(99m)Tc-MIBI Uptake in a Thyroid Adenoma with Diffuse Adipose Metaplasia

A 71-year-old female underwent a (99m)Tc-MIBI scan to characterize a cold nodule (30 mm) of the left thyroid lobe. The nodule showed diffuse uptake and retention of the radiotracer. After resection, histological examination demonstrated a microfollicular adenoma with diffuse white adipose metaplasia. Although mitochondria in brown adipose tissue have been widely studied, we have only a limited understanding of the relevance of mitochondria in white adipose tissue. Active mitochondria are present in white adipocytes, and this may account for the MIBI uptake, mimicking a hyperproliferation pattern, in our patient.