Utility of MRI Features for Differentiation of Retroperitoneal Fibrosis and Lymphoma

The objective of our study was to retrospectively compare the MRI features of retroperitoneal fibrosis (RPF) and lymphoma presenting as confluent retroperitoneal soft tissue. MRI studies of 31 patients (18 men, 13 women; mean age, 58.4 ± 15.8 [SD] years; 22 with RPF and nine with lymphoma) were evaluated. Two radiologists independently and in consensus evaluated all cases for an array of subjective imaging features. A third radiologist measured the size (i.e., the greatest dimension in the transverse plane) and apparent diffusion coefficient (ADC) value of the tissue. Features of RPF and lymphoma were compared using the Fisher exact test, Mann-Whitney test, and receiver operating characteristic (ROC) curve analysis. Interreader concordance was also calculated. The mean age of patients with lymphoma was significantly greater than that in cases of RPF (72.4 ± 13.3 [SD] vs 52.7 ± 13.2 years, respectively; p = 0.003). The MRI features significantly more common in patients with RPF were pelvic extension (p = 0.004) and medial ureteral bowing (p < 0.001). The MRI features significantly more common in cases of lymphoma were predominantly suprarenal location, perirenal extension, anterior aortic displacement, heterogeneity, and the presence of additional nodes (p < 0.001-0.043). Size was significantly greater in patients with lymphoma than in those with RPF (mean ± SD, 33.9 ± 17.3 vs 11.0 ± 5.7 mm; p < 0.001) and had an area under the curve (AUC) of 0.960; a size larger than 15 mm had sensitivity of 100% and specificity of 86.4% for the diagnosis of lymphoma. The ADC was significantly lower in lymphoma than in RPF (mean ± SD, 0.92 ± 0.17 vs 1.40 ± 0.38 × 10(-3) mm(2)/s; p = 0.003) and had an AUC of 0.904. An ADC of 0.955 × 10(-3) mm(2)/s or less had sensitivity of 83.3% and specificity of 89.5% for the diagnosis of lymphoma. Interreader concordance for subjective features was very good to excellent (range, 80.6-100%). MRI features may be helpful in distinguishing between RPF and lymphoma.