Question
Hydatid cyst
Answer
A hydatid cyst is the larval (metacestode) stage of Echinococcus granulosus, developing in the intermediate host (humans, sheep, cattle), most commonly lodging in the liver or lungs, developing slowly into a large, fluid-filled cyst.
Structure: pericyst (outer host-derived fibrous capsule); laminated (ectocyst) membrane (acellular, parasite-secreted); germinal (endocyst) layer (innermost, producing brood capsules with numerous protoscolices — “hydatid sand” — and sometimes daughter cysts).
Cyst fluid: clear, highly antigenic — cyst rupture can provoke severe anaphylactic reaction and secondary dissemination.
Diagnosis: imaging (ultrasound/CT/MRI) is the primary tool; serology (ELISA) supports diagnosis.
Treatment: surgical excision (avoiding spillage) with perioperative albendazole; PAIR technique for selected cysts.