Parathyroid 4D CT in Primary Hyperparathyroidism: Exploration of Size Measurements for Identifying Multigland Disease and Guiding Biochemically Successful Parathyroidectomy

BACKGROUND. In patients with primary hyperparathyroidism (PHPT), bilateral neck exploration is necessary for multigland disease (MGD), whereas minimally invasive parathyroidectomy is often preferred for single-gland disease (SGD). An existing system (the 4D-CT MGD score) for differentiating SGD from MGD with the use of preoperative parathyroid CT considers the size of only the largest candidate lesion. OBJECTIVE. The purpose of this study was to assess the utility of the size of the second-largest lesion on parathyroid CT for differentiating SGD from MGD as well as the utility of individual gland size for predicting the need for surgical removal and to derive optimal size thresholds for these purposes. METHODS. This retrospective study included patients with PHPT who underwent biochemically successful parathyroidectomy after preoperative parathyroid CT. Clinical radiology reports were reviewed to classify reported candidate parathyroid lesions as low-, intermediate-, or high-confidence lesions. Resected hypercellular parathyroid lesions were correlated with clinically reported candidate lesions. Patients were classified as having SGD or MGD on the basis of operative and pathology reports, independent of CT findings. One observer retrospectively determined the estimated volume (0.52 x length x width x height) and maximum diameter of clinically reported high-confidence lesions, as well as the 4D-CT MGD scores from the examinations. Diagnostic performance was assessed. RESULTS. The sample comprised 62 patients (41 women, 21 men; median age, 65 years), 47 of whom had SGD and 15 of whom had MGD, with 151 candidate lesions, including 106 high-confidence lesions. Based on the second-largest high-confidence lesions, an estimated volume threshold of 60 mml or greater achieved 53% sensitivity and 96% specificity, whereas a maximum diameter threshold of 7 mm or greater achieved 67% sensitivity and 96% specificity for MGD; a 4D-CT MGD score of 3 or greater achieved 47% sensitivity and 68% specificity for MGD. For predicting the need to remove a gland for successful parathyroidectomy, an estimated volume threshold of 114 mm(3) or greater achieved 84% sensitivity and 97% specificity, and a threshold of 55 mm(3) or greater achieved 93% sensitivity and 87% specificity; a maximum diameter threshold of 7 mm or greater achieved 93% sensitivity and 84% specificity. CONCLUSION. The estimated volume and maximum diameter of high-confidence candidate lesions can differentiate SGD from MGD and identify individual glands requiring removal for successful parathyroidectomy. Differentiating SGD from MGD may be aided by considering both the first- and second-largest high-confidence lesions.