A Simple Formula to Estimate Parathyroid Weight on 4D-CT, Predict Pathologic Weight, and Diagnose Parathyroid Adenoma in Patients with Primary Hyperparathyroidism
Randy Yeh, Y.-K.D. Tay, Laurent Dercle, Leonardo Bandeira, Maansi Parekh, John P. Bilezikian
Abstract
<h3>BACKGROUND AND PURPOSE:</h3> Parathyroid gland weight is a clinically relevant parameter used to diagnose parathyroid adenomas intraoperatively. We evaluated the accuracy of a formula to estimate parathyroid weight on preoperative 4D-CT. <h3>MATERIALS AND METHODS:</h3> A single-institution retrospective study was performed in patients with primary hyperparathyroidism who underwent 4D-CT between January 2013 and December 2014 with subsequent parathyroidectomy and surgical cure. All patients had correct localization of a solitary parathyroid adenoma. The longest 3 dimensions of all identified parathyroid glands were measured on CT, and weight was estimated using the formula: weight<sub>4D-CT</sub> (mg) = 1 mg/mm<sup>3</sup> × Length (mm) × Width (mm) × Height (mm) × π/6. We correlated weight<sub>4D-CT</sub> with pathology specimen weight (weight<sub>pathology</sub>). Using receiver operating characteristic analysis, we estimated the performance of weight<sub>4D-CT</sub> to discriminate a parathyroid adenoma from normal glands on 4D-CT and determined the optimal threshold based on the Youden index. <h3>RESULTS:</h3> One hundred sixteen patients (85 women, 31 men) were evaluated. Weight<sub>4D-CT</sub> was shown to be strongly correlated with weight<sub>pathology</sub> as demonstrated by Spearman ρ = 0.73 (<i>P</i> < .01), concordance correlation coefficient = 0.92 (95% CI, 0.89–0.94), and Cronbach α = 0.96. The performance of weight<sub>4D-CT</sub> for the diagnosis of parathyroid adenoma was excellent, with an area under the curve of 0.955 (95% CI, 0.925–0.985; <i>P</i> < .001). Based on the Youden index, the optimal threshold was >50 mg, with a sensitivity of 96.7% and a specificity of 95.7%. <h3>CONCLUSIONS:</h3> Radiologists can accurately estimate parathyroid adenoma weight on 4D-CT. This metric is highly correlated with pathologic weight, and a threshold cutoff of >50 mg can be used to distinguish parathyroid adenoma from normal glands.