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Hydatid Disease of the Lung

(Pulmonary Echinococcosis / Pulmonary Hydatidosis)

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1. DEFINITION

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2. AETIOLOGY & LIFE CYCLE

Life Cycle (Stepwise)

1. Dog (definitive host) harbours adult tapeworm in small intestine → sheds oncospheres (eggs) in faeces
2. Humans ingest eggs (contaminated food, water, soil — faeco-oral route)
3. Eggs hatch in duodenum → oncospheres penetrate gut wall → enter portal circulation
4. First filter = Liver (60–70%) → eggs that pass through → Second filter = Lungs (20–30%)
5. Larvae develop into hydatid cysts over months to years
6. Dog ingests infected sheep viscera → cycle continues

Why the Lung is More Commonly Affected in Children

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3. PATHOLOGY

Structure of the Cyst (3 Layers)

Contents

• Hydatid fluid — crystal clear, "rock water"; contains proteins (antigen B, 5), polysaccharides; sterile under normal conditions
• Daughter cysts — endogenous daughter cysts budding inward from germinal layer
• Brood capsules — contain scolices

Cyst Size

• Ranges from 1 cm to >20 cm; lung cysts tend to grow faster than liver cysts (lung parenchyma offers less resistance)

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4. CLINICAL FEATURES

A. Uncomplicated Cyst

B. Complicated Cyst (Rupture)

• Into bronchus (most common): sudden violent cough, expectoration of salty/bitter fluid (hydatid fluid), grape-skin membranes ("salty water + white membranes"), relief of symptoms
• Into pleural cavity: hydropneumothorax, anaphylaxis
• Rupture + infection: abscess formation, fever, purulent sputum
• Anaphylaxis (life-threatening): urticaria, bronchospasm, shock — due to sudden release of hydatid antigens
• Secondary seeding ("hydatid shower"): dissemination of scolices → new cysts

C. Signs

• Chest expansion reduced ipsilaterally
• Dull percussion note
• Reduced breath sounds
• Rarely: features of respiratory distress

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5. INVESTIGATIONS

A. Haematology

• Eosinophilia (10–40%) — in ~25% of cases; classical but not constant
• Leukocytosis if infected

B. Serology

Serology is less sensitive for pulmonary than hepatic hydatid (lung cysts may not leak antigen)

C. Radiology

Plain Chest X-Ray

CT Scan (Investigation of Choice)

• Defines cyst wall, daughter cysts, relationship to bronchi/vessels
• Detects early rupture before X-ray changes
• Identifies bilateral/multiple cysts
• "Water-lily sign" on CT = pathognomonic of ruptured hydatid

MRI

• Superior soft-tissue detail; useful for complex or chest wall involvement
• Ectocyst appears as hypointense rim on T2 ("dark ring sign")

Bronchoscopy

• Rarely performed; may reveal hooklets/scolices if rupture has occurred

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6. DIFFERENTIAL DIAGNOSIS

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7. TREATMENT

A. Surgical (Gold Standard)

Principles of Surgery

1. Protect the field — packs soaked in hypertonic saline (20%) or cetrimide around cyst to kill any spilled scolices and prevent dissemination
2. Puncture, Aspiration, Injection, Re-aspiration (PAIR) or controlled evacuation
3. Remove contents, sterilize cavity, manage residual space

Surgical Techniques

Key Intraoperative Caution

• Never aspirate without field protection — spillage causes anaphylaxis and secondary seeding
• Sterilize with 20% NaCl (hypertonic saline), 0.5% cetrimide, or 95% ethanol injected into cyst before removal
• Close all bronchial communications to prevent postoperative air leak

B. Medical Treatment

• Dose: 400 mg twice daily (15 mg/kg/day) in cycles of 28 days on, 14 days off
• Duration: 3–6 cycles minimum
• Mechanism: Inhibits tubulin polymerisation → disrupts larval glucose uptake → cyst death
• Used: Pre-operatively (reduces cyst viability, prevents seeding), post-operatively (prevents recurrence), inoperable cases

C. PAIR (Puncture-Aspiration-Injection-Re-aspiration)

• Primarily for hepatic hydatid; used cautiously in lung (risk of anaphylaxis, bronchopleural fistula)
• Not recommended for pulmonary hydatid as standard practice

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8. COMPLICATIONS

Of the Disease

Of Surgery

• Haemorrhage
• Bronchopleural fistula
• Empyema
• Recurrence (if seeding occurs)
• Residual cavity infection

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9. PROGNOSIS

• Uncomplicated cysts: excellent prognosis with surgery (recurrence <5% with adequate technique)
• Ruptured/infected cysts: higher morbidity; risk of dissemination
• Bilateral cysts: staged surgery — worse prognosis
• Post-operative albendazole for 3 months reduces recurrence
• Overall surgical mortality: <1% in elective cases

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10. SPECIAL POINTS (HIGH YIELD for MD Exams)

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11. SUMMARY (Mnemonic: "ECLAT")

• E — Echinococcus granulosus (dog-sheep cycle)
• C — Cyst (3 layers: Pericyst, Ectocyst, Endocyst)
• L — Lung (2nd most common organ; right > left; lower > upper)
• A — Albendazole (pre/post-op) + Surgery (Capitonnage)
• T — Tell-tale signs: Water-lily sign, Meniscus sign, Eosinophilia

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