Tc-99m sestamibi parathyroid gland scintigraphy: added value of Tc-99m pertechnetate thyroid imaging for increasing interpretation confidence and avoiding additional testing.

PURPOSE: To evaluate the benefit of adding a pertechnetate parathyroid scan (dual-isotope imaging) in the interpretation of sestamibi dual-phase parathyroid scintigraphy.

MATERIAL AND METHODS: One hundred and sixteen dual Tc-99m sestamibi (MIBI) and Tc-99m pertechnetate subtraction parathyroid studies, performed between January 2000 and February 2006, were retrospectively reviewed. Dual-phase technetium sestamibi examinations were initially interpreted, with blinding to the technetium pertechnetate findings. Subsequently, technetium pertechnetate scan findings were added, and changes in interpretation were recorded.

RESULTS: By adding Tc-99m pertechnetate imaging, the interpretation of 17 scans (17/116=14.6%) was substantially altered. This included 5 scans (4%) that changed from negative to positive and 9 scans (8%) that changed from equivocal to positive, excluding ectopic tissue and directing minimally invasive surgery, without the need for further imaging, such as ultrasound, in 12% of cases. One examination changed from positive to negative. In addition, 2 scans changed from equivocal to negative, necessitating further preoperative imaging for the evaluation of additional pathology such as thyroid nodules and lymph nodes and the consideration of hyperplasia. Among the remaining 99 patients, Tc-99m pertechnetate scans may also have contributed to the diagnosis in the 66 positive Tc-99m MIBI scans by increasing confidence in the interpretation and obviating additional imaging. Ten cases remained equivocal.

CONCLUSION: By adding Tc-99m pertechnetate imaging, scan interpretation was changed in 14.6% of cases, and interpretation confidence was enhanced in all but 10 remaining equivocal cases. The addition of a dual-isotope subtraction also eliminated the need for additional testing, such as ultrasound, in 12% of our cases. Increased confidence in interpretation that comes with dual-isotope subtraction may come at the cost of slight lengthening of imaging time but likely simplifies preoperative localization and decreases intraoperative time for many patients with primary hyperparathyroidism.