Granular Cell Tumor of the Thyroid

ABSTRACT

Granular cell tumor is not uncommon and is a well recognized entity which may arise at virtually any site of the body. However, occurrence in the thyroid is extremely rare and has not been described well. Only three cases could be found in the English literatures. We report a case of granular cell tumor of the thyroid in a 30 year-old woman. The tumor was illdefined, infiltrative and was composed of diffuse sheets of polygonal to fusiform cells with abundant eosinophilic granular cytoplasm. The tumor showed evidence of Schwann cell differentiation in immunohistochemical and ultrastructural examinations. Differentiation from more common thyroid tumors having oncocytic granular cytoplasm should be made by immunohistochemistry or electron microscopy.