Role of Diffusion-Weighted Magnetic Resonance Imaging in Detection of Lymph Node Metastasis in Rectal Cancer

Abstract Background Rectal cancer is one of the most common malignancies of the digestive tract, ranking first in the worldwide incidence of malignant tumors. The early diagnosis, accurate staging and early treatment of rectal cancer are key to improve the five-year survival rate. Rectal MRI plays a crucial role in evaluating rectal cancer by providing multiple prognostic findings and imaging features that guide proper patient management. Aim of the Work to evaluate the performance of diffusion-weighted MRI (DWI) for the detection of lymph nodes and for differentiating between benign and metastatic nodes during primary rectal cancer staging. Patients and Methods the study was carried out at Ain Shams University Hospitals, Radiodiagnosis Department on 35 patients, 29 patients were histopathologically proven rectal carcinoma underwent surgical resection and 6 cases were potentially free of cancer considered as control. Results We found that the size of metastatic lymph nodes on DWI was significantly larger than that of non-metastatic lymph nodes (0.97± 0.37 vs. 0.4± 0.17 cm), most of malignant nodes had rounded shape (55.6 %) vs. oval shaped (70.6%) in benign nodes and almost all of metastatic lymph nodes had irregular margin (97.2%) while all benign nodes appeared having smooth margin. The mean ADC value was significantly lower for metastatic lymph nodes than non-metastatic lymph nodes (1.21± 0.54 vs. 1.51± 0.51 x 103 mm²/sec). In addition, for evaluation of lymph node metastasis that reflects the primary tumor characteristics, the LN/T ratio (defined as the ratio of lymph node ADC value to the primary tumor ADC value) was calculated. It was significantly lower for metastatic lymph nodes than non-metastatic lymph nodes (1.06± 0.37 vs. 1.65± 0.73). Receiver operating characteristic curve analysis revealed that the best performing cutoffs were 0.5 cm for lymph node size, 0.987 x 103 mm²/ sec for ADC value, and 0.762 for LN/T ratio. Accuracy was significantly greater for lymph nodes with irregular margin (92.3%), than LN/T ratio (78.5%) than for lymph node size (62.0%) or ADC value (74.8%). Conclusion Preoperative DWI, especially the margin of lymph nodes as well as LN/T ADC ratio, are recommended for evaluation of lymph node metastasis in patient with rectal cancer.