Preschooler male with acute urinary retention Sagittal US of the pelvis (above) shows an anechoic distended bladder superiorly and an echogenic mass posterior and inferior to the bladder. Axial CT with contrast of the pelvis (below) shows a round heterogenous necrotic mass in the center of the pelvis that is displacing the bladder superior and anteriorly. The diagnosis was rhabdomyosarcoma of the prostate.