Medullary carcinoma of the thyroid glad: diagnostic cytopathological characteristics.

Sixty fine needle aspiration biopsy samples of the medullary carcinoma of the thyroid, 49 primary and 11 recurrent/metastatic, were reexamined in order to determine diagnostic features and value of auxiliary techniques. In the smears, tumor cells were present either as single cells or in loose cohesive groups; in about one third of cases, three-dimensional groups predominated. Cells were of different shapes round-to-oval, polyhedral and spindle. The aspirates contained one or all three cell types. Large mononucleated cells were present in 47/60 cases and, in addition, in 34 of these multinucleated cells with nuclei arrayed in semicircular rows were present. Plasmacytoid and dendritic cells, observed in 58/60 cases, appear to be an important diagnostic feature. Red cytoplasmic granules and amyloid deposits could serve as an additional diagnostic clue. Among the auxiliary techniques, the demonstration of calcitonin and CEA immunoreactive cells proved to be the most helpful.