Feline abdominal ultrasonography: what’s normal? what’s abnormal? The kidneys and perinephric space

Abstract

Practical relevance: Abdominal ultrasound plays a vital role in the diagnostic work-up of many cats presenting to general and specialist practitioners. Ultrasound examination of the kidneys and perinephric space can provide important information on several conditions including chronic renal disease, hydronephrosis and perinephric pseudocyst formation. Clinical challenges: Despite ultrasonography being a commonly used modality, many practitioners are not comfortable performing an ultrasound examination or interpreting the resulting images. Even for the experienced ultrasonographer, differentiating between incidental findings, such as a medullary rim sign, and pathological changes can be challenging. Aