Parathyroid incidentalomas detected on routine ultrasound-directed fine-needle aspiration biopsy in patients referred for thyroid nodules and the role of parathyroid hormone analysis in the samples

Background: The widespread use of high-resolution ultrasound (US) has allowed the detection of not only nonpalpable thyroid nodules but also parathyroid incidentalomas in the general population. We sought to determine the prevalence of parathyroid incidentalomas in a large group of patients referred for US-guided fine-needle aspiration biopsy (FNAB) of suspected thyroid nodules and to investigate the role of additional parathyroid hormone (PTH) analysis in the washouts of FNAB of suspicious papathyroid nodules in these patients. Methods: Between June 2006 and December 2007, US-guided FNAB (US-FNAB) was performed in 6469 patients. Among them, 112 patients (1.7%) underwent additional PTH analysis in FNAB washouts (FNA-PTH) due to suspected parathyroid lesions. A retrospective review of clinical, radiologic, cytologic, and pathologic records was conducted. We evaluated the prevalence of parathyroid adenomas that were detected on thyroid US incidentally as well as the results of FNAB and FNA-PTH in parathyroid adenomas that were confirmed histopathologically. Results: Parathyroid incidentalomas were identified in 14 patients based on pathology and 10 patients based on elevated FNA-PTH. The occurrence of parathyroid incidentalomas was 0.4% (24/6496) on thyroid US. For the detection of the incidentalomas, the positive predictive value (PPV) of thyroid US was 21.4% (24/112). When an inadequate specimen was considered as being of nonparathyroid origin, the sensitivity of FNAB was 41.7%, specificity was 97.7%, accuracy was 85.7%, PPV was 83.3%, and negative predictive value (NPV) was 86% in 112 patients. The diagnostic performance of FNA-PTH in 18 operated nodules showed a sensitivity of 92.9%, specificity of 100%, accuracy of 94.4%, PPV of 100%, and NPV of 80%. Four patients noticed symptoms related to hyperparathyroidism after FNA-PTH analysis. Conclusions: The prevalence of parathyroid incidentaloma was 0.4% (24/6496) in a large series of patients referred for suspected thyroid nodules. The use of FNA-PTH combined with FNAB can help clinicians accurately diagnose parathyroid incidentalomas at the time of US-guided FNAB.