Three-dimensional cytomorphology in fine needle aspiration biopsy of medullary thyroid carcinoma

OBJECTIVE: To elucidate three-dimensional (3-D) cytomorphology in fine need le aspiration biopsy (FNAB) of medullary thyroid carcinoma (MTC). STUDY DESIGN: FNAB was performed on tumors from five patients with MTC. The aspirate was stained and observed under a light microscope (LM), The aspir ate was also fixed, dehydrated, critical point dried, spattered with gold i ons and observed with a scanning electron microscope (SEM). For transmissio n electron microscopy (TEM), the specimen was fixed, dehydrated, embedded i n an Epon mixture, cut with an ultramicrotome, mounted on copper grids, ele ctron doubly stained with uranium acetate and lead citrate, and observed wi th TEM. Findings tinder SEM were correlated with those tinder LM and TEM. RESULTS: Under SEM, 3-D cytomorphology of MTC displayed a disorganized cell ular arrangement with indistinct cell borders in three cases, The cell surf ace was uneven and had granular protrusions that corresponded to secretory granules observed tinder TEM, In one case with multiple endocrine neoplasia type IIB, there were abundant granules on the cell surface. In one case of sporadic MTC with multinucleated tumor giant cells and small cells, granul ar protrusions also were noted on the cell surface. CONCLUSION: Granular protrusion was a characteristic finding in FNAB of MTC under SEM and might be helpful in the differential diagnosis.