Renal allografts: evaluation by MR imaging.

The value of magnetic resonance (MR) imaging in assessing renal transplants was prospectively studied in 45 patients with 46 allografts. Four allografts were imaged at two different times, and separate diagnoses were given for both examinations. Therefore, this study was based on 50 proved diagnoses: nine normally functioning allografts, four allografts with acute tubular necrosis (ATN), 29 with acute rejection, one with chronic rejection, five with cyclosporin nephrotoxicity, and two with local inflammation secondary to adjacent abscess. Twenty-seven of the allografts had concomitant fluid collections. Normal renal structures with preservation of corticomedullary contrast (CMC) on T1-weighted images were demonstrated in all the normally functioning allografts. Decreased or absent CMC on T1-weighted images, reflecting a long T1 relaxation time for cortex, was found to be the most consistent sign of acute renal allograft rejection (27/29). No abnormalities on on MR images were observed in allografts compromised by cyclosporin nephrotoxicity. Hydronephrosis of the renal allograft was easily diagnosed with MR. Perirenal abscess (three cases) and perirenal hematomas (five cases), because of their higher MR signal intensity on T1-weighted images (TR = 0.5 sec, TE = 28 msec), could be differentiated from clinically insignificant postoperative fluid seromas (seven cases), lymphoceles (11 cases), and urinoma (one case).