Echinococcosis in an infection of humans caused by the larval stage of the tapeworm Echinococcus granulosus and, occasionally, by E. multilocularis or E. vogeli. E. multilocularis is found in Alpine, sub-Arctic, or Arctic regions, including Canada, the U.S., and central and northern Europe and Asia and causes multilocular alveolar lesions that are locally invasive. Like all echinococcal species, E. multilocularis has intermediate hosts (mice and other rodents) and definitive hosts (dogs). The cyst of E. multilocularis has several unique properties: (1) the larval form remains in the proliferative phase, (2) the hydatid cyst is always multilocular, and (3) the vesicles progressively invade surrounding host tissue by peripheral extension of processes from the germinal layer.

Differential diagnostic considerations for the sonographic appearance of this patient’s liver lesions include metastatic carcinoma (especially concerning given this patient’s prior history of breast carcinoma) and primary tumors of the liver. Percutaneous liver biopsy yielded a diagnosis of hepatic alveolar echinococcosis from E. multilocularis infection, rather than metastatic breast carcinoma. In cases of hepatic alveolar echinococcosis, the fox is usually the main host, and this patient confirmed exposure of her pet dogs to Swiss alpine foxes. Sonographic features typically include single or multiple echogenic lesions; necrotic, irregular lesions without well-defined walls; clusters of calcification within lesions, and dilated bile ducts.

Although a specific diagnosis can be made by examination of aspirated lesion contents, serodiagnostic tests are often preferred because aspiration may result in leakage of infected fluid, resulting in either dissemination of infection or anaphylactic reactions. Treatment options in decreasing order of preference include: (1) surgical resection in combination with perioperative antibiotic administration, (2) PAIR (Percutaneous Aspiration, Infusion of scolicidal agents, and Reaspiration) in combination with peri-procedural antibiotic administration, and (3) medical therapy alone, using albendazole for 3-6 months, which generally results in cure in approximately 30% of patients and improvement in another 50%. Response to treatment may be assessed by serial imaging studies.

Prevention is achieved by treating infected dogs with praziquantel, by denying dogs access to infected animals, by limiting the number of stray dogs, and by vaccinating sheep.