Is Brown Adipose Tissue Visualization Reliable on (99m)Tc-Methoxyisobutylisonitrile Diagnostic SPECT Scintigraphy?

The (99m)Tc-MIBI has been used with great value as a diagnostic technique in patients with primary hyperparathyroidism. False-positive scans may occur due to misinterpretation of the physiologic distribution of the (99m)Tc-MIBI. Reviewing consecutive SPECT scans, we evaluated this possibility and assessed how frequently brown adipose tissue (BAT) is seen on (99m)Tc-MIBI scintigraphy. Here, we retrospectively reviewed scans of consecutive patients who were evaluated for parathyroid adenomas from March 2015 to June 2015, using dual-phase (early and delayed) planar imaging and SPECT. We identified 60 patients (48 female and 12 male; mean age, 52.25 ± 15.20 years; range, 22–86 years). We detected the presence of (99m)Tc-MIBI uptake in BAT in 20 of 60 patients (33.33%) in the neck. Although the patients with (99m)Tc-MIBI uptake in BAT were younger (mean age, 48.85 ± 15.27 years, range, 26–73 years) than the patients with no (99m)Tc-MIBI uptake (mean age, 53.95 ± 15.07 years, range, 22–86 years), this difference was not statistically significant (P = 0.224). The percentage of female patients with BAT detection was higher (17/48 patients; 37.5%) than that of the male population (3/12 patients; 25%), this difference was not also statistically significant (P = 0.85). In patient population referred to (99m)Tc MIBI scintigraphy of the parathyroid glands, uptake of (99m)Tc-MIBI in BAT should not be misinterpreted with (99m)Tc-MIBI-avid-tumors. Fused SPECT/CT images (not SPECT-only) are necessary to distinguish BAT from bone, muscle, thyroid, myocardium, parathyroids, and other structures in the neck and chest.