Medullary thyroid carcinoma

Abstract

Medullary thyroid carcinoma (MTC) comprises approximately 1–2% of thyroid malignancies and occurs in sporadic and heritable forms. Hereditary forms include multiple endocrine neoplasia (MEN) type 2A, familial medullary thyroid carcinoma (FMTC), and MEN type 2B. Most cases of MTC demonstrate characteristic cytomorphology and a distinctive immunophenotype, but MTC can show a wide variety of cell shapes, nuclear and cytoplasmic features, and growth patterns. This morphologic heterogeneity leads to significant diagnostic challenges in the histologic and cytologic evaluation of this neoplasm. Characteristic features include a dispersed, noncohesive cell pattern, plasmacytoid and/or spindled cell shapes, finely granular chromatin, inconspicuous nucleoli, intranuclear pseudoinclusions, cytoplasmic granularity, and amyloid. Immunocytochemistry is helpful for distinguishing MTC from its cytologic mimics. Additional ancillary tests include measurement of calcitonin levels in needle washout fluid from FNA of thyroid nodules, thyroidectomy beds, and/or lymph nodes, particularly in patients with elevated serum calcitonin levels and/or with FNA findings that are inconclusive for MTC. Surgical treatment is usually total thyroidectomy and central lymph node dissection, with consideration of lateral cervical lymph node dissection depending on imaging studies and serum calcitonin levels.