Cancer in cystic lesions of the thyroid.

We reviewed the records of 341 patients who underwent thyroidectomy for the suspicion of cancer between 1975 and 1980. Cancer of the thyroid was found in 14% of them. Although cysts of the thyroid (pathologic finding of a fluid-filled cavity greater than 1 cm in diameter) were encountered in 35% of the patients, cysts were similarly distributed among patients with benign conditions (27%) or with cancer (33%). Most of the thyroid cysts in patients with carcinoma measured 2 to 4 cm in diameter. The cancer was found within the cystic cavity. The cysts in patients with cancer appeared to originate from necrosis of the tumor. B-mode ultrasonography was not reliable in differentiating cystic and solid lesions. The demonstration of the cystic nature of a thyroid nodule does not rule out the diagnosis of cancer of the gland.