Fine needle aspiration cytology of unsuspected metastatic hurthle cell carcinoma of the thyroid and its pitfalls: a report of two cases.

We discuss two cases of unsuspected metastatic thyroid carcinoma of Hurthle cell type, presenting as subcutaneous masses in the occipital scalp and supra-acetabular region of the right ilium; clinically suspected to be a lipoma and a vascular tumour, respectively. These two cases were initially investigated by fine-needle aspiration cytology. In case 1, a definitive diagnosis of metastatic Hurthle cell carcinoma was made based on cell block preparation and positive immunohistochemical stains for thyroglobulin and thyroid transcription factor-1. Case 2 was reported as suggesting an oncocytic process, metastatic Hurthle cell lesion. The filter preparations from both cases showed compact sheets and individual large polygonal cells with voluminous granular cytoplasm, eccentric nuclei with minimal atypia and bland chromatin. Scattered haemosiderin-laden macrophages and cystic debris were also identified in both cases. These cases are of interest as the bland cytologic features may lead to an erroneous benign diagnosis. Immunohistochemistry aids the definitive diagnosis of metastatic Hurthle cell carcinoma of thyroid especially when the presence of a previous thyroid lesion is not communicated to the laboratory.