Acute renal allograft rejection: difficulty in diagnosis of histologically mild cases by MR imaging.

To determine the ability of magnetic resonance (MR) imaging to diagnose various degrees of acute allograft rejection (AR), 33 MR examinations in 28 patients were obtained. Surface coils were used in 21 examinations. Seventeen examinations were correlated with biopsy results, which were graded as absent (n = 7), mild (n = 6), or severe (n = 4) AR. Corticomedullary differentiation (CMD) on T1 weighted images was graded as absent/poor versus distinct, and images were also evaluated for visibility of intrarenal vessels. For serial examinations, renal volume was measured and compared. The MR results were correlated with radionuclide interpretations in 22 cases. Diminished CMD was most common with AR (7 of 12) but was also seen with acute tubular necrosis (2 of 6) and cyclosporin toxicity (2 of 3). All four cases of severe AR had diminished CMD. In contrast, only one of six cases of mild AR had diminished CMD (p less than 0.05). Four of five cases of mild AR by radionuclide scan were correctly diagnosed. Visualization of intrarenal vessels was best with surface coils, but this did not contribute to differential diagnosis. Renal volume was increased in rejecting allografts. Magnetic resonance is a promising modality for investigation of renal allografts but is not a sensitive or specific modality for the diagnosis of mild AR.