A Logistic Model Including Risk Factors for Lymph Node Metastasis Can Improve the Accuracy of Magnetic Resonance Imaging Diagnosis of Rectal Cancer

Background: To evaluate use of magnetic resonance imaging (MRI) and a logistic model including risk factorsfor lymph node metastasis for improved diagnosis. Materials and
Methods: The subjects were 176 patients withrectal cancer who underwent preoperative MRI. The longest lymph node diameter was measured and a cut-offvalue for positive lymph node metastasis was established based on a receiver operating characteristic (ROC) curve.A logistic model was constructed based on MRI findings and risk factors for lymph node metastasis extractedfrom logistic-regression analysis. The diagnostic capabilities of MRI alone and those of the logistic model werecompared using the area under the curve (AUC) of the ROC curve.
Results: The cut-off value was a diameter of5.47 mm. Diagnosis using MRI had an accuracy of 65.9%, sensitivity 73.5%, specificity 61.3%, positive predictivevalue (PPV) 62.9%, and negative predictive value (NPV) 72.2% [AUC: 0.6739 (95%CI: 0.6016-0.7388)]. Age (<59)(p=0.0163), pT (T3+T4) (p=0.0001), and BMI (<23.5) (p=0.0003) were extracted as independent risk factors forlymph node metastasis. Diagnosis using MRI with the logistic model had an accuracy of 75.0%, sensitivity 72.3%,specificity 77.4%, PPV 74.1%, and NPV 75.8% [AUC: 0.7853 (95%CI: 0.7098-0.8454)], showing a significantlyimproved diagnostic capacity using the logistic model (p=0.0002).
Conclusions: A logistic model including riskfactors for lymph node metastasis can improve the accuracy of MRI diagnosis of rectal cancer.