What is the approach to assessing a urinary tract infection (UTI) due to colovesical fistula, including definition, differential diagnosis, history, physical examination, investigations, empiric treatment, and indications for referral?

Assessment of UTI Due to Colovesical Fistula

Definition

Colovesical fistula (CVF) is an abnormal pathological communication between the colon and urinary bladder, most commonly presenting with the pathognomonic triad of pneumaturia, fecaluria, and recurrent urinary tract infections. 1, 2

• Represents a complicated UTI requiring surgical evaluation in most cases 2
• Most common cause is complicated diverticular disease (60-70% of cases), followed by colorectal cancer, Crohn's disease, radiation therapy, and iatrogenic injury 2, 3

Differential Diagnosis

• Diverticular disease (most common) 2, 3
• Colorectal carcinoma 4, 2
• Bladder cancer with colonic invasion 2
• Crohn's disease 1, 3
• Radiation-induced fistula 5, 3
• Metastatic cancer from distant sites (rare - lung, etc.) 5
• Iatrogenic injury (post-surgical) 2
• Lymphoma 5

History

Classic Presentation

• Pneumaturia (passage of gas in urine) - pathognomonic 1
• Fecaluria (passage of fecal matter in urine) - pathognomonic 1, 4
• Recurrent UTIs despite appropriate antibiotic therapy 4, 2, 3
• Dysuria and urinary frequency 5
• Abdominal pain (particularly left lower quadrant) 5
• Hematuria 5

Red Flags

• Constitutional symptoms (fever, weight loss, night sweats) suggesting malignancy 4
• Severe sepsis or high-grade fever indicating complicated UTI 6
• Uncontrolled diabetes, organ failure, or immunosuppression (increases risk of atypical organisms) 4
• History of pelvic radiation 2, 5

Risk Factors

• Known diverticular disease 2, 3
• History of colorectal or bladder malignancy 2, 5
• Inflammatory bowel disease (especially Crohn's) 1, 3
• Prior pelvic surgery or radiation 2, 5
• Advanced age (>60 years) 4
• Male gender (more common presentation in men) 3

Physical Examination

Focused Abdominal Examination

• Left lower quadrant tenderness (suggests diverticular etiology) 5
• Palpable abdominal mass (suggests malignancy or abscess) 2
• Signs of peritonitis (guarding, rebound) indicating perforation 2

Genitourinary Examination

• Suprapubic tenderness 6
• Digital rectal examination for masses, tenderness, or blood 3

General Assessment

• Vital signs for sepsis (fever, tachycardia, hypotension) 6
• Nutritional status and frailty assessment (impacts surgical candidacy) 6

Investigations

Laboratory Studies

• Urinalysis with microscopy: severe bacteriuria, pyuria, possible fecal debris 6
• Urine culture: typically shows E. coli or mixed enteric organisms; atypical organisms (e.g., Lactococcus lactis) suggest serious underlying disease 4
• Complete blood count: leukocytosis, anemia (if malignancy) 6
• Inflammatory markers: elevated CRP, procalcitonin (indicates severity of infection) 6
• Renal function tests: assess for obstructive uropathy 6

Primary Imaging Modality

CT imaging is the primary diagnostic modality for suspected colovesical fistula. 7, 1

CT Urography (CTU)

• First-line investigation for recurrent complicated UTIs 7
• Includes unenhanced, nephrographic, and excretory phases 7
• Detects fistula in >80% of cases and identifies underlying etiology 7

CT Cystography

• Preferred for definitive diagnosis of colovesical fistula 7, 1
• Accurately detects and characterizes fistula in >80% of patients 7
• Provides size and location information for surgical planning 7, 1
• Has supplanted fluoroscopic cystography 7

CT Abdomen/Pelvis with Contrast

• Add rectal or oral contrast with delayed scanning to detect enterovesical fistulas 7, 1
• Critical for identifying infected fistulous tracts 7, 1

