MR evaluation of retroperitoneal fibrosis

Purpose: Retroperitoneal fibrosis (RPF) is a rare fibrosing process. The relation of contrast enhancement within the fibrosis and the psoas muscle was suggested for the evaluation of disease activity and response to treatment, but no standardized method for the quantification of the disease activity is currently available. We introduce an MR parameter for the evaluation of RPF. Materials and Methods: 29 patients with untreated idiopathic RPF were examined before medical therapy and after three months of treatment. MR analyses included quotients of T 1 and T 2-signal intensities between the RPF and the psoas muscle. Furthermore, we examined the dynamic contrast enhancement of the fibrous tissue. The respective data were compared with the extent of the RPF after 3 months. Results: In the follow-up examinations we observed a significant regression in 37.9 % (n = 11) of cases, a mild regression in 48.3 % (n = 14) and a stable extent in 13.8 % (n = 4). Patients with a significantly reduced extent showed the highest mean values for the applied MR quotients in the initial examination. The lowest mean values for the respective parameters were found for the group with a stable extent. Only dynamic enhancement quotients showed statistically significant differences (p = 0.011) between the groups of response. Conclusion: We observed a significant reduction in the fibrous tissue after pharmacological treatment in patients with an elevated dynamic enhancement quotient in the initial examination. (orig.)