Enhanced localization of posteriorly-descending superior parathyroid adenomas by SPECT

Objectives Tc99m SestaMIBI parathyroid scintigraphy is used for preoperative localization of parathyroid adenomas. The more accurate the localization, the shorter time of neck exploration by the surgeon. Most laboratories add SPECT, primarily to detect ectopic adenomas within the mediastinum. It was our observation, however, that SPECT facilitates the localization of eutopic superior parathyroid adenomas that appear to be inferior adenomas on routine planar neck images. However, SPECT of the neck would indicate that these particular adenomas were posteriorly located within the neck, and were therefore superior adenomas. These superior adenomas would descend inferiorly in utero, thereby becoming superior adenomas that migrated inferiorly. In such circumstances such an adenoma should be reported as a "superior parathyroid adenoma with inferior descent". This is more helpful to the surgeon during neck exploration. Our aim was to determine the frequency with which such a descening superior adenoma mimicked an inferior adenoma on planar images, but was accurately localized by SPECT.

Methods Over a 3-year interval, the results of all parathyroid scans interpreted as inferior adenoma were compared to the operative reports, if available. The frequency with which an inferiorly-descended superior parathyroid adenoma appeared as an inferior adenoma on planar images was then determined.

Results 43 scan results indicated an inferior parathyroid adenoma. Pathology and operative reports were available for 31 of these patients. Four of these were false-positives, i.e. what was interpreted as parathyroid adenoma was proven thyroid lesions. Of the 27 true-positive scans (correctly interpreted as parathyroid adenoma), 12 (44.4%) were superior adenomas with inferior descent, as suggested by SPECT.

Conclusions A superior parathyroid adenoma with inferior descent (1) is not an uncommon occurence and (2) can be accurately localized by SPECT.