Figure 1. A 38-year-old male with presacral retroperitoneal fibrosis (case 1). (a) Transrectal colour Doppler ultrasound in transverse plane shows a homogeneous, hypoechoic mass with irregular infiltration in the space between the rectum and sacrum (arrowheads). The mass does not reveal flow signal. (b) Contrast-enhanced CT in the level of sacrum shows a presacral soft tissue mass infiltrating into the perirectal space (arrowheads). The bladder wall is thickened posteriorly (black arrowheads). (c) Photomicrograph ( x 200: haematoxylin–eosin stain) shows proliferative fibroblasts with inflammatory infiltrate of lymphocytes, plasma cells and eosinophils.