A 33 year old woman presents with difficulty concentrating, muscle cramps, constipation, gastrointestinal upset / bloating, and irregular menses.
Serum TSH is at the upper end of the normal range (4.2 mIU/L) and thyroid ultrasound is requested. Transverse ultrasound images through the thyroid:
A nodule is noted at the posterior aspect of the right mid thyroid (arrowhead).
This hypoechoic nodule measures up to 1.4 cm and appears separate from the the thyroid.
Color Doppler evaluation of the nodule:
Doppler ultrasound images show ample peripheral vascularity associated with the nodule and a likely inferior feeding vessel (seen at the right aspect of the longitudinal images).
Further laboratory studies showed elevated calcium 10.9 mg/dL and elevated parathyroid hormone 118 pg/mL. These labs confirm primary hyperparathyroidism, and ultrasound images might be considered diagnostic for parathyroid adenoma.
In this case a Tc99m sestamibi parathyroid scan was performed for confirmation. Maximum intensity projection (MIP) from early acquisition (20 min after radiotracer injection):
MIP from delayed acquisition (2 hr after injection):
While the thyroid activity decreased in intensity from early to delayed image, there is a persistent intense focus of radiotracer uptake posterior to the right mid thyroid (right can be identified as the side opposite the heart). This is diagnostic of parathyroid adenoma.
Fused axial SPECT/CT images confirm radiotracer activity associated with a soft tissue nodule posterior to the right mid thyroid in the tracheoesophageal groove (arrowhead).
Parathyroid adenoma is a benign tumor causing enlargement of a parathyroid gland, and a single adenoma accounts for 80-90% of cases of primary hyperparathyroidism. The role of imaging is to identify the hyperfunctioning gland to assist in surgical planning, as the diagnosis is (usually) already known based on presentation and laboratory tests.
Parathyroid adenomas are very vascular tumors, resulting in peripheral color flow and often a feeding vessel on Doppler ultrasound. Similarly multiphase CT will show avid arterial phase enhancement, often with washout in delayed phase. Parathyroid adenomas (specifically oxyphil cells) also contain large numbers of mitochondria, resulting in persistent localization of Tc99m sestamibi. Adenomas typically washout slower than thyroid tissue, however up to 20-30% may not display this pattern. Thus close inspection of early phase SPECT/CT images for areas of focal uptake is important.
Johnson NA, et al. AJR 2007;188:1706-15. Lavely WC, et al. J Nucl Med 2007;48:1084-9. Ziessman HA, O’Malley JP, Thrall JH, eds. Nuclear Medicine, the Requisites, 4th ed. Philadelphia: Elsevier, 2014.