Clinical implications of the rare thyroid carcinoma which is indistinguishable from a follicular adenoma

The inadequacy of the standard pathologic criteria for identifying certain well-differentiated thyroid follicular carcinomas from follicular adenomas in rare instances is illustrated by four cases. The excised thyroid nodule in these patients appeared to be adenoma, but subsequent local spread in the neck or distant metastases disclosed the actual malignant nature of the lesions. This observation is not intended as a basis for more extensive operations for adenoma, but rather as an indication for close, long-term observation. Postoperative, lifelong suppressive therapy with thyroid hormone is suggested for all patients with a diagnosis of follicular adenoma.