A Thyroid Nodular Hyperplasia with Adipose Metaplasia: A Case Report

초록

Thyroid nodular lesions with fat component are very rare. Very few cases were reported in the literature. A 48-year-old female patient was admitted into Inha University Hospital with an incidentally found neck mass. Ultrasound image showed an isoechoic solid nodule with hypoechoic rim at left lower portion of left thyroid. The nodule measured 2.4 × 1.5 × 3.7 cm. Ultrasound-guided fine needle aspiration was done. The lesion was diagnosed as atypical cells of undetermined significance on aspiration cytology. The smear revealed several small clusters of atypical follicular cells showing pale nuclei and irregular nuclear membrane in a background of blood and small amount of colloid. The patient underwent lobectomy of left thyroid. Microscopically, the nodule was confined to the thyroid parenchyma. The nodule revealed admixed benign thyroid follicles and mature adipose tissue. There was no evidence of malignancy, such as papillary carcinoma or follicular carcinoma. Also, we excluded the possibility of follicular adenoma because there was no definite capsule. The admixed adipose tissue did not have continuity with perithryoid soft tissue. The nodule was positive for CD56, but negative for galectin-3, cytokeratin 19, and cyclin D1. We diagnosed this lesion as nodular hyperplasia with adipose metaplasia. The pathogenesis of mature adipose tissue in thyroid nodule is unclear. It may originate from metaplasia of stromal fibroblast due to tissue hypoxia or entrapment of adipose tissue during embryogenesis.