Humeral hydatid cyst complicated with extraosseous involvement: a case of unusual location of echinococcosis.

Hydatid disease is a parasitic disease most commonly caused by Echinococcus granulosus that seldom involves the skeleton and is still common in the countries of the temperate zones. We present an extremely rare case report of a young patient with humeral hydatid disease complicated with extraosseous involvement. Plain film of the left humerus demonstrated distortion of the axis, regional expansion of the humeral shaft with minimal thinning areas of the cortex. Additionally, numerous radiolucent areas of the humeral shaft were observed especially at the distal part of the bone. No calcification of the soft tissues was noticed. Computed tomography examination showed significant destruction of the trabecular bone of the humeral head and polycystic appearance of the bone marrow with regional calcifications into the lumen. Additionally, a large cystic lesion between medial and lateral head of the triceps muscle with some foci of calcifications were observed. Magnetic resonance imaging revealed the multiocular nature of the lesion into the humeral lumen with a cystic lesion involving the soft tissues of the upper arm. The cyst showed contrast enhancement at the pericyst capsule of the cyst after Gadolinium-DTPA administration.