What is the diagnosis of a colonic fistula (abnormal connection in the colon)?

From the Guidelines

Colonial fistulas are diagnosed through a combination of clinical evaluation and imaging studies, with MRI being the most effective modality for perianal and rectovaginal fistulas, as it provides detailed soft tissue visualization 1. The diagnostic process typically begins with a thorough medical history and physical examination, focusing on symptoms such as abdominal pain, unexplained fever, altered bowel habits, or drainage from abnormal openings.

• A complete physical examination, including a digital rectal examination, is usually feasible, but in some cases, sedation or anesthesia may be needed due to the intense pain 1.
• Laboratory tests, including complete blood count, C-reactive protein, and erythrocyte sedimentation rate, help evaluate inflammation, and are particularly useful in patients with signs of systemic infection or sepsis 1.
• Imaging studies, such as CT scan or endosonography, can be useful in specific situations, such as atypical presentation, suspicion of occult supralevator abscesses, complex anal fistula, or perianal Crohn’s disease 1.
• Fistulography, where contrast is injected directly into the external opening, can help map the fistula's course, and colonoscopy is essential to visualize the internal opening and assess for inflammatory bowel disease, diverticulitis, or malignancy as potential causes.
• The choice of imaging modality should take into account multiple factors, such as patient’s past medical history, clinical presentation, local availability of resources, and skills 1.
• Diagnosis should be prompt as fistulas rarely heal spontaneously and typically require surgical intervention after controlling any active infection with appropriate antibiotics 1.

From the Research

Diagnosis of Colonial Fistula

• The diagnosis of colonic fistulae is crucial in defining the best therapeutic approach 2
• Fistulae can be suspected from clinical history or specific symptoms, but imaging plays a key role in confirming the diagnosis 2
• Common symptoms of colovesical fistula include pneumaturia and faecaluria, which were present in 90.1% of cases 3

Imaging Techniques

• CT Colonography is considered the best radiologic test to evaluate the colon, and has potential in evaluating patients with suspected colonic fistulae 2
• CT scan is the most frequently performed investigation and is most sensitive in detecting the fistula and underlying aetiology 4
• Barium enema was the most sensitive test to detect stricture formation, and colonic endoscopy was the most reliable means of excluding a colonic malignancy 3
• MRI may also be used in special circumstances, and invasive procedures such as endoscopy can assist in the evaluation of mucosal surfaces 5

Diagnostic Approach

• The diagnosis of colovesical fistula is predominately a clinical one, and patients with a suspected fistula are often over-investigated 3, 4
• A high suspicion of a fistula can usually be obtained from an accurate clinical history 4
• Investigations should be focused on determining aetiology rather than demonstrating the fistulous tract itself 4
• CT and lower gastrointestinal endoscopy are proposed as sufficient investigations in the majority of cases 4