To investigate the feasibility of morphology and quantitative parameters for evaluation of lymph node metastatic (LNM) potential in papillary thyroid microcarcinoma (PTMC) with dual-energy CT iodine image.

The ninety-five PTMC patients (59 patients with LNM, 36 patients without LNM in the neck) whom underwent dual-energy contrast scanning and confirmed by first postoperative pathology results were enrolled in this retrospective study from July 2014 to December 2016. Dual-energy iodine images were obtained by the dual-energy post-processing software. The iodine image morphology of each patient was analyzed, including size, number, aspect ratio, shape, uncompleted enhanced ring sign, nodule which breaks through the thyroid capsule, microcalcification, and enhanced-degree, and diagnostic efficiency of each imaging feature was calculated. The iodine concentration (IC) and CT value of PTMC solid parts were measured in arterial phase and venous phase images respectively, as well as theNICnod (normalized iodine concentration) and normalized CT value. The independent sample t test was performed to compare quantitative parameters between the LNM group and non-LNM group. ROC curves with quantitative parameters of two phases were used to analyze the diagnostic efficiencies of NIC and normalized CT value.

Statistically, in the iodine image, the imaging features of LNM group, including multiple lesions, maximum diameter of nodules, aspect ratio, irregular shape, uncompleted enhanced ring sign, and nodule which breaks through the thyroid capsule, had significant differences compared with those of non-LNM group in the neck (χ² were 14.965,8.724,11.494,8.097,6.324,23.272;P all<0.05), and there were positive correlations with LNM potential (r were 0.397,0.303,0.348,0.309,0.258, 0.495; P all<0.05), the diagnostic efficiency of nodule which breaks through the thyroid capsule was the highest among the imaging features for diagnosis of cervical LNM (sensitivity 77.9%, specificity 72.2%, accuracy 75.8%). During the artery phase, mean NIC_ROI and normalized CT value of non-LNM group were respectively 0.29±0.10,0.33±0.11,and these of LNM group were respectively 0.45±0.15,0.44±0.13.NIC_ROI and normalized CT value of non-LNM group were less than LNM group′s (t=-4.891,-3.462;P all<0.001). During the venous phase, NIC_ROI and normalized CT value of LNM group were higher than non-LNM group′s (t=-3.381,-2.18; P all<0.05). Among all quantitative parameters, the NIC of arterial phase has the highest diagnostic efficacy for the diagnosis of cervical LNM. The area under the ROC curve (AUC) was the largest, 0.814, the sensitivity was 73.5%, the specificity was 79.2%, and the diagnostic threshold was 0.208.

Dual-energy CT iodine image morphology and quantitative parameters have important clinical value for evaluation of cervical lymph node metastatic potential in PTMC.

Thyroid neoplasms; Tomography, X-ray computed; Iodine; Diagnosis