Minimal renal pelvis dilation in cats diagnosed with benign ureteral obstruction by antegrade pyelography: a retrospective study of 82 cases (2012-2018)

Objectives The aim of the study was to describe renal pelvis (RP) and ureteral ultrasonographic measurements in a population of cats with confirmed benign ureteral obstruction (UO) by antegrade pyelography. The secondary objective was to further describe clinical findings associated with minimally dilated obstructed kidneys in an attempt to better understand its occurrence. Methods Retrospective case series of cats diagnosed with benign UO were confirmed by antegrade pyelography. Medical records were reviewed and signalment, diagnostic imaging results, serum creatinine (SCr) concentration and urine culture results were recorded. Each obstructed kidney was categorized into two groups: group 1 included all RP measurements <= 4 mm and group 2 included all RP measurements >4 mm. Results A total of 82 cats with 114 obstructed ureters met the inclusion criteria. Fifty (61%) cats had a unilateral UO and 32 (39%) had a bilateral UO. Thirty (26%) kidneys were included in group 1 while 84 (74%) were included in group 2. Nine (8%) kidneys had an RP dilation <= 2 mm. Median RP and ureteral diameters were 6.6 mm (range 1.1-37.0 mm) and 3.2 mm (range 0.0-11.0 mm), respectively. RP size correlated positively with ureteral diameter in the study population (P <0.0001), but not in group 1 when analyzed separately (P = 0.47). UO was secondary to stones in 80 (70%) ureters. Seventeen (21%) cats had a positive urine culture. At admission, 79 (96%) cats were azotemic with a median preoperative SCr concentration of 444 mu mol/l (range 108-1326 mu mol/l). The mean (95% confidence interval [CI]) preoperative SCr concentration was significantly higher in group 1 (762 mu mol/l [498-1165 mu mol/l]) than in group 2 (409 mu mol/l [333-502 mu mol/l]). RP size in the two groups correlated negatively with preoperative SCr concentration (P = 0.0002). Conclusions and relevance Feline UO may be associated with minimal RP dilation and the severity of RP and ureteral dilation can be highly variable. Absence of significant RP dilation does not rule out UO in cats.