Figure 6c. Complicated renal arteriovenous malformation in a 66-year-old man who presented with acute right flank pain and hematuria. (a, b) Initial unenhanced helical CT scans show a complex cystic mass of the right kidney with peripheral calcification (arrows in a) and blood within the bladder and right collecting system (b). No obstructing stone was found. Air within the bladder was secondary to Foley catheter placement. (c) Angiogram helps confirm the presence of a large arteriovenous malformation (arrows), as did the results of pathologic examination.