MR in renal disease: importance of cortical-medullary distinction

The diagnostic value of MR contrast between renal cortex and medulla (CMC) as an indicator of renal disease was retrospectively studied in 51 patients (9 patients with obstructive disease, 7 with inflammatory disease, 12 with various noninfectious parenchymal medical disease, 5 with vascular disease, 2 with diffuse neoplastic disease, 7 with hemosiderosis, and 10 with renal trauma [blunt trauma and 9 postlithotripsy]). Additionally, normal kidneys from 20 control subjects were studied. On T1-weighted spin-echo images (SE 500/30), CMC was visible in all the normal kidneys (19% contrast +/- 2% SD). A decrease in or an absence of CMC on T1-weighted images (SE 500/28) was found to be a sensitive but nonspecific sign in most of the renal diseases studied. CMC was visibly preserved at normal levels in 7 of the 9 kidneys traumatized by lithotripsy and in all 4 kidneys with acute renal obstruction; CMC was above normal in kidneys with hemosiderosis. In conclusion, alteration in CMC is a sensitive but nonspecific indicator of renal disease. Furthermore, normal CMC can be seen in the presence of renal pathology.