Two-phase (low-dose) computed tomography is as effective as 4D-CT for identifying enlarged parathyroid glands

Background: Four-dimensional computed tomography (4D-CT) is often used for patients with primary hyperparathyroidism and non-definitive localization after Sestamibi scan (MIBI) and ultrasound (US), but may expose patients to unnecessary radiation, typically between 10 and 26 millisieverts (mSv). We hypothesize that a simpler two-phase CT protocol would have a similar sensitivity, specificity and accuracy to those published for 4D-CT, while exposing the patient to less radiation. Methods: We reviewed 54 patients with primary hyperparathyroidism and non-definitive localization studies who had a two-phase CT between 2009 and 2012 at our tertiary referral center. Results: The mean radiation dose of two-phase CT over the course of the study was 5.2mSv (range 3.5mSv-9.1mSv). Two-phase CT had a 77% (CI=65%-86%) sensitivity and an 87% (CI=73%-95%) specificity to lateralize enlarged parathyroid glands to the correct side of the neck and a 58% (CI=45%-68%) sensitivity and 91% (CI=83%-94%) specificity to localize parathyroid tumors to the correct quadrant of the neck. The overall accuracy of two-phase CT to lateralize enlarged parathyroids was 81% (CI=73%, 88%) and the accuracy to localize enlarged parathyroids was 79% (CI=73%, 84%). Discussion: As a second line investigation two-phase CT has a similar sensitivity, specificity and accuracy to those published for 4D-CT in patients with non-localized, enlarged parathyroids with less radiation exposure. Two-phase CT can help localize enlarged parathyroid glands not definitively identified using MIBI and US. Conclusion: Two-phase CT allows clinicians to accurately identify enlarged parathyroid glands while exposing the patient to less radiation than 4D-CT.