What is an enterocutaneous (EC) scan?

What is an Enterocutaneous (EC) Scan?

An enterocutaneous (EC) scan is an imaging study that evaluates abnormal connections (fistulas) between the intestinal tract and the skin surface, typically using CT enterography or MRI with specialized protocols to visualize the fistula tract, origin, and associated complications. 1

Definition and Clinical Context

An enterocutaneous fistula is defined as an abnormal communication between the bowel lumen and the skin surface. EC fistulas are classified based on:

• Anatomy: Indicating the bowel segment of origin followed by the target organ (e.g., ileocutaneous, colocutaneous) 1
• Output volume: 1
  • Low: < 200 ml/day
  • Moderate: 200-500 ml/day
  • High: > 500 ml/day

Imaging Techniques for EC Fistula Evaluation

CT Enterography

• Preferred technique for initial evaluation due to excellent diagnostic performance (sensitivity 75-90%, specificity >90%) 1, 2
• Technical parameters: 1, 2
  • Thin collimation (2-3mm slice thickness)
  • Multiplanar reconstruction
  • IV contrast administration with imaging timed between enteric and portal phases (50-70 seconds)
  • Large volumes (1300-1800cc) of neutral oral contrast
  • Complete imaging coverage including abdomen, pelvis, and perineum

MR Enterography

• Alternative to CT with advantages of no radiation exposure and better soft tissue contrast 1
• Particularly useful for evaluating perianal disease and complex fistula networks
• Can better differentiate between active inflammation and fibrosis in associated strictures

Fistulography

• Direct injection of contrast into the external fistula opening under fluoroscopic guidance
• May be combined with nuclear medicine techniques (e.g., Tc-99m DTPA SPECT/CT) for better delineation 3

Imaging Findings in EC Fistulas

On cross-sectional imaging, EC fistulas appear as: 1

• Tubular structures arising from the bowel wall
• May contain fluid, air, or both
• Peripheral contrast enhancement
• Connection between bowel segment and skin surface

Key features to identify and report: 1

• Fistula origin (bowel segment involved)
• Fistula tract course and complexity
• Associated complications:
  • Strictures
  • Abscesses
  • Inflammatory masses
  • Additional fistulous connections

Clinical Applications and Importance

EC scans are critical for: 1, 4, 5

1. Determining the exact anatomy of the fistula tract
2. Identifying the underlying cause (e.g., Crohn's disease, postoperative complication, trauma)
3. Planning appropriate treatment (medical management vs. surgical intervention)
4. Monitoring response to treatment

Common Pitfalls and Considerations

• Complete imaging coverage: Ensure the entire abdomen, pelvis, and perineum are included 1
• Optimal bowel distention: Inadequate bowel distention may obscure small fistulas 1, 2
• Timing of contrast: Proper timing of IV contrast administration is crucial for visualizing active inflammation 2
• Patient preparation: Large volumes of oral contrast may not be tolerated in acutely ill patients 1
• Interpretation challenges: Differentiating between active inflammation and fibrosis in associated strictures 1

EC scans play a vital role in the multidisciplinary management of enterocutaneous fistulas, providing crucial anatomical information that guides treatment decisions and improves patient outcomes.