Rare presentation of occult medullary carcinoma of the thyroid as a mediastinal mass

To describe a rare case of occult (<1 cm in diameter) medullary thyroid carcinoma (MTC) in a 45-year-old woman, presenting as an asymptomatic mediastinal mass.

The diagnostic methodology included laboratory measurements of relevant biochemical and hormonal parameters including calcitonin (CT), carcinoembryonic antigen (CEA) and chromogranin A, and imaging techniques including ultrasound (U/S), computed tomography (C/T), magnetic resonance imaging (MRI) and radio labeled somatostatin analog ((111)In-DTPA-octreotide).

Chest CT revealed a mediastinal mass measuring 5 cm in diameter abutting the right thyroid lobe. CEA was elevated and an association with thyroid malignancies was considered. CT was found to be markedly elevated, pointing to the diagnosis of MTC metastatic to the mediastinum. The patient underwent total thyroidectomy, lymph node dissection and removal of the mediastinal mass. Histological examination revealed MTC of the right thyroid lobe measuring 0.5 cm, metastatic to regional and superior mediastinal lymph nodes.

Occult MTC can infrequently present as an asymptomatic mediastinal mass. Elevated serum CT and CEA along with imaging techniques leads to the correct diagnosis and surgical management of the disease.