Cytology of hyalinising trabecular adenoma-like variant of medullary thyroid carcinoma

Medullary thyroid carcinoma is a rare thyroid neoplasm that can be either sporadic or familial. It occurs in adults, presenting as a solitary cold nodule on thyroid scan. Most are solid, firm, and non-encapsulated, and occur in the mid portion or upper half of the thyroid gland, corresponding to areas with greater numbers of C cells. We present a case of a 36-year-old female with a swelling in the front of her neck for six years. Fine needle aspiration done elsewhere revealed spindle cells, suggestive of a 'spindle cell neoplasm'. The histopathology of the thyroidectomy specimen showed features of a hyalinizing trabecular adenoma-like variant of medullary carcinoma. Subsequently, we performed aspiration on the received specimen and studied the cytological findings. The cytological diagnosis of this variant requires identification of the dual spindle and ovoid cell population and the granular neuroendocrine chromatin.