[A case of retroperitoneal fibrosis with special emphasis on diagnosis using the magnetic resonance imaging].

A case of idiopathic retroperitoneal fibrosis (RF) is reported. MRI showed a low signal intensity on T1 and heterogeneous signal intensity on T2-predominant image. Although this could be demonstrated either in malignant RF or early stage of non-malignant RF, differentiation from malignancy was made from the quick response to steroid therapy.