Hydatid Disease
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Direct answer
A hydatid cyst is the larval stage of Echinococcus granulosus, acquired from dog faeces, that behaves in the liver like a slow-growing benign tumour: a right-lobe, well-defined, multiseptate cyst with daughter cysts, often silent for years and picked up on ultrasound. Diagnosis rests on imaging plus hydatid serology (ELISA; the Casoni intradermal test is largely historical), and management is albendazole-covered intervention — open cyst evacuation with a scolicidal agent or hepatic resection for complicated cysts, or PAIR (puncture, aspiration, injection, reaspiration) for selected uncomplicated cysts in poor surgical candidates. The two surgical emergencies are anaphylaxis from cyst rupture or spillage, and cholangitis from a cysto-biliary communication.
What you must remember
- Host cycle: dog is the definitive host, sheep (or cattle) the intermediate; man is an accidental dead-end intermediate. In India the burden clusters in sheep-rearing belts — Kashmir, Andhra Pradesh, Telangana and parts of Tamil Nadu — among pastoralists, slaughterhouse workers and children with dog contact.
- Organ order: liver about 70 per cent (right lobe predominant), lung about 20 per cent, then kidney, spleen, bone, brain. Lung cysts in children are relatively more common than textbooks for adults suggest.
- Cyst architecture: germinal layer broods daughter cysts (the pathognomonic finding); endocyst (germinal + laminated membrane) is the parasite, pericyst is the host fibrous reaction. A detached floating membrane gives the water-lily sign on ultrasound.
- Investigation ladder: ultrasound first (WHO ultrasound classification guides management), ELISA for hydatid antibody (sensitivity high for liver, poor for lung and extrahepatic disease), CT for anatomy and calcification, MRCP when a biliary communication is suspected. Casoni test is no longer standard.
- Drug dosing: albendazole 15 mg/kg/day in two divided doses (adults commonly 400 mg twice daily), generally started days to weeks before intervention and continued 1-6 months after; PAIR requires albendazole cover before and after puncture.
- Scolicidal agents: 20 per cent hypertonic saline or 95 per cent alcohol instilled after aspiration; formalin is abandoned (causes sclerosing cholangitis if a biliary communication exists).
- Cysto-biliary communication red flags: jaundice, cholangitis, urticaria with fever, bilious or bile-stained aspirate, and cyst-bile communication on MRCP/ERCP — these mandate exploration, bile duct clearance and often a definitive hepatic resection rather than simple evacuation.
- Never forget: rupture or spillage during handling can cause anaphylaxis and disseminated disease, so the field is protected with hypertonic-saline-soaked mops before aspiration.
A worked liver cyst case
A 35-year-old shepherd from Anantapur has a dull right hypochondrial ache; ultrasound shows a 10 cm right-lobe cyst with daughter cysts and a mobile membrane. Serology is positive. Steps in order: start albendazole; CT with triple phase to map the cyst's relation to hepatic and portal veins and to exclude exophytic extension; MRCP because a mild itch and mildly raised alkaline phosphatase raise the possibility of a bile duct connection. At laparotomy the pericystic area is packed with hypertonic-saline mops, the cyst is aspirated, injected with 20 per cent saline, reaspirated, and the laminated membrane and daughter cysts removed; a bile-stained leak from the cyst floor is closed and the cavity drained — the bile duct is cleared on table or by post-operative ERCP if jaundice persists. Had this been a calcified, inactive, asymptomatic cyst, observation would be legitimate; had the patient been unfit for surgery with a WHO CE1-type cyst, PAIR would be the alternative.
How the exam frames it
FMGE stems typically hide the diagnosis in the occupation ("shepherd", "works in an abattoir", "pet dog in a rural household") rather than in the symptoms, and then test one of three forks: which organism (granulosus, not multilocularis, in India), which test confirms (imaging plus ELISA — not Casoni), and which complication changes the operation (cysto-biliary communication). The classic distractor pair is amoebic liver abscess versus hydatid cyst: the abscess is single, homogeneous, serology-negative for echinococcus and responds to metronidazole; the hydatid cyst has septations and daughter cysts. A second favourite asks what to do with spillage — the answer is anaphylaxis management first, then prolonged albendazole to prevent secondary echinococcosis.
Frequently asked questions
Which investigation is first-line for a suspected hydatid cyst of the liver?
Ultrasound of the abdomen is the first-line test, showing daughter cysts, septations or a detached membrane (water-lily sign); ELISA for hydatid antibody supports the diagnosis, and CT or MRCP maps anatomy before intervention.
What is PAIR and when is it preferred?
Puncture, aspiration, injection of a scolicidal agent and reaspiration, performed under albendazole cover for suitable uncomplicated cysts (WHO CE1-CE3) in patients who are unfit for or refuse surgery.
Why is formalin no longer used as a scolicidal agent?
Formalin entering a cysto-biliary communication causes sclerosing cholangitis; 20 per cent hypertonic saline or absolute alcohol is used instead.
How does a cysto-biliary communication present?
With jaundice, cholangitis or urticaria, bile-stained cyst aspiration at surgery, and it converts the operation into bile-duct exploration or definitive hepatic resection rather than simple cyst evacuation.
What is the dose of albendazole used with surgery?
Albendazole 15 mg/kg/day in two divided doses (commonly 400 mg twice daily in adults), started before the procedure and continued afterwards for one to six months depending on residue and spillage.