Localized adiposity of the thyroid, clinically mimicking an adenoma.

A case of localized adiposity of the thyroid in a 35-year-old woman with a long history of steroid therapy for nephrotic syndrome is reported. A well-demarcated yellowish mass measuring 2 cm in diameter was found in the upper portion of the right lobe of the thyroid. Microscopically, this lesion was composed of mature adipose tissue partially mixed with thyroid tissue and had no distinct capsule. The nontumorous thyroid tissue showed features of Hashimoto's thyroiditis. At least two factors-hamartomatous malformation and metabolic disturbance-may be involved in the histogenesis of this localized adiposity.