A case of ectopic para-tracheal parathyroid adenoma identified with whole-body 99mTc-sestamibi scan

Ectopic parathyroid glands are not rare. They are usually located between the mandible and mediastinum, and usually localized with standard imaging modalities (99mTc-sestamibi subtraction scintigraphy and 4D-CT). We report the case of a 67-year-old woman with severe hypercalcemia due to symptomatic primary hyperparathyroidism whose preoperative 99mTc-sestamibi and 4D-CT scans were non-localizing. During 4-gland exploration, one hypercellular parathyroid was excised, two normocellular parathyroids were biopsied, and bilateral low internal jugular vein sampling showed similar parathyroid hormone (PTH) levels. Despite treatment with zolendronic acid and cinacalcet, symptomatic PHPT persisted. A99mTc-sestamibi study using a modified anterior and posterior whole-body scintigraphy protocol with SPECT/CT revealed mild focal uptake in the right para-tracheal area, correlating with a mass on SPECT/CT. Sestamibi uptake was visually more conspicuous on posterior projection whole-body image. Thoracoscopic resection of this mass revealed a parathyroid gland (2.6 × 1.5 × 0.7 cm) composed almost entirely of chief cells. The lack of identifiable oxyphil content could explain the lack of or limited radiotracer uptake. The modified protocol differed from standard parathyroid imaging in the timing of radiotracer administration, timing of image capture, and types of images obtained could account for the eventual visualization of the ectopic tissue, and may be considered in challenging cases of suspected ectopic parathyroid gland.