An unusual case of retroperitoneal fibrosis.

With several hundred cases reported there is still much speculation about the etiology of idiopathic retroperitoneal fibrosis. We report an unusual case of retroperitoneal fibrosis with histologically identical lesion in the maxillary sinus, which has not been previously described. Both lesions showed dramatic response to corticosteroids but relapsed frequently on withdrawal of steroids, highlighting the importance of long-term follow-up.