Ultrasound-Guided Fine Needle Aspirations of Thyroid Nodules: Assessment of Nondiagnostic Samples

Kang, Min Ho; Lee, Ji Hye; Bae, Il Hun; Han, Gi Seok; Cha, Sang Hoon; Kim, Sung Jin; Park, Kil Sun; Koong, Sung Soo

Abstract

PURPOSE
To determine the frequency of malignancy among the nondiagnostic specimens by ultrasound-guided, fine needle aspiration (US-FNA) and to analyze the factors which cause the nondiagnostic specimens of thyroid nodules. MATERIALS AND METHODS: Data were collected from 425 patients (58 male, 367 female) who underwent US-FNA of the thyroid nodule between February, 2002 and October, 2003. The study included 784 nodules from 425 patients. US-FNA was performed 1 to 3 times by two radiologists using a 10MHz linear probe and a 21-gauge fine needle. The percentage of total nondiagnostic specimens was obtained and the percentage of nondiagnostic specimens according to the thyroid nodule's size and nature was analyzed. Thyroid nodules were classified according to their sizes and natures. The nodules were divided by size as either 1cm or more, or less than 1cm in diameter. Each nodule was classified as cystic (pure cystic), mixed (solid portion of nodule<2/3) or solid (solid portion of nodule >2/3). The percentage of malignancy among nondiagnostic specimens was determined and compared to the malignancy rate among diagnostic specimens. Chi-square test and Fisher's exact test were used for statistical significance. RESULTS: Among the 784 nodules, 95 (12.1%) were nondiagnostic. The percentage of nondiagnostic specimens increased as the cystic content increased (p<0.0001). The malignancy rate of the diagnostic specimens was higher than that of the nondiagnostic specimens, but the difference was not significant. CONCLUSION: The cystic content of each nodule was the only significant predictor of nondiagnostic specimens. There was no significant difference in malignancy rate between nondiagnostic and diagnostic specimens. It is suggested that when evaluating an initially nondiagnostic US-FNA, repetitive US-FNA or follow-up USG should be performed.