A Simple Formula to Estimate Parathyroid Weight on 4D-CT, Predict Pathologic Weight, and Diagnose Parathyroid Adenoma...

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.

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_4D-CT (mg) = 1 mg/mm³ × Length (mm) × Width (mm) × Height (mm) × π/6. We correlated weight_4D-CT with pathology specimen weight (weight_pathology). Using receiver operating characteristic analysis, we estimated the performance of weight_4D-CT to discriminate a parathyroid adenoma from normal glands on 4D-CT and determined the optimal threshold based on the Youden index.

One hundred sixteen patients (85 women, 31 men) were evaluated. Weight_4D-CT was shown to be strongly correlated with weight_pathology as demonstrated by Spearman ρ = 0.73 (P < .01), concordance correlation coefficient = 0.92 (95% CI, 0.89-0.94), and Cronbach α = 0.96. The performance of weight_4D-CT for the diagnosis of parathyroid adenoma was excellent, with an area under the curve of 0.955 (95% CI, 0.925-0.985; P < .001). Based on the Youden index, the optimal threshold was >50 mg, with a sensitivity of 96.7% and a specificity of 95.7%.

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.