The ultrasonographic appearance of renal medullary striations and their association with renal disease and renal histopathology in domestic cats

Medullary striations (MS) have been anecdotally observed on ultrasound of feline kidneys; however, their significance is unknown. Aims of this retrospective, case control, pilot study were to describe the appearance, prevalence, and clinicopathological correlates of MS in a referral feline population. Still images from 1247 feline abdominal ultrasound studies performed between 2011 and 2021 were reviewed. Cats with MS were identified and compared with age-matched controls. Serum urea, creatinine, calcium, phosphate, and calcium-phosphate-product, plus urine specific gravity, urine protein: creatinine ratio (UPC), prevalence of active sediment (defined as > 5 red (RBC) or white blood cells (WBC) per high-power field) and prevalence of positive urine culture were compared between MS and control groups using the Mann-Whitney U test or Fisher's Exact test. Data are presented as median [range]. 27 cats were identified as having MS, giving a prevalence of 2.2% with a significantly higher proportion being seen in males (P = 0.018). Medullary striation cats had significantly higher UPC values than controls (0.46 [0.16-7.57] vs. 0.16 [0.07-2.27]; P = 0.006). Cats with MS were more likely to have active urinary sediments (39% vs 8%, P = 0.023), but no difference in prevalence of positive urinary cultures was observed between groups. There was no significant difference in other parameters between MS and control cats. Renal histopathology performed in three MS cats revealed focal regions of linear medullary fibrosis. Medullary striations are associated with proteinuria and urinary tract inflammation in cats, which may reflect renal tubular dysfunction and/or inflammation. Hence identification might allow for earlier detection of renal pathology.