Unusual site of an embryonal rhabdomyosarcoma of the mesenchymal hepatic pedicle

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of children. Tumors arising in the extrahepatic biliary tree are extremely rare (less than 1% of cases). In this location, most are RMS of the botryoid type. We report a case of a 10-year-old child with embryonal RMS arising in the mesenchyma of the hepatic pedicle. Most tumor cells were large, round with abundant 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.