Fig. 1. Renal transplant MRA demonstrates no significant stenosis of the transplant renal artery. Fig. 3.CO2 arteriogram demonstrates two transplant renal arteries.   Case Reference No. CC-0498-05 A 38-year-old man with a history of cadaveric renal transplant presented with hypertension and a serum creatinine of 1.7 µg/dL. The patient underwent a biopsy of his transplant kidney. A transplant renal artery magnetic resonance angiography (MRA) demonstrated no significant stenosis of the transplant renal artery (Fig. 1). The delayed phase of the MRA demonstrated the patent transplant renal vein (Fig. 2). Review of the operative note from the renal transplant revealed that the patient had two Carrel patch anastomoses. Because the MRA did not image the second transplant renal artery, an arteriogram was obtained 2 weeks after the renal transplant biopsy. Because of the elevated creatinine, the arteriogram was initially performed with hand injection of CO2 via a straight flush catheter in the ipsilateral iliac artery. The CO2 arteriogram demonstrated both the main transplant renal artery and a smaller accessory artery to the lower pole with no significant stenosis of either artery (Fig. 3). However, the arterial phase revealed early filling of the transplant renal vein consistent with an AV fistula (Fig. 4). In order to obtain better images, iodinated contrast material was then used via power injector. Interestingly, these images did not reveal the AV fistula (Figs. 5, 6). The AV fistula was also not seen by ultrasound the next day. AV fistulas are relatively common after biopsy but most are subclinical and resolve spontaneously. CO2 has a very low viscosity compared to iodinated contrast material, accounting for its greater sensitivity in detecting this AV fistula. CO2 has also been used successfully to detect minute hemorrhages.		Fig. 2. Delayed phase of the MRA demonstrates a patent transplant renal vein. Fig. 4. CO2 arteriogram shows early filling of the transplant renal vein during the arterial phase. Fig. 5. Arteriogram obtained with iodinated contrast material shows patent transplant renal arteries but no AV fistula.   Fig. 6. Arteriogram obtained with iodinated contrast material-nephrogram phase.
Questions: 1) Has anyone else seen a case similar to this? 2) Does the fact that the AV fistula only filled with CO2 and not with iodinated contrast material mean that the AV fistula is not clinically significant? 3) Was the ultrasound necessary? 4) Is further imaging follow-up of this lesion required (ultrasound, arteriography, MRA)?