[Oncocytic variant of medullary thyroid carcinoma: case report].

Oncocytic tumors of the endocrine system are a group of rare entities described in several organs, including the thyroid gland. Medullary carcinoma can seldom show the predominance of cells with oncocytic changes but the positive immunostaining for calcitonin should be helpful for the correct diagnosis. We describe the case of a 71 year-old female Caucasian patient, with a hard 5 cm thyroid nodule for 2 months. There was no significant cervical adenopathy. Thyroid hormone levels were normal. The US-Doppler examination showed a centrally vascularized nodule. Cytopathology analyses was suspicious for follicular neoplasm with predominance of oncocytic cells, and a hemithyroidectomy was performed. Frozen section examination confirmed a follicular neoplasm and the definitive histopathological and immunohistochemical analyses was conclusive for a medullary carcinoma, oncytic variant. A total thyroidectomy was then performed, followed by adjuvant 131Iodine therapy. After a 40-month follow-up the patient is alive with no evidence of disease. Medullary carcinoma should be considered in the differential diagnosis of unusual thyroid carcinomas with predominance of cells with oncocytic changes.