Renal pelvic dilatation seen on ultrasound may be due to a variety of causes. This retrospective study reviewed ultrasound images of 81 dogs and 66 cats with renal pelvic dilatation. Six groups were formed based on medical records: (1) clinically normal renal function; (2) clinically normal renal function with dieresis; (3) pyelonephritis; (4) noninfectious renal insufficiency; (5) outflow obstruction; and (6) miscellaneous nonobstructive anomalies. Although pelvic width in group 1 was lower than the other groups, the difference was not statistically significant from group 2. Renal pelvic width ≥ 13 mm was 100% predictive of dogs and cats with outflow obstruction (group 5). These results confirmed that renal pelvic dilatation can be detected in dogs and cats with normal renal function and that dogs and cats with renal insufficiency, pyelonephritis, or outflow obstruction had increased renal pelvic dilatation. Pylectasia is a term used to describe mild to moderate nonobstructive renal pelvic dilatation that can be seen in patients. Causes of pylectasia include receiving intravenous fluids and/or diuretics, pyelonephritis, and other causes of acute or chronic renal insufficiency. The wide range of variation within the groups indicates that renal pelvic dilatation should be interpreted cautiously.

Commentary: Although renal pelvic dilatation has been often recognized sonographically, size of the renal pelvis, range of values in normal cats and dogs, and the causes of enlargement were largely unknown. Although this was a small study, it will add to the knowledge of renal pelvic dilatation. Prospective studies will be useful to further delineate the causes of renal pelvic dilatation and the impact of other sonographic finds.—Patricia Thomblison, DVM, MS

Clinical significance of renal pelvic dilatation on ultrasound in dogs and cats. D’Anjou M-A, Bedard A, Dunn ME. VET RADIOL ULTRA-SOUND doi 10.1111/j.1740-8261.2010.01729.x(epub ahead of print)