ADC maps in the prediction of pelvic lymph nodal metastatic regions in endometrial cancer

OBJECTIVES: To evaluate the usefulness of apparent diffusion coefficient (ADC) in discriminating metastatic from non-metastatic pelvic lymph nodal sites in endometrial cancer. MATERIALS AND METHODS: This retrospective study included 40 patients with endometrial cancer who underwent MRI [T2-weighted, dynamic T1-weighted images and diffusion-weighted images with body background suppression (DWIBS), b-values 0 and 1,000 s/mm(2)], total hysterectomy and pelvic lymphadenectomy. Lymph nodes identifiable on DWIBS were evaluated, classified into six nodal regions, and for each node ADC values, short- and long-axis diameters were measured by two readers. Histopathological findings and follow-up information served as the reference standard. RESULTS: Average (± standard deviation) mean and minimum ADC region value (0.87 ± 0.15 and 0.74 ± 0.07 × 10(-3) mm(2)/s) of metastatic sites (n = 7) were significantly lower than those of non-metastatic ones (n = 89; 1.07 ± 0.20 and 1.02 ± 0.20; p-value = 0.010 and 0.0004). Mean short-axis and short-to-long axis ratios of metastatic nodes were 7.47 mm and 0.68. Using the minimum ADC region value with threshold 0.807 × 10(-3) mm(2)/s, sensitivity, specificity, positive and negative predictive value and accuracy were 100 %, 98.3 %, 63.6 %, 100 % and 98.3 %, respectively (reader 1). CONCLUSION: In endometrial cancer, mean and minimum ADC region values of metastatic nodal sites are significantly lower than those found at normal sites. KEY POINTS : • Magnetic resonance imaging is widely used for endometrial cancer. • Nodes involved with metastases show lower ADC values than normal nodes. • ADC values show higher diagnostic performances than conventional size criteria. • Minimum region ADC values perform better than mean region ADC values. • The radiologist can indicate to the surgeon which nodal stations are involved.