Most dogs with medullary rim sign on ultrasonography have no demonstrable renal dysfunction

The medullary rim sign is a distinct hyperechoic line in the renal medulla parallel to the corticomedullary junction that has been reported in dogs wi th a variety of renal diseases. To examine the association between medullar y rim sign and renal disease, the medical records of thirty-two dogs that h ad medullary rim sign were reviewed retrospectively. Eighteen dogs (56%) ha d no evidence of renal dysfunction; 14 (44%) had clinicopathological eviden ce of renal disease, including 6 (19%) that had hypercalcemic nephropathy. Most dogs (72%) in which medullary rim sign was the only ultrasonographic f inding affecting the kidneys had no evidence of renal dysfunction. In contr ast, 78% dogs that had medullary rim sign and other renal signs (reduced si ze, increased medullary echogenicity, and pyelectasia) had renal disease. O n the basis of this study, the medullary rim sign appears to be a non-speci fic ultrasonographic sign; however, the possibility cannot be excluded that is a sentinel sign of subclinical renal disease.