Granular cell variant of neurofibromatosis: ultrastructure of benign and malignant tumors.

A case of neurofibromatosis with a metastasizing malignant tumor is presented. The benign lesions were identified by light microscopy as neurofibromas containing granular cells typical of granular cell tumors. The malignant tumor was classified as a malignant granular cell tumor. Ultrastructural studies demonstrated common histogenetic and subcellular features of the benign and malignant tissues. The case is the first reported in which granular cells are seen in the lesions. The typical granular cell morphologic features of the malignant lesion support the concept of Schwann cell derivation of this group of tumors.