The characteristics of concomitant thyroid nodules cause false-positive ultrasonography results in primary hyperparathyroidism

Background: Concomitant thyroid nodules are the most common reason for false-positive ultrasonography (US) results in primary hyperparathyroidism. The aims of this prospective clinical Study were to evaluate false-positive US results according to the characteristics of concomitant thyroid nodules and to determine which characteristics of thyroid nodules are important. Study design: This prospective Study included 120 consecutive patients with primary hyperparathyroidism. The patients were divided into 2 groups according to preoperative US results. Group I consisted of 32 patients with false-positive US results and group 2 consisted of 88 patients with true-positive US results. Results: The risk for false-positive US result was increased 25-fold for patients with parathyroid adenoma weight of more than 500 mg (odds ratio [OR], 25; 95% confidence interval [CI], 8.6-74.5), 75-fold for more than I posteriorly located thyroid (OR, 75; 95% CI, 19.3-293.4), 358-fold for the presence of exophytic thyroid nodules (OR, 358; 95% Cl, 42.3-3036), and 423-fold for the presence of posteriorly located thyroid nodules (OR, 423; 95% Cl, 49-3662). Conclusion: Although there was no particular characteristic of concomitant thyroid nodules that contributes to false-positive US results, the posteriorly located thyroid nodules were the strongest Correlate for the false-positive US results to other features. (C) 2009 Elsevier Inc. All rights reserved.