Rhabdomyomas of the head and neck are exceptionally rare benign mesenchymal
tumors. Although histology is very characteristic, several differential diagnoses have to be considered. We investigated five patients with extracardiac
rhabdomyoma of the head and neck (median age 65.9 years), four of them presenting with adult
rhabdomyoma (AR) and one with fetal
rhabdomyoma (FR). We analyzed the histological findings, with special regard to separation from
hibernoma (two patients) and
granular cell tumor (GCT; six patients, median age 31 years). Both FR and AR showed polygonal eosinophilic cells with peripherally or centrally localized nuclei and cross striations, while in
hibernoma, multivacuolated cells with centrally localized nuclei were detected. In GCT, polygonal eosinophilic cells with granular
periodic-acid-Schiff-positive cytoplasm were found; in one case, atypical GCT with increased pleomorphism and mitotic rate was observed. Pseudoepitheliomatous
hyperplasia occurred both in FR and GCT. Immunohistochemically,
rhabdomyomas were strongly positive for myogenic markers (
desmin, actin, and
myoglobin) but negative for S-100, while
hibernoma and GCT strongly expressed S-100. Concerning the differential diagnosis of
rhabdomyoma, GCT has to be especially considered since this
tumor can undergo malignant transformation.