Utility of Preoperative Imaging for Predicting Pelvic Lateral Lymph Node Metastasis in Lower Rectal Cancer

This study aimed to investigate the diagnostic power of preoperative imaging for lateral pelvic lymph node (LPLN) metastasis. A total of 79 patients with advanced lower rectal cancer were preoperatively examined with pelvic enhanced computed tomography and underwent primary resection and LPLN dissection (LPLD) from 2007 to 2014 in our institute. The maximum LPLN was selected to be measured in both the long- and short-axis diameters by picture archiving and communication system (PACS) and was compared with the histopathological results. Receiver operating characteristic (ROC) curves were used to identify the optimal cut-off scores, and we evaluated the accuracy of the thresholds. Twenty-one patients (26.6%) had LPLN metastasis. In the ROC analysis, the criterion of 7.6 mm or larger in the long-axis diameter was used as the optimal threshold for metastasis (area under the curve (AUC) = 0.938) and the criteria of 5.5 mm or larger in the short axis (AUC = 0.946). On the basis of these cut-off scores, the criteria in the long axis represented 95.2% sensitivity, 91.5% specificity, 83.3% positive predictive value (PPV), 98.2% negative predictive value (NPV), and 93.7% accuracy. In contrast, there was 95.2% sensitivity, 89.7% specificity, 76.9% PPV, 98.1% NPV, and 91.1% accuracy in the short axis. Preoperative PACS imaging was considered an optimal tool for diagnosing LPLN metastasis in patients with advanced lower rectal cancer. It is suggested to become the index for considering LPLD adaptation.