Diffusion-weighted Magnetic Resonance Imaging for Detecting Lymph Node Metastasis of Rectal Cancer

Background Preoperative diagnosis of lymph node metastasis is important in determining the optimal therapy for rectal cancer. It has been shown that diffusion-weighted magnetic resonance imaging (DWI) is a useful tool for detecting malignant tumors. Methods One hundred twenty-nine consecutive patients with rectal cancer were examined with DWI + conventional (T1-weighted and T2-weighted) MRI and computed tomography (CT). All 129 patients underwent rectal resection with total mesorectal excision. Findings on DWI + conventional MRI and CT were compared with those from histopathologic examinations. Results Fifty-nine (46%) patients had metastatic lymph nodes on histopathologic examinations. Two hundred twenty (18%) of 1,250 lymph nodes were pathologically positive for tumor metastasis. The overall patient-based sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of DWI + conventional MRI were 93, 81, 81, 93, and 87%, respectively. Corresponding values of CT were 73, 79, 74, 77, and 76%, respectively. The overall node-based sensitivity, specificity, PPV, NPV, and accuracy of DWI + conventional MRI were 97, 81, 52, 99, and 84%, respectively. Corresponding values of CT were 86, 80, 48, 96, and 81%, respectively. Conclusion DWI + conventional MRI is effective for the detection of lymph node metastasis and useful for selection of the optimal therapy for rectal cancer.