Granular cell tumor arising in myelinated peripheral nerves. Light and electron microscopy and immunoperoxidase study.

The histologic, immunohistochemical and ultrastructural characteristics of two granular cell tumors arising from the right recurrent laryngeal and left facial nerves are described. S-100 protein was detected both in the nuclei and cytoplasm of the granular cells using the peroxidase-anti-peroxidase method. The ultrastructural findings in both cases support a Schwann cell derivation of the granular cells. It is suggested that the granularity of cells of granular cell tumor may represent a lysosomal disorder affecting most frequently neoplastic and nonneoplastic Schwann cells and occasionally other cells.