Prediction of Lateral Pelvic Lymph-Node Metastasis in Low Rectal Cancer by Magnetic Resonance Imaging

This study was designed to evaluate the diagnostic accuracy of magnetic resonance imaging (MRI) for lateral pelvic lymph-node metastasis. Eighty-four patients with primary lower rectal cancer were examined by MRI and subsequently underwent radical surgery with lateral pelvic lymph-node dissection, without preoperative treatment. Lateral lymph-node metastases were assessed preoperatively by MRI, and the results were compared with the histopathological findings. The criterion for lateral lymph-node metastasis was any recognizable lymph node in the pelvic wall, regardless of diameter. Lateral pelvic lymph-node metastasis was diagnosed on preoperative MRI in 16 patients (19.9 %). The overall patient-based sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of MRI were 75, 69.1, 36.4, 92.2, and 70.2 %, respectively. When a cut-off value of 10 mm was used for diagnosis, the corresponding values were 43.8, 98.5, 87.5, 88.1, and 88.1 %, respectively. The mean diameter of metastatic nodes (14.7 mm) was significantly larger than that of negative nodes (5.7 mm; P < 0.01). MRI is an effective technique for predicting lateral pelvic node involvement and thus may facilitate preoperative decision-making in rectal cancer treatment. A cut-off value of 10 mm is useful for avoiding unnecessary lateral lymph-node dissection.