The Impact of Arterial Phase on the Detection of Cervical Lymph Node Metastasis From Papillary Thyroid Carcinoma: A Quantitative Evaluation on Multiphasic Computed Tomography.

OBJECTIVE: The purpose of this study was to assess the diagnostic performance of multiphasic computed tomography (CT) in the discrimination of metastatic lymph nodes (LNs) of papillary thyroid cancer by using quantitative parameters. METHODS: This study enrolled 272 pathologically proven metastatic and benign LNs. Multiphasic CT was utilized by using nonenhanced, arterial (25-second delay), and venous (80-second delay) phases. Mean tissue attenuation values (MAVs) of metastatic and benign LNs were measured, and normalized MAV (common carotid artery and paraspinal muscle) and wash-in and wash-out percentages were also calculated. RESULTS: The arterial phase showed the highest diagnostic performance in differentiation (area under the curve +/- standard error, 0.97 +/- 0.02; 95% confidence interval, 0.94-1.0; P < 0.001). Cutoff values for MAVs, normalized MAVs, and wash-in and wash-out percentages to predict metastatic LNs were calculated as 109 HU, 0.33, 1.93, 122.5, and -5.6 (sensitivity: 93.4%, 93.3%, 90.4%, 94.1%, and 97.8%, and specificity: 99.3%, 90.4%, 98.5%, 92.6%, and 99.3%, respectively). CONCLUSIONS: Early-phase enhanced CT and the use of quantitative parameters derived from multiphasic CT improve the detection of cervical lymph node metastasis from papillary thyroid cancer.