Expected CT Findings

• Intravesical gas (air in bladder) 6
• Focal bladder wall thickening adjacent to colonic pathology 4, 6
• Colonic wall thickening or mass contiguous with bladder 4, 6
• Direct visualization of fistulous tract (in minority of cases) 7
• Pelvic abscess (if present) 2

Alternative/Adjunctive Imaging

• MRI abdomen/pelvis: equally sensitive to CT for enterovesicular fistulae with superior soft-tissue contrast 7, 1
• MRI particularly useful when repeat imaging needed or to clearly delineate fistula anatomy 7, 6
• Fluoroscopic cystography: alternative with dynamic evaluation and greater spatial resolution 7
• Contrast enema: less sensitive than CT; water-soluble contrast preferred over barium 7

Endoscopic Evaluation

• Cystoscopy: best investigation to confirm presence of fistula; may visualize fistulous opening 3
• Colonoscopy: identifies colonic pathology (diverticula, mass, stricture) and may demonstrate fistula with contrast 6, 3

Empiric Treatment

Antibiotic Therapy

• Initiate broad-spectrum antibiotics covering enteric organisms (e.g., sulbactam/ampicillin, piperacillin-tazobactam, or fluoroquinolone plus metronidazole) 6
• Tailor antibiotics based on urine culture and sensitivities 4, 6
• Duration: typically 7-14 days for complicated UTI, but definitive treatment requires fistula closure 6

Supportive Care

• Urinary catheterization may be needed for bladder drainage 2
• Fluid resuscitation if septic 6
• Nutritional support: consider location of fistula (distal fistulas may tolerate enteral nutrition; proximal may require parenteral nutrition) 1

Non-Surgical Management (Selected Cases Only)

• Reserved for patients unfit for surgery due to severe comorbidities or frailty 2, 6
• Defunctioning colostomy alone may improve quality of life in non-surgical candidates 2
• Covered colonic stent (experimental): may seal fistula in palliative cases 6

Indications to Refer

Urgent Surgical Referral

• All patients with confirmed colovesical fistula should be referred to colorectal surgery 2, 3
• One-stage resection and anastomosis is preferred approach for most patients 2, 3
• Multi-stage procedure reserved for: pelvic abscess, advanced malignancy, or prior radiation therapy 2

Urgent Urology Referral

• Concurrent with surgical referral for cystoscopy and bladder assessment 3
• Bladder repair typically involves simple closure after colonic resection 2

Oncology Referral

• If malignancy suspected or confirmed on imaging or endoscopy 4, 5
• Metastatic disease requires palliative care planning 6, 5

Gastroenterology Referral

• For colonoscopy to identify colonic pathology 6, 3
• Crohn's disease management if inflammatory bowel disease is etiology 1

Critical Pitfalls

Diagnostic Pitfalls

• Do NOT rely on non-contrast CT alone - delayed imaging after contrast administration is essential 1
• Always consider adding rectal contrast when enterovesical fistula is in the differential 7, 1
• Atypical organisms on urine culture (e.g., Lactococcus lactis) should prompt investigation for serious underlying disease including malignancy 4
• Negative initial imaging does not exclude fistula - consider MRI or cystoscopy if clinical suspicion remains high 7, 6
• Barium enema is contraindicated - use water-soluble contrast only 7

Management Pitfalls

• Do NOT treat recurrent UTIs with antibiotics alone without investigating for structural abnormality 2, 3
• Avoid prolonged conservative management in surgical candidates - definitive treatment requires fistula closure 2
• Do NOT assume diverticular disease - always rule out malignancy with colonoscopy and tissue diagnosis 4, 5, 3
• Failure to recognize metastatic disease from distant sites (e.g., lung cancer) can delay appropriate palliative care 5
• Underestimating surgical complexity - patients with pelvic abscess, radiation history, or malignancy require specialized surgical planning 2
• Missing nutritional implications in Crohn's disease patients with fistulas - location determines feeding strategy 1