Ectopic mediastinal parathyroid adenoma (Tc-99m Sestamibi parathyroid scan)
Presentation
Decompensated heart failure with incidental hypercalcemia (3.02 ng/mL) and markedly raised serum parathyroid hormone (PTH) of 170 pmol/L. No sonographic evidence of parathyroid enlargement.
Patient Data
Early phase Tc-99m sestamibi scan shows physiological uptake in the salivary glands and thyroid gland with additional intense focal uptake in the anterior mediastinum.
The two-hour delayed image shows tracer retention in the adenoma and clearing of the tracer from the thyroid.
The SPECT-CT of the thorax shows a heterogenous well-defined soft tissue lesion in the upper anterior mediastinum.
Case Discussion
Histology confirmed parathyroid adenoma.
Primary hyperparathyroidism due to ectopic parathyroid adenoma is a diagnostic and management challenge. Ectopic parathyroid adenoma accounts for up to 6 to 16% of hyperparathyroidism cases and 6% of these are found in the mediastinum 1.
The suspected parathyroid adenoma was revealed in the anterior mediastinum on the Tc-99m sestamibi scintigraphy with accurate localization by single photon-emission computed tomography-computed tomography (SPECT-CT) scan. Nuclear medicine imaging with dual phase Tc-99m sestamibi parathyroid scan showed a focal increased tracer uptake seen in the right anterior mediastinal region in the early 30 minutes and delayed 2 hour imaging. On SPECT-CT this uptake was seen at the anterior aspect of a well-defined soft tissue mass at the perivascular and right upper paratracheal region with a central hypodensity. This mass measures approximately 3.1 x 2.4 x 2.3 cm (AP x W x CC). The intraoperative serum parathyroid hormone dropped by >50% from baseline after resection of the mediastinal parathyroid adenoma and this is a strong predictor of a successful parathyroidectomy.
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