Embryonal rhabdomyosarcoma of the mesenchymal hepatic pedicle: an unusual site of origin

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of children. Tumors arising in the extrahepatic biliary tree are extremely rare (less th an 1 % of cases). In this location, most are RMS of the botryoid type. We r eport a case of a 10-year-old child with embryonal RMS arising in the mesen chyma of the hepatic pedicle. Most tumor cells were large, round with abund ant eosinophilic cytoplasm. A few cells were small round or spindle-shaped Tumor cells showed positive immunostaining for muscle markers : desmin and sarcomeric actin. Electron microscopy revealed 2 types of cells: some were undifferentiated and others showed striated muscle differentiation features .