The ultrasonographic medullary “rim sign” versus medullary “band sign” in cats and their association with renal disease

Background: Medullary rim sign (MRS) refers to a hyperechoic line in the renal medulla, reported on ultrasound examination (US) in both dogs and cats with and without kidney disease (KD). Objective: To describe the different aspects of MRS in cats and to assess its association with KD. Animals: Cats that underwent US examination, with MRS (study group) with and without KD and without MRS with and without KD (control groups). Methods: Retrospective case-control study: cats with MRS, with or without KD (rim sign groups) and cats without MRS, with or without KD (control groups). Ultrasonographic images were blindly reviewed with attention given to the thickness and margins of the MRS recorded. Results: Eighty-four cats with MRS were included and 60 cats recruited for each control group. The MRS had 2 distinct aspects: a thin hyperechoic line with well-defined margins (MRS-line) in 50/84 cats (59%) and a thick hyperechoic band with ill-defined margins (MRS-band) in 34/84 cats (41%). Twenty of 50 (40%) cats with MRS-line and 25/34 (74%) of cats with MRS-band had KD. The frequency of MRS-line was higher in cats without KD, whereas the presence of MRS-band was more frequent in cats with KD (P =.003). Conclusions and Clinical Importance: A thick hyperechoic ill-defined band (for which the term medullary band sign is proposed) was more frequently associated with KD, whereas a thin hyperechoic well-defined line (true MRS) may be seen in cats with or without KD.