Larval cestode infection causing hydatid cysts (E. granulosus) or invasive alveolar masses (E. multilocularis), most commonly involving liver and lung.
Also known as: echinococcosis, hydatid disease, Echinococcus granulosus, Echinococcus multilocularis, cystic echinococcosis, CE, alveolar echinococcosis, AE
Epidemiology
E. granulosus is endemic in sheep- and cattle-raising regions: Mediterranean basin, South America, Central Asia, parts of Africa, Australia, New Zealand. E. multilocularis occurs in the northern hemisphere — central Europe, Russia, China, and parts of North America including Alaska and the upper Midwest. Dogs (and other canids for E. multilocularis: foxes, coyotes) are definitive hosts; humans are accidental intermediate hosts.
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Risk factors
- Residence in or travel to endemic regions
- Close contact with dogs, sheep, or other livestock
- E. multilocularis: outdoor activities in endemic regions, fox or coyote contact, foraging wild berries
- Poor sanitation, ingestion of contaminated food or water
- Occupational exposure: shepherds, hunters, veterinarians
Pathophysiology
Eggs are shed in canine feces and ingested by humans. Oncospheres hatch in the duodenum, penetrate the bowel wall, and travel through the portal circulation to organs. Most lodge in the liver (first capillary filter), then lung. E. granulosus forms a slowly enlarging, well-circumscribed hydatid cyst with germinal layer and laminated membrane, often with daughter cysts. E. multilocularis grows by exogenous budding without a clear capsule, infiltrating tissue and metastasizing to other organs in a manner that resembles malignancy.
Clinical presentation
Symptoms
- Cystic echinococcosis (CE) — many cysts are asymptomatic for years and detected incidentally
- Hepatic CE: RUQ pain or mass, biliary obstruction, cholangitis if cyst ruptures into biliary tree
- Pulmonary CE: chronic cough, chest pain, hemoptysis, expectoration of cyst contents ('grape skins') if ruptures
- Cyst rupture: acute pain, anaphylaxis from sudden release of antigen, dissemination of daughter cysts
- Alveolar echinococcosis (AE) — insidious RUQ pain, weight loss, jaundice, hepatomegaly mimicking malignancy
- AE can metastasize to lung, brain, bone with corresponding symptoms
Signs / physical exam
- Hepatomegaly, palpable cyst, tenderness
- Jaundice with biliary involvement
- Pulmonary findings depending on cyst size and location
- Eosinophilia (variable; often absent in intact cysts; rises with leakage)
- Anaphylaxis on cyst rupture
Classic findings
Patient from a sheep- or cattle-raising region with a well-circumscribed liver or lung cyst, often containing daughter cysts ('honeycomb' or 'cartwheel' pattern) and detached germinal membranes ('water lily sign' on imaging). AE shows infiltrative, irregular, vesicular hepatic lesions that mimic malignancy.
Differential diagnosis
- Hepatic abscess (pyogenic or amebic) — Acute febrile illness, leukocytosis; ultrasound and aspiration distinguish; amebic serology
- Hepatic tumor (HCC, metastasis, cystadenoma) — Imaging characteristics, AFP, tissue diagnosis if uncertain
- Simple hepatic cyst or polycystic liver disease — No daughter cysts; serology negative
- Tuberculous abscess — Endemic exposure; AFB testing
- Pulmonary hydatid versus lung abscess, malignancy, fungal disease — Cyst morphology, serology
- Alveolar echinococcosis versus cholangiocarcinoma or HCC — Infiltrative pattern with vesicles can mimic malignancy; serology and biopsy
Diagnostic workup
Diagnostic criteria
Compatible imaging plus positive serology is sufficient for diagnosis in most cases. Definitive diagnosis from cyst contents or biopsy in atypical cases (with caution due to anaphylaxis and seeding risk).
