Appearance of Descended Superior Parathyroid Adenoma on SPECT Parathyroid Imaging

An ectopic superior parathyroid adenoma (SPA) descends inferoposteriorly and can migrate to the posterior mediastinum. It often appears on sestamibi planar parathyroid imaging as an inferior lesion, which can be misleading to inexperienced surgeons. Its correct identification before surgery will be of great help for correct surgical planning. We assessed the appearance of descended SPA on SPECT imaging. METHODS:Sestamibi SPECT imaging studies performed on 103 patients who had parathyroid adenomas with their origin and locations confirmed by surgery and histology were retrospectively reviewed. Abnormal foci seen on the SPECT images were grouped as to location relative to the thyroid gland as superior (S), middle (M), and inferior (I). The proximity between the focus and the thyroid on the sagittal SPECT images was graded from 0 to 2 with 2 being widely separated. RESULTS:Of the 103 SPECT studies, 89 were positive. Eleven of the 89 visualized foci were at the S levelall were SPA. Ten foci were at the M level, including 6 SPA and 4 inferior parathyroid adenomas (IPA). There were 68 foci at the I level; none (0%) of 56 in the I0 location, 2 (25%) of 8 foci in the I1 location, and all (100%) of 4 abnormal foci in the I2 location were descended SPAs. CONCLUSION:The more posteriorly located the abnormal focus, the higher the probability of descended SPA. Recognition of the characteristic appearance of descended SPA on SPECT imaging can have a significant impact on the surgical approach and prevent failed neck exploration.