CLEAR-CELL RHABDOMYOSARCOMA

A clear cell rhabdomyosarcoma was studied by light microscopy, histoch emistry immunohistochemistry, and electron microscopy. It was a large, painful left parapharyngeal mass in a 10-year-old boy with intracrani al extension and cervical metastatic enlarged lymph nodes. Tumor tissu e was macroscopically grayish. At microscopic examination, the archite cture was diffuse and focally alveolar. Tumor cells were of three type s. Most cells were large, round or polygonal, with abundant clear vacu olated cytoplasm. Fibrils were sometimes found to be present around th e nucleus. Nuclei often had irregular outlines and multiple nucleoli. Mitotic activity was high. Some round or elongated cells had eosinophi lic fibrillar cytoplasm and were found to have a few double striations . A few cells were round and medium sized with a high nucleocytoplasmi c ratio. Periodic acid-Schiff stain demonstrated huge amounts of intra cytoplasmic glycogen in clear cells. Tumor cells showed positive immun ostaining for muscle markers (desmin, muscle actins, dystrophin). Elec tron microscopy showed large lakes of glycogen, lipid droplets, and st riated muscle features.