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
Overview
Zoonotic infection by larval stages of the tapeworm Echinococcus. Cystic echinococcosis (CE) is caused by E. granulosus and produces well-circumscribed hydatid cysts, most commonly in liver and lung. Alveolar echinococcosis (AE) is caused by E. multilocularis and behaves like a slowly growing malignancy with infiltrative liver disease and distant metastases.
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.
Try a board-style Echinococcosis question
Real questions from the FirstPassPA bank, with the full explanation. Pick an answer — no signup, no email.
Question 1Infectious DiseaseMedium
A 45-year-old sheep rancher who also keeps herding dogs is evaluated for months of vague right-upper-quadrant fullness. Ultrasound and CT show a large, well-defined cystic liver lesion with a calcified rim and several smaller 'daughter' cysts within it. Serology for the responsible parasite is positive, and eosinophilia is present. Which of the following is the most likely diagnosis?
APyogenic liver abscess
BHepatic hydatid cyst
CAmebic liver abscess
DSimple hepatic cyst
Reveal answer & full explanation
Correct answer: B — Hepatic hydatid cyst
APyogenic liver abscess
BHepatic hydatid cyst✓
CAmebic liver abscess
DSimple hepatic cyst
Why Hepatic hydatid cyst is correct
Cystic echinococcosis (hydatid disease) is caused by the larval stage of Echinococcus granulosus.
Humans are accidental intermediate hosts who ingest eggs shed by dogs (definitive host) in sheep-raising regions.
The larvae form slow-growing hepatic cysts, and the imaging is characteristic: a large unilocular cyst with a calcified wall and internal daughter cysts, often with eosinophilia and positive serology.
Why the others are wrong
Pyogenic liver abscess — presents acutely with fever and leukocytosis and shows a complex fluid collection, not a calcified cyst with daughter cysts.
Amebic liver abscess — follows Entamoeba histolytica exposure and yields 'anchovy paste' aspirate, typically a single subacute lesion without a calcified daughter-cyst structure.
Simple hepatic cyst — is an anechoic, thin-walled cyst with no septations, daughter cysts, calcification, or eosinophilia.
🔒 Free preview limit reached
Keep reading — start your free trial
You've read your 2 free diagnosis previews. Create your free account to unlock the full Echinococcosis (Hydatid Disease) outline — plus all 514 diagnoses, 6,500+ board-style questions, flashcards, and an AI tutor. Your 7-day free trial includes everything, and there's no credit card required.
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
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
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)
Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA or PAEA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants; End of Rotation™ is a program of the Physician Assistant Education Association.