Occult medullary carcinoma of thyroid: an unusual clinical and pathologic presentation.

High calcitonin levels noted on a totally healthy 49-year-old man participating in a calcitonin control project led to a presumptive diagnosis of medullary carcinoma. Complete thyroid studies augmented by selective catheterization and quantitative calcitonin studies confirmed the clinical impression of medullary carcinoma. Surgery was recommended and a total thyroidectomy was performed. On gross examination no nodules or tumefactions were palpable. Histopathology showed diffuse C-cell hyperplasia in the midst of which a C-cell tumor and micromedullary carcinoma of the thyroid were found. Morphologically the full spectrum of changes from focal C-cell hyperplasia through the stages of diffuse and nodular hyperplasia to the final development of medullary carcinoma are demonstrated by light and electron microscopy. The patient's postoperative course was benign and for the subsequent three years he had continued asymptomatic with normal calcitonin levels.