Primary Hyperparathyroidism: Defining the Appropriate Preoperative Imaging Algorithm

Algorithm for imaging investigations in primary hyperparathyroidism. See also Table 1 for suggested activities and acquisition protocol. *Dual-tracer subtraction scan can be positive in patients with previous negative dual-phase imaging results. ^†Suggestive lesion seen only on nuclear imaging in area not accessible to US should not be considered discordant or inconclusive. ^‡Contrast-enhanced arterial-phase CT acquisition can be added (it can improve PPV of PET/CT in difficult cases). ^§To be considered only in repeat surgery cases with negative first-line and second-line imaging results.

Simultaneous dual-tracer ^99mTc-sestamibi and ¹²³I scan in 39-y-old patient with PHPT. (A) Parallel-hole collimator images with ⁹⁹Tc-sestamibi, ¹²³I, and subtraction. Parallel-hole subtraction image shows residual focus on right side of neck, barely visible focus on left side (arrow), and no ectopic foci. (B) Pinhole images over thyroid area with ⁹⁹Tc-sestamibi, ¹²³I, and subtraction. Pinhole subtraction image clearly shows 2 residual foci. Surgery confirmed diagnosis of double adenomas, and calcium level at 6 mo was normal. This example shows better resolution offered by pinhole images and reveals importance of computer subtraction, as visual comparison alone could have missed left-side focus. Computer subtraction should be well balanced, avoiding oversubtraction.

Simultaneous dual-tracer ^99mTc-sestamibi and ¹²³I scan in 62-y-old patient with PHPT. (A) Pinhole images of thyroid area with ^99mTc-sestamibi, ¹²³I, and subtraction. Pinhole subtraction image clearly identifies 2 residual foci: 1 at inner part of lower third of right thyroid lobe (arrow) and other at lower pole of left thyroid lobe (double arrow). (B) Axial SPECT/CT fusion images with ^99mTc-sestamibi (right) and ¹²³I (left), obtained at 2 different levels. On SPECT/CT axial views, right parathyroid lesion is located posteriorly, in paraesophageal position (arrow). This location is typical of prolapsed superior parathyroid gland (minor ectopia). Left inferior parathyroid lesion (double arrow) is located below lower pole of left thyroid lobe. Calcium level 6 mo after resection of 2 adenomas was normal.

84-y-old patient with PHPT and history of total thyroidectomy. Neck ultrasound results were negative. Simultaneous dual-tracer ^99mTc-sestamibi and ¹²³I parathyroid scan was performed after patient was instructed to withhold thyroid hormone therapy for 2 wk. (A) Pinhole images of neck show two ^99mTc-sestamibi–avid foci (1 on each side of neck), but ¹²³I scan clearly shows that focus on left side corresponds to thyroid remnant (arrow). (B) ^99mTc-sestamibi and ¹²³I SPECT/CT axial views without subtraction reveal posteriorly seated right parathyroid lesion and left thyroid remnant. Targeted surgery could be performed with resection of 600-mg right parathyroid adenoma.

¹⁸F-fluorocholine PET/CT performed 35 min after intravenous injection of ¹⁸F-fluorocholine in 71-y-old patient with PHPT. Results of neck ultrasonography and dual-phase ^99mTc-sestamibi parathyroid scan performed at another institution before referral were negative. ¹⁸F-fluorocholine PET (A) with maximum-intensity-projection and axial view images show ¹⁸F-fluorocholine–avid focus corresponding on axial PET/CT fusion and CT images (B) to small tissue lesion behind right sternoclavicular junction (arrows). Parathyroid adenoma (500 mg) was resected.