Dual-isotope subtraction scintigraphy and SPECT-CT for preoperative localization of parathyroid adenomas

Primary hyperparathyroidism (PHPT) is often caused by a parathyroid adenoma (PTA). Subtraction scintigraphy with ¹²³I and ^99mTc -MIBI SPECT-CT, and neck ultrasound examination as a hybrid scan (HS) can be used to localize the PTA in order to promote minimally invasive surgery.

This study evaluated patients referred for HS, the ability of the HS to correctly localize PTA(s), as well as the diagnostic performance of HS.

Data was retrospectively analyzed for 300 patients with PHPT referred for HS from 2019 to 2023 in a single-centre hospital. We used Begg and Greenes' correction method to calculate diagnostic accuracy, as well as calculated percentage of adenoma(s) correctly localized per patient who underwent PTX or bilateral neck exploration (BNE).

In 282 patients with PHPT undergoing HS for PTA localization, the HS was positive in 71%. Only 65% of these patients were referred to PTX. Using correction methods, we found a sensitivity and specificity of the HS of 73% and 78%, respectively. The positive predictive value was 99%, while the negative predictive value was 9%. The HS correctly localized PTA in 90% of the patients. Scintigraphy correctly localized 86% of the PTAs, SPECT-CT 85%, and ultrasound 76%.

A positive HS was very likely to localize the PTA correctly, whereas a negative HS had limited diagnostic value. Surprisingly, a large proportion of patients undergoing HS were never considered for surgery, resulting in partial reference bias in the evaluation of the diagnostic accuracy.