Medullary carcinoma of the thyroid: a cytological, immunocytochemical, and ultrastructural study.

The cytomorphological features of 38 cases of medullary carcinoma of the thyroid on FNAC were studied. These cases were retrieved from the files of the cytopathology laboratory. In addition, staining for calcitonin (19 cases), thyroglobulin (5 cases), neurone specific enolase (7 cases), and carcinoembryonic antigen (8 cases) was done. Electron microscopy was done in two cases. On morphology, the presence of amyloid together with cytoplasmic granules was found to be diagnostic. The plasmacytoid cell type and the mixed cell populations were most commonly observed. Pseudononuclear inclusions were seen in 58% of cases. Calcitonin was present in 74% of cases. NSE was noncontributory, whereas CEA was positive in one of the calcitonin negative cases.