Teaching Case

A CT examination was performed and revealed multiple cystic lesions ranging in size from 2cm to 6cm. Some were simple and others were multicystic, involving the soft tissues of the right gluteal region, the posterior and anterior femoral region and the upper third of the calf (Figs 1 and 2).Diagnosis was soft tissue echinococcosis. At surgery, part of the mass was excised and pathological examination confirmed the diagnosis.

The clinical manifestation of hydatid disease in soft tissues is a palpable mass, either painless or painful. Most frequently patients with musculoskeletal involvement do not present hepatic or lung infestation. CT and US have been used for the evaluation of hydatidosis. Several patterns of the disease have been recognised: the unilocular cyst, the multivesicular lesion and the atypical or solid lesion. The patient in this case presented with a multivesicular lesion, which is characteristic of hydatid disease.

In musculoskeletal lesions the endovesicular daughter cysts and calcifications typical of hepatic lesions are not usually observed, so their absence does not exclude the diagnosis of cystic echinococcosis. This can be explained by the pathophysiology of the disease. All hydatid lesions start as purely cystic type I structures and if they develop daughter cysts or matrix (or both) they are termed type II cysts. When formed elements completely replace the nourishing fluid the type II lesion starves, dies and eventually becomes a calcified and biologically inert type III lesion. Musculoskeletal involvement is detected early so type I and type II lesions are most common.