Overly descended superior parathyroid adenoma: common cause of false localization in the parathyroid imaging.

Objectives: Tc-99m sestamibi parathyroid scan is a well-established method to localize a parathyroid lesion preoperatively in the patients with a hyperparathyroidism. We look at the causes of a false localization in this study; for example, an overly descended superior parathyroid adenoma (ODSPA) mimics as an inferior parathyroid adenoma in the 2-dimensional parathyroid imaging. MATERIALS AND

Methods: We identified 71 patients with primary hyperparathyroidism who had undergone parathyroidectomy. Dual- phase parathyroid imaging was obtained and SPECT study of neck and chest at 1 hour post injection. Images were evaluated by observing early and delayed planar images and MIP images as well as orthogonal reconstructed slices. The images were retrospectively evaluated and correlated with surgical findings to localize adenomas to 1 of 4 neck quadrants and lateralize them to the correct side. Accuracy of identifying multigland disease was also evaluated. RESULTS: There were 60 patients with a single adenoma, 6 patients with a double adenoma and 5 patients with multigland hyperplasia. 62/71 (87%) patients were correctly lateralized. Among the 60 patients with single adenoma, there were 7 patients who had ODSPA in which only 1 patient was correctly identified. Five patients with a single adenoma were erroneously identified having ODSPA, but none of them had it. One out of 5 patients with hyperplasia and 1 of 6 patients with double adenoma were correctly localized. CONCLUSIONS: The frequency of ODSPA is about 12% (7/60) in the patients presenting with single adenoma in our study. ODSPA is one of main causes of false localization in the parathyroid imaging. Understanding of parathyroid gland migration during the embryology and surgical anatomy is important to localize ODSPA correctly. Surgeons may miss these adenomas, which are always posterior to the coronal plane of the recurrent laryngeal nerve, if the dissection is not continued deep enough in a paraesophageal or retroesophageal plane.