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

Objective: 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.

Design: 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).

Results: Chest CT revealed a mediastinal mass measuring 5 cm in diameter abutting the right thyroid lobe.