What is the best investigation for a patient presenting with pus and discharge from the umbilicus (navel)?

Diagnostic Approach for Umbilical Discharge with Pus

Abdominal ultrasound (US) is the best initial investigation for a patient presenting with pus and discharge from the umbilicus.

Rationale for Ultrasound as First-Line Investigation

Ultrasound offers several advantages as the initial imaging modality for umbilical discharge:

• Non-invasive and readily available in most clinical settings
• No radiation exposure
• Can effectively visualize fluid collections, abscesses, and underlying causes
• Can guide subsequent management decisions
• Cost-effective compared to advanced imaging

Diagnostic Algorithm for Umbilical Discharge

Step 1: Abdominal Ultrasound

• Allows visualization of:
  • Umbilical abscess or fluid collection
  • Potential embryological remnants (urachal remnant, omphalomesenteric duct)
  • Umbilical hernia with potential complications
  • Surrounding soft tissue inflammation

Step 2: Based on Ultrasound Findings

• If definitive diagnosis established: Proceed with appropriate treatment
• If inconclusive or complex findings: Proceed to advanced imaging

Step 3: Advanced Imaging (if needed)

• CT with IV contrast: For better anatomical detail and to identify fistulous tracts 1, 2
• MRI: Superior for evaluating complex cases and fistula tracts 1
• Fistulogram: Only if specific suspicion of fistulous connection that cannot be characterized by cross-sectional imaging 1

Evidence-Based Considerations

The American College of Radiology guidelines support using CT with IV contrast for diagnosing abscesses with a reported sensitivity of 77% 2. However, ultrasound is recommended as the initial investigation for umbilical pathology due to its accessibility and lack of radiation 2, 3.

For umbilical discharge specifically, ultrasound can effectively identify:

• Urachal remnants and infections 4
• Patent vitello-intestinal ducts 5
• Umbilical hernias with complications 6
• Inflammatory and suppurative processes 3

Common Pitfalls to Avoid

1. Skipping imaging entirely: Relying solely on clinical examination may miss important underlying causes such as embryological remnants or fistulas
2. Starting with plain radiographs: Abdominal X-rays have limited value in evaluating umbilical discharge 1
3. Proceeding directly to invasive procedures: Without proper imaging characterization, drainage procedures may be incomplete or miss the underlying cause
4. Failing to consider systemic causes: Some umbilical discharge may be manifestations of systemic conditions like tuberculosis 7

Special Considerations

• For patients with suspected complex fistulous tracts, CT or MRI with contrast should follow the initial ultrasound 1, 2
• In cases where tuberculosis is suspected, chest imaging should also be considered 7
• For recurrent umbilical discharge, a more comprehensive evaluation with cross-sectional imaging is warranted 6

Ultrasound remains the most appropriate first-line investigation, balancing diagnostic accuracy, availability, cost, and patient safety considerations.