Labs
- Echinococcus serology — IgG ELISA, indirect hemagglutination, immunoblot; sensitivity higher for hepatic than pulmonary CE; AE typically strongly seropositive
- CBC: eosinophilia variable
- LFTs, BMP
- CA 19-9 may be elevated in AE
- Avoid percutaneous biopsy / aspiration of intact suspected hydatid cyst without preparation — risk of anaphylaxis and dissemination
- PAIR procedure (Puncture-Aspiration-Injection-Reaspiration) under albendazole cover is therapeutic for selected cysts
Imaging
- Abdominal ultrasound — first-line; WHO/IWGE classification (CE1 through CE5) based on cyst morphology
- Daughter cysts within mother cyst, hydatid sand, water lily sign (detached endocyst), eggshell calcification
- Chest x-ray and CT for pulmonary cysts
- MRI for complex hepatic disease and AE characterization
- PET-CT useful for monitoring AE activity
- Brain imaging in selected disseminated cases
Treatment
First-line
- Cystic echinococcosis treatment is stage- and cyst-specific (WHO/IWGE):
- CE1, CE2, CE3a, CE3b active/transitional cysts — treatment options include surgery, PAIR (puncture-aspiration-injection-reaspiration with scolicidal agent), or albendazole, depending on size, location, and complications
- Albendazole 10-15 mg/kg/day (typically 400 mg PO BID with fatty meal) for 3-6 months minimum, sometimes longer or cyclical (28 days on, 14 days off) — used pre- and post-operatively and as primary therapy for inoperable disease
- Surgical resection (open or laparoscopic) — definitive for large symptomatic cysts; risk of intraoperative anaphylaxis and spillage; use scolicidal agents intraoperatively
- PAIR for selected uncomplicated unilocular hepatic cysts: needle puncture under ultrasound with albendazole coverage
- CE4, CE5 (inactive/calcified): observation; no antihelminthic required
- Alveolar echinococcosis: complete radical surgical resection when feasible (margins like cancer surgery), with continuous albendazole for at least 2 years post-surgery and lifelong monitoring; if unresectable, lifelong albendazole
- Liver transplantation considered for severe nonresectable AE
Second-line / adjunct
- Mebendazole 40-50 mg/kg/day in divided doses — alternative when albendazole intolerant
- Praziquantel sometimes added in perioperative period (protoscolicidal)
- Endoscopic management of biliary complications (ERCP for cyst-biliary fistula)
- Multidisciplinary management at centers with experience in echinococcal disease
Complications
- Cyst rupture with anaphylaxis (especially during surgery, trauma, or PAIR)
- Secondary echinococcosis from spillage of daughter cysts
- Cholangitis and biliary obstruction from cyst-biliary communication
- Hemoptysis and pulmonary infection from ruptured pulmonary cysts
- Progressive liver failure or cholangiocarcinoma-like presentation in AE
- Recurrence after incomplete surgical or medical treatment
PANCE pearls
- Cystic echinococcosis (E. granulosus) makes well-defined cysts with daughter cysts; alveolar echinococcosis (E. multilocularis) is infiltrative and mimics malignancy.
- Never aspirate or biopsy a suspected hydatid cyst without antihelminthic coverage and preparation for anaphylaxis.
- WHO/IWGE ultrasound staging (CE1-CE5) directly guides whether to treat with surgery, PAIR, albendazole, or observation.
- Albendazole is the antihelminthic of choice and is used pre-/post-operatively to reduce recurrence after surgery.
- Alveolar echinococcosis behaves like a cancer — treat with radical surgery when possible plus prolonged albendazole and indefinite follow-up.
References
- WHO/IWGE 2010 — WHO Informal Working Group on Echinococcosis: Expert consensus for the diagnosis and treatment of cystic and alveolar echinococcosis in humans (Brunetti et al., Acta Trop 2010)
- CDC — CDC Parasites — Echinococcosis: clinical features, diagnosis, and treatment
- ESCMID — European guidance on management of echinococcosis
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