Fig. 1.

A, Transverse view of left thyroid lobe obtained at time of ultrasound-guided FNA of a 4.9 × 2.3 × 3.4-cm complex cystic nodule of a 36-yr-old female. The central cystic portion of the complex nodule is seen, along with a posterior solid portion (arrow). FNA cytopathology demonstrated scant cellularity with few groups of follicular cells and blood, but overall, the specimen was inadequate. The patient underwent left hemithyroidectomy for compressive dysphagia; surgical pathology revealed a 2.9-cm, partially cystic MTC on a background of nodular hyperplasia. B, Surgical section low-power view, showing cystic medullary thyroid cancer with a fragment of hyperplastic normal thyroid (top) (hematoxylin and eosin). C, Higher power view. D, Calcitonin immunohistochemistry revealing dense homogeneous reactivity. The postoperative calcitonin was undetectable, and CEA was 2.6. RET-protooncogene testing was negative for exons 10, 11, and 13–16. Completion thyroidectomy was deferred, and serum calcitonin, CEA, and neck ultrasound have remained normal through 3-yr follow-up.