Planar parathyroid localization scintigraphy: a comparison of subtraction and 1-, 2- and 3-h washout protocols.

Introduction: With the advent of minimally invasive surgery to treat hyperparathyroidism, preoperative imaging of parathyroid glands has become routine practice. Scintigraphy and ultrasound are the two most common imaging techniques. Despite this, published sensitivities for scintigraphy vary enormously, and there is a multitude of protocols performed. This investigation compares the accuracies of planar subtraction and multiple washout images in the same group of patients.

Methods: We followed up 190 consecutive patients who underwent a combined subtraction and washout scintigraphy protocol and compared the results against surgical outcomes, taken as the gold standard. Technetium-99m sestamibi images were acquired at 5 min and at 1, 2 and 3 h, followed by a technetium-99m pertechnetate image for subtraction. Sixty-four of these patients also underwent ultrasound imaging for localization. The relative value of each part of the protocol in localizing adenomas was compared.

Results: The overall accuracy of this combined protocol for correct localization of both the side and axial level of parathyroid adenomas was 81% (90% when considering the side of the adenoma alone). Of all the nuclear medicine images produced, subtraction was the most useful. The 1 and 2 h washout images were comparable but the 3 h image added no value. The accuracy of ultrasound imaging was 55% for the side and pole and 60% for the side of the adenoma.

Conclusion: For optimal accuracy a planar parathyroid localization protocol should include subtraction and at least one washout image between 1 and 2 h after injection.