Apparent diffusion coefficient for discriminating metastatic from non-metastatic lymph nodes in primary rectal cancer

Abstract Objective To investigate whether the apparent diffusion coefficient (ADC) could be used to discriminate metastatic from non-metastatic lymph nodes (LNs) in patients with primary rectal cancer. Methods This study investigated 34 patients (male: 12, female: 22, mean: 62.7, range: 37–82) who underwent 1.5-T MRI with diffusion-weighted imaging (DWI) and subsequent surgical resection. A blinded radiologist measured the ADC value in each regional LN after referring to the T2-weighted images and DWI. The t -test was used to compare the mean ADC values of the metastatic and non-metastatic LNs. A ROC analysis was performed to calculate the diagnostic performance and obtain the optimal cut-off. The histopathological results were used as the reference standard. Results 114 LNs (46 metastatic and 68 non-metastatic) were matched and analyzed. The mean ADC of the metastatic LNs was significantly lower than that of the non-metastatic LNs (0.9 ± 0.15 × 10−3 mm2 /s; 1.1 ± 0.22 × 10−3 mm2 /s, P < 0.0001). The area under the ROC curve was 0.734 (95% confidence interval, 0.644–0.812). When an ADC value of 1.0 × 10−3 mm2 /s was used as the cut-off, a maximum accuracy of 72% was calculated (sensitivity, 78%; specificity, 67%). Conclusions Although ADC could be used to discriminate metastatic from non-metastatic LNs, the diagnostic accuracy is approximately 70%.