Paediatric Imaging

Hydatid disease

infection with the tapeworm Echinococcus granulosus or E. Alveolaris which is rarer. Human infection is acquired usually by ingestion of contaminated water containing ova or by direct contact with infected animals. The ova, once ingested, burrow through the intestinal mucosa and reach the liver by the portal vein where they mature. The infection can affect any system in the body but most commonly the lung, brain, liver and musculoskeletal system. The cysts vary in size from about 1 cm to 10 cms.

An unruptured cyst has smooth outlines on chest radiographs. If it ruptures there is a cavity containing the ecocyst. Rupture of the echocyst usually causes a smooth-walled cavity, with the ruptured collapsed cyst in its base, the water lily sign. In the liver the cyst is usually large, may have wall calcification and contain daughter cysts. Rupture of a hydatid cyst into the biliary tree causes cholangitis. The cyst is seen as a fluid filled mass both on CT and ultrasound. In bone the radiographic appearance is that of an expansile osteolytic lesion. Cortical rupture is associated with soft tissue swelling which may calcify. Rupture into the spinal canal may cause cord compression. In the brain, the cysts are large, rounded and sharply defined, contain daughter cysts and compress surrounding brain. There is enlargement of or calcification of the wall when there is death of the primary cyst. See echinococcosis, hydatid disease and hydatid disease pulmonary involvement

HC