38-43% 4, 6
- Recurrent urinary tract infections are present in 73-88% 4, 6
Imaging Strategy Errors to Avoid
- Do not rely on fluoroscopic contrast enema alone—it has lower detection rates than CT and cannot assess abscesses or surrounding structures 1
- Do not use barium contrast—water-soluble contrast is mandatory 1
- Do not order chest imaging—the pathology is confined to the abdomen and pelvis 2, 3
- Do not skip delayed imaging—immediate post-contrast images may miss the fistulous tract 1
Underlying Etiology Considerations
CT not only detects the fistula but also identifies the underlying cause, which is critical for management planning. 3
Common etiologies include: