Figure 9a. Renal arteriovenous fistula in a 48-year-old woman with sudden onset of hematuria and right flank pain. Excretory urography performed 3 days before retrograde pyelography showed nonopacification of the right kidney. (a) Retrograde pyelogram shows nonopacification of the lower pole calices and irregular tortuous filling defects in and around the interpolar calices and pelvis (arrows). The pelvicaliceal system is mildly dilated. (b) Axial contrast-enhanced CT scan obtained during the corticomedullary phase shows tortuous, dilated, enhancing vascular structures (arrow) in the right renal sinus. Note the mildly dilated right renal pelvis and the double-J catheter (arrowhead) in the renal pelvis. (c) Coronal contrast-enhanced T1-weighted MR image (repetition time msec/echo time msec = 111/4.1) shows the tortuous vascular structures with signal void (arrows) along the dilated collecting system. (d) Right renal arteriogram shows the entangled vessels of the arteriovenous communication (arrows), which is sometimes referred to as a cirsoid aneurysm, in the lower polar area of the right kidney.