Is fine needle aspiration cytology a useful diagnostic tool for granular cell tumors? A cytohistological review with emphasis on pitfalls

BACKGROUND: Granular cell tumors (GCT) formerly known as Abrikossoff tumor or granular cell myoblastoma, are rare neoplasms encountered in the fine needle aspiration (FNA) service. Named because of their highly granular cytoplasm which is invariably positive for the S-100 antibody, the classic GCT is thought to be of neural origin. The cytomorphological features range from highly cellular to scanty cellular smears with dispersed polygonal tumor cells. The cells have abundant eosinophilic granular cytoplasm, eccentric round to oval vesicular nuclei with small inconspicuous nucleoli. The fragility of the cells can result in many stripped nuclei in a granular background. The differential diagnosis occasionally can range from a benign or reactive process to features that are suspicious for malignancy. Some of the concerning cytologic features include necrosis, mitoses and nuclear pleomorphism. METHODS: We identified 6 cases of suspected GCT on cytology within the last 10 years and compared them to their final histologic diagnoses. RESULTS: Four had histologic correlation of GCT including one case that was suspicious for GCT on cytology and called atypical with features concerning for a malignant neoplasm. Of the other two cases where GCT was suspected, one showed breast tissue with fibrocystic changes, and the other was a Hurthle cell adenoma of the thyroid. CONCLUSIONS: These results imply that FNA has utility in the diagnosis of GCT, and should be included in the differential diagnoses when cells with abundant granular cytoplasm are seen on cytology. Careful attention to cytologic atypia, signs of reactive changes, use of immunohistochemistry, and clinical correlation are helpful in arriving at a definite diagnosis on FNA cytology.