Alveolar echinococcosis of the liver in a Tokyo resident with an unknown route of infection: report of a case.

We report the case of a 45-year-old Tokyo man who developed alveolar echinococcosis of the liver, which is an extremely rare disorder in Japan, except for Hokkaido, Japan's northernmost island. The findings of multiple clustered cysts on computed tomography were unlike those of any hepatic tumors we had previously encountered. T2-weighted magnetic resonance imaging revealed the characteristic findings of small cysts with a very high signal intensity. The tumors were successfully removed by a hepatic resection. The patient lives in Tokyo, but has visited Hokkaido many times. The exact route of infection in this patient remains unclear. Sliced raw venison, which he reported eating on every visit to Sapporo in Hokkaido, represented the only potential route of infection we could identify. This meat may have somehow become contaminated with embryonated eggs. Nowadays, even city inhabitants are at risk of developing rare diseases due to the rapid development of transportation systems.