Radiograph and CT study in a 12-year old boy after trauma with the incidental finding of a ruptured echinococcal cyst. An intrapulmonary cyst with several membranes can be seen. The air-fluid level indicates a rupture of the ectocyst, with the endocyst collapsed and the membrane floating on the fluid (water lily sign).
The eggs enter the intestines via ingestion. There, the larvae develop and migrate through the intestinal wall to other organs via the bloodstream; the liver and lungs are most frequently affected. Here, cysts are formed containing immature worms. The further development cycle with the development of adult worms can only take place in the definitive host.