A hydatid cyst is a parasitic lesion caused by the larval stage of the tapeworm Echinococcus granulosus, transmitted to humans through accidental ingestion of eggs shed in the faeces of infected dogs. Once ingested the embryo penetrates the intestinal wall, enters the portal circulation and lodges most commonly in the liver (60–70%) followed by the lungs (20–30%). The cyst has a three-layered structure: an outer host-derived fibrous pericyst a middle ectocyst (laminated membrane) and an inner germinal layer producing brood capsules, protoscolices and daughter cysts. The disease is endemic in pastoral communities across the Middle East, Central Asia, Africa, South America and the Mediterranean.
Symptoms
Hydatid cysts grow slowly (1–5 cm/year) and may remain asymptomatic for years before producing symptoms. Hepatic cysts typically cause dull right upper quadrant discomfort, a sense of abdominal fullness and a palpable mass in the right hypochondrium. Biliary erosion produces obstructive jaundice and cholangitis. The most feared complication is spontaneous or traumatic rupture, releasing antigenic cyst contents into the peritoneal cavity and triggering a potentially life-threatening anaphylactic reaction. Secondary peritoneal seeding following rupture leads to widespread dissemination and recurrent disease. Superinfection of the cyst produces a hepatic abscess with fever, rigors and systemic sepsis.
Diagnosis
Abdominal Ultrasound is the first-line investigation, demonstrating the pathognomonic "water lily sign" a detached floating endocyst or visible daughter cysts and internal septations. The WHO-IWGE classification (CE1–CE5) stratifies cysts by activity and directly guides treatment decisions. CT scan provides precise anatomical detail, confirming cyst size, location, relationship to biliary structures and pericyst calcification indicating inactivity. Serology (ELISA, indirect haemagglutination assay) supports the diagnosis, though sensitivity is reduced in calcified or pulmonary cysts.
Treatment
PAIR (Puncture, Aspiration, Injection, Re-aspiration) is the preferred minimally invasive approach for uncomplicated accessible cysts involving ultrasound-guided aspiration, injection of a scolecidal agent to sterilise the cyst and re-aspiration of contents. Albendazole (400 mg twice daily) is started 7 days before PAIR and continued for at least 4 weeks to prevent secondary seeding. Surgery is the gold standard for large, complicated cysts, those with cystobiliary communication or those failing percutaneous management. The operative principle centres on sterilising the cyst before opening, evacuating the endocyst without spillage and managing the residual cavity by omentoplasty or drainage with meticulous closure of any biliary communications. Albendazole monotherapy alone is reserved for small uncomplicated cysts and as adjuvant therapy surrounding all interventions.