Investigations for Hydatid Cyst (Echinococcosis)

1. Laboratory Investigations

Haematological

• Complete Blood Count (CBC): Eosinophilia is present in approximately 35% of cases. It is more marked if the cyst has leaked or ruptured. WBC count is usually normal (<10,000/mm³ in ~10% of cases).
• Serum bilirubin: Elevated (>2 mg/dL) in ~20% of patients, especially if there is biliary communication.
• Liver Function Tests (LFTs): Elevated if bile ducts are involved.

Serological Tests (Immunological)

Note: Eosinophilia is not a reliable feature unless the cyst ruptures. Blood chemistry changes are usually absent in uncomplicated cysts. - Goldman-Cecil Medicine

2. Imaging Investigations

Ultrasound (USG) - First-line Investigation

• Most commonly used worldwide due to availability, affordability, and ~90% specificity.
• Can show:
  • Simple cyst with budding membrane signs and free-floating hydatid sand (hyperechogenic)
  • Rosette appearance when daughter cysts are present
  • Calcification of the wall - highly suggestive of hydatid disease
  • Split wall (floating membrane), honeycomb septa
• Gharbi Classification on USG:
  • Type I - Pure fluid collection
  • Type II - Fluid with split wall (floating membrane)
  • Type III - Fluid with septa (honeycomb image)
  • Type IV - Heterogeneous echographic patterns
  • Type V - Reflecting thick walls (calcified/dead cyst)

CT Scan

• Similar information to ultrasound, but provides more specific details about location and depth within the liver.
• Clearly visualizes daughter cysts and exogenous cysts; allows volume estimation.
• Imperative for operative planning, especially for laparoscopic approach.
• Shows calcification, peripheral focal areas, and fluid density depending on proteinaceous content.

Chest X-Ray (CXR)

• Limited value.
• May show: elevated diaphragm, concentric calcifications in cyst wall.
• Important to look for pulmonary hydatid cysts (25% of cases involve lungs).

MRI

• Provides excellent structural detail of the cyst.
• Adds little over ultrasound/CT for routine cases; more expensive.
• Useful when soft tissue characterization is needed.

ERCP (Endoscopic Retrograde Cholangiopancreatography)

• Demonstrates communication between cysts and bile ducts.
• Used to drain the biliary tree pre-operatively.
• Advocated by some to completely define bile duct anatomy and visualize clinically silent biliary connections.

3. Summary Table

Key point: Percutaneous needle aspiration/biopsy is contraindicated because of the risk of rupture, spillage of scoleces (seeding), and potentially fatal anaphylaxis. Diagnosis is established by imaging + serology.