Adult cervical thymus revealed by thyroid medullary carcinoma.

A 64-year-old man presented with elevated thyrocalcitonin, and a history of resected thyroid medullary carcinoma. Cervical thymus was detected incidentally in the neck dissection resection specimen for thyroid medullary carcinoma extension. This case was peculiar due to the presence of a thymic microcyst and the coexistence of parathyroid tissue along with the thymic lobules. Persistent hypocalcaemia, requiring calcium intake, occurred after resection. Although rare, the presence of such neck branchial arch abnormalities should be considered for a successful management of extensive malignant thyroid tumours.