Abstract
Background:
Sonographic measurement of the renal pelvis is often used in the diagnosis and management of ureteral obstruction. However, much of the veterinary literature fails to detail the measurement techniques utilised.

Aim:
This study of renal pelvis assessment methods aimed to compare the interobserver variability of subjective assessments with those of standardised, objective measurements.

Methods:
Sonographic images of the renal pelvis from 15 cats with fluoroscopically confirmed ureteral obstruction were reviewed by six independent observers using 11 methods. Subjective (3) and objective (8) assessments of renal pelvic size in the dorsal, sagittal and transverse planes were created (45 images). Intraclass correlation coefficient (ICC) was calculated to assess interobserver agreement for each measurement method. A two-way random effect model and a single rater (quantitative) and Fleiss (categorical) kappa were calculated.

Results:
Subjective assessment methods had the lowest interobserver agreement in every plane (transverse: κ = 0.326, sagittal: κ = 0.311, dorsal: κ = 0.473). The standardised measurements with the highest interobserver agreement measured the distance between the renal crest and the ureter in dorsal (ICC = 0.91) and transverse planes (ICC = 0.907).

Conclusion:
Subjective assessment of pyelectasia is variable and standardised measurements should be used when sonographically assessing renal pelvic size. Consistent use of the method with the greatest interobserver agreement is likely to improve comparability between studies and ensure appropriate implementation of their findings in a clinical setting.

Key words: Hydronephrosis; Measurement; Pelvis; Pyelectasia; Renal.