A spectrum of cytomorphologic variations in medullary thyroid carcinoma. Fine-needle aspiration findings in 19 cases

Medullary thyroid carcinoma (MTC), a rare malignancy with a variety of morphologic appearances, can mimic both primary and metastatic lesions of the thyroid gland and give rise to diagnostic problems when these tumors are aspirated. Although cytopathologic features of MTC have been well described, this study was undertaken to define and elaborate further, subtle morphologic variations, the recognition of which would be helpful in the diagnosis of MTC.

A retrospective review of 19 cases of histologically confirmed MTC was conducted. Fine-needle aspirations were performed by endocrinologists or cytopathologists using a 23- or 25-gauge needle. Smears were stained with Diff-Quik, Papanicolaou, or hematoxylin and eosin (H&E) stain. Cell blocks were routinely prepared, and 4-micron sections were stained with H&E.

Certain cytologic features, such as eccentric nuclei, neuroendocrinelike nuclei, inconspicuous nucleoli, binucleation and multinucleation, ill-defined cytoplasmic borders, and a clean background, were present in all cases. Additional helpful features seen in some but not in all cases included syncytial groups of cells, round to oval and spindle shapes, dendritic cell processes, the presence of amyloid, and nuclear molding and grooves.

The authors found that MTC could be adequately diagnosed by fine-needle aspiration, despite the frequent cytomorphologic variations, based on a set of features consistently present in all the cases included in this study. Features such as neuroendocrinelike chromatin and nuclear molding have not been previously described.