Role of single photon emission computed tomography/computed tomography in localization of ectopic parathyroid adenoma: a pictorial case series and review of the current literature.

The parathyroid glands are located posterior to the upper and lower poles of the thyroid and are derived from the third and fourth pharyngeal pouches. Usually there are only 2 superior glands, whereas only 40% of patients have their inferior glands located near the inferior thyroid poles. Ectopic locations include the carotid sheath, anterior mediastinum, retropharynx, or intrathyroidal locations. Single photon emission computed tomography/computed tomography (SPECT/CT) offers the advantage of combining function and anatomy for exact localization of ectopic parathyroid adenomas. In this pictorial review, we present 4 cases of hyperparathyroidism caused by ectopic parathyroid adenomas and review the literature on the additional value of their localization with SPECT/CT. Combined SPECT/CT scanners permit more reliable localization of ectopic adenomas. The additional information can aid in exact preoperative localization. In one study of 16 patients, SPECT/CT identified 39% more lesions compared with SPECT imaging alone. In other comparisons of planar, SPECT and SPECT/CT imaging modalities, SPECT/CT permitted the highest reader confidence in localization, especially for mediastinal adenomas. Larger studies are needed to establish the role and cost-effectiveness of SPECT/CT.