Hydatid Cyst

Introduction

Hydatid disease (cystic echinococcosis) is a zoonotic infection caused by the larval stage of the tapeworm Echinococcus granulosus. It is characterized by the formation of cystic lesions, predominantly in the liver and lungs.

Epidemiology and Life Cycle

• Definitive Host: Dogs and other canines (harbor adult worms in intestine).
• Intermediate Host: Sheep, cattle, goats, pigs (harbor larval cysts in viscera).
• Accidental Host: Humans. Infection occurs via fecal-oral route through ingestion of eggs from contaminated food, water, or direct contact with dogs.
• Pathogenesis: Ingested eggs hatch in the small intestine, releasing oncospheres that penetrate the mucosa and disseminate via portal circulation.
  • Liver: First filter (60-70% of cysts).
  • Lungs: Second filter (20-25% of cysts).
  • Systemic: Brain, bone, kidney, spleen, etc.

Clinical Manifestations

Symptoms depend on the size, location, and status (intact vs. ruptured) of the cyst.

• Liver Cysts: Often asymptomatic for years. May present with hepatomegaly, right upper quadrant pain, or a palpable mass. Rupture into the biliary tree causes obstructive jaundice and cholangitis.
• Lung Cysts: Cough, chest pain, dyspnea, or hemoptysis. Rupture into a bronchus leads to expectoration of salty fluid and grape-skin-like membranes.
• Anaphylaxis: Spontaneous or traumatic rupture can release cyst fluid, causing fever, urticaria, and potentially fatal anaphylactic shock.

Diagnosis

1. Imaging (Gold Standard):
   • Ultrasonography (USG): The primary modality for hepatic cysts. It allows for staging (WHO classification) which guides management.
     • CE1 & CE2: Active cysts (unilocular or multivesicular).
     • CE3: Transitional cysts (detachment of membrane).
     • CE4 & CE5: Inactive cysts (solid/calcified).
   • CT/MRI: Useful for lung, CNS, and bone cysts, and for evaluating anatomical relationships/biliary communication before surgery.
2. Serology: ELISA or Hemagglutination tests detect antibodies. Sensitivity varies (lower for lung/calcified cysts). Useful for confirmation but negative serology does not rule out disease.
3. Aspiration: Diagnostic aspiration is generally contraindicated due to risks of anaphylaxis and spillage (secondary dissemination), unless done as part of the PAIR procedure.

Management

Management is stage-specific and multimodal, involving chemotherapy, percutaneous procedures, and surgery.

1. Medical Management (Chemotherapy)

• Indications:
  • Small, uncomplicated cysts (<5 cm).
  • Inoperable patients or disseminated disease (peritoneal/multiple organs).
  • Adjunct Therapy: Essential pre- and post-procedure (surgery or PAIR) to prevent recurrence from spillage (secondary echinococcosis).
  • Prevention of recurrence after rupture.
• Drugs:
  • Albendazole (Drug of Choice):
    • Dose: 15 mg/kg/day orally in 2 divided doses (Max 800 mg/day).
    • Administration: Must be taken with a fatty meal to improve absorption.
    • Duration: Traditionally given in 4-week cycles with 2-week drug-free intervals to monitor toxicity, typically for 3–6 months (1-month pre-op and 1–3 months post-op is common). Continuous therapy is now often preferred to cyclic therapy.
    • Monitoring: CBC (leukopenia) and Liver Function Tests (hepatotoxicity) every 2 weeks.
  • Praziquantel: Used as an adjunct (40 mg/kg/week) to kill protoscoleces, particularly peri-operatively or after spillage. It increases albendazole blood levels.

2. Percutaneous Treatment (PAIR)

PAIR stands for Puncture, Aspiration, Injection, Re-aspiration.

• Procedure: Under USG/CT guidance, the cyst is punctured, fluid is aspirated, a scolicidal agent (e.g., 95% ethanol or 20% hypertonic saline) is injected and left for 15-20 minutes, and then re-aspirated.
• Indications:
  • Uncomplicated hepatic cysts (CE1 or CE3a) >5 cm.
  • Patients who are poor surgical candidates.
  • Those who refuse surgery.
• Contraindications:
  • Lung cysts (risk of bronchial fistula).
  • Cysts communicating with the biliary tree (risk of sclerosing cholangitis from scolicidal agent).
  • Inaccessible or superficial cysts (risk of rupture).
  • Inactive/calcified cysts (CE4, CE5).
• Coverage: Peri-procedural Albendazole is mandatory (start 4 days to 1 week prior and continue for 1 month).

3. Surgical Management

Surgery remains the treatment of choice for complex cases. The goal is complete removal without spillage.

• Indications:
  • Lung cysts (all sizes).
  • Large liver cysts (>10 cm) or superficial cysts at risk of rupture.
  • Complicated cysts (rupture, infection, biliary communication).
  • Cysts pressing on vital structures.
  • Complex multivesicular cysts (CE2, CE3b).
• Techniques:
  • Conservative: Cystectomy or endocystectomy (removal of germinal/laminar layers leaving pericyst). Capitonnage or omentoplasty is used to manage the residual cavity.
  • Radical: Pericystectomy or hepatic resection (lower recurrence but higher morbidity).
• Precautions: Operative field must be protected with gauze soaked in scolicidal agents (hypertonic saline) to prevent seeding if rupture occurs.
• Laparoscopy: Increasingly used for selected liver cysts.

4. "Watch and Wait" Strategy

• Indication: Inactive, solid, or calcified cysts (WHO stage CE4 and CE5).
• Rationale: These cysts are biologically inactive and often remain stable or regress. Treatment carries risks with no clear benefit.
• Follow-up: Long-term ultrasound monitoring.

Organ-Specific Considerations

• Liver Cysts: Managed by PAIR, Surgery, or Chemotherapy based on staging.
• Pulmonary Cysts:
  • Surgery is the gold standard (parenchyma-sparing cystectomy).
  • PAIR is Contraindicated.
  • Chemotherapy: Used for small cysts or if surgery is not possible, but response is slower. Post-op albendazole is given for 3–6 months if spillage occurs.

Prevention

• Hygiene: Hand washing, washing vegetables.
• Control: Deworming dogs (praziquantel), preventing dogs from eating offal (sheep carcasses/viscera).
• Safe water supply.