MEDULLARY CARCINOMA OF THE THYROID - ACCURACY OF DIAGNOSIS BY FINE-NEEDLE ASPIRATION CYTOLOGY

BACKGROUND. A preoperative diagnosis of medullary carcinoma of the thy roid (MCT) allows for the investigation of associated multiple endocri ne neoplasia/pheochromocytoma, and definitive surgery without the need for frozen section. Criteria for cytodiagnosis are well known but var iable patterns of presentation may cause diagnostic difficulty. METHOD S. This study examines the accuracy of cytodiagnosis and the value of ancillary tests in 17 patients seen between 1976 and 1997. Nine patien ts underwent thyroid gland aspirations, five patients underwent fine-n eedle aspiration (FNA) of the thyroid and cervical lymph nodes, and th ree patients underwent cervical lymph node aspiration alone. Electron microscopy (EM) of aspirated material was performed in nine cases and immunocytochemistry in two cases. RESULTS. In all cases the diagnosis was suggested by FNA. In four cases, diagnosis and management were bas ed on cytology alone. EM of FNA material was confirmatory in nine case s, two of which also showed positive calcitonin immunocytochemistry. I n three cases the diagnosis was not proven until surgical resection, a nd in one case FNA confirmed lymph node metastasis in known MCT. Froze n section in five patients did not change the level of diagnostic conf idence over the FNA diagnosis in any case. In four other thyroid tumor s (one Hurthle cell follicular carcinoma, two anaplastic carcinomas, a nd one hyperplastic nodule) MCT was suspected in the FNA differential diagnosis but later excluded. In the Hurthle cell tumor immunoperoxida se staining was positive for calcitonin and in one anaplastic carcinom a, a neuroendocrine phenotype was suggested. In the latter case, addit ional EM excluded MCT. CONCLUSIONS, Although correct diagnosis is made by cytology in the majority of instances, other tumors may show cytol ogic findings similar to MCT. EM of FNA material was found to be the m ost definitive method of proving or excluding MCT. Immunocytochemistry may be misleading for rarely performed tests. Cancer (Cancer Cytopath ol) 1998;84:295-802. (C) 1998 American Cancer Society.