Pulmonary echinococcosis.

Echinococcosis or hydatid disease is caused by larvae of the tapeworm Echinococcus. Four species are recognised and the vast majority of infestations in humans are caused by E. granulosus. E. granulosus causes cystic echinococcosis, which has a worldwide distribution. Humans are exposed less frequently to E. multilocularis, which causes alveolar echinococcosis. E. vogeli and E. oligarthrus are rare species and cause polycystic echinococcosis. In cystic echinococcosis, humans are an accidental host and are usually infected by handling an infected dog. The liver and lungs are the most frequently involved organs. Pulmonary disease appears to be more common in younger individuals. Although most patients are asymptomatic, some may occasionally expectorate the contents of the cyst or develop symptoms related to compression of the surrounding structures. Other symptoms of hydatid disease can result from the release of antigenic material and secondary immunological reactions that develop from cyst rupture. The cysts are characteristically seen as solitary or multiple circumscribed or oval masses on imaging. Detection of antibody directed against specific echinococcal antigens is found in only approximately half of patients with pulmonary cysts. Surgical excision of the cyst is the treatment of choice whenever feasible.