Prevalence and clinical significance of the medullary rim sign identified on ultrasound of feline kidneys

Abstract

ObjectivesThe medullary rim sign (MRS) is an ultrasonographic (US) feature identified in normal and diseased feline kidneys. The prevalence and potential clinical significance of the MRS in a referral hospital cat population was investigated.MethodsRetrospective case–control study. US images from 661 cats were reviewed. Cats with an MRS were identified and compared with equal number of time-matched control cats. Medical data and MRS features, including thickness, intensity and symmetry, were collected. Associations between independent variables and the MRS were examined with conditional and unconditional logistic regression, with initial univariable, and subsequent multivariable analysis.ResultsOf the 661 reviewed cats, 243 (36.8 per cent) showed a variation of the MRS. A thin MRS (133 cats) was not associated with azotaemic renal disease (P=0.87). A thick MRS (110 cats) was associated with azotaemic renal disease (P=0.001). There was an association between the presence of MRS and a final diagnosis of feline infectious peritonitis (FIP) (P=0.028).ConclusionsThe MRS is a common finding in cats. In this cat population, a thick MRS was associated with azotaemic renal disease, while a thin MRS was not. In cases with a clinical suspicion of FIP, the MRS may be related to the underlying disease process and not be an incidental finding.

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

“…The frequency of the MRS‐ line was higher in cats without KD, whereas the MRS‐ band was significantly more frequent in cats with KD. In another study, 10 the presence of an MRS was associated with KD, whereas in our study, no association was found between MRS and KD. Although both studies had the similar objective to investigate the clinical relevance of MRS in cats there were some substantial differences between the studies.…”

“…In this way, some cases may have been missed, because some radiologists may not have reported its presence, because he or she may have assumed it was not clinically relevant. The prevalence of MRS in our population might be underestimated, and this possibility also could explain the lower prevalence obtained compared to the prevalence observed in a previous study (36%) 10 . It was not possible to further characterize the type of KD and correlate MRS with the chronicity of KD.…”

“…A previous study reported an association between presence of a MRS and final diagnosis of feline infectious peritonitis, where a thin, marked intensity MRS was identified (although the association with KD was described for thick MRS) 10 . In our study population, no cats had a diagnosis or suspicion of feline infectious peritonitis.…”

“…Its clinical relevance however still remains unclear. In another study, both presence of MRS and visualization of a thick MRS were associated with KD 10 . In addition, some confusion regarding the definition of MRS persists.…”

“…In a recent study, MRS was identified in both azotemic and nonazotemic cats 9 . Another recent study reported the prevalence and clinical relevance of the MRS in cats 10 . Its clinical relevance however still remains unclear.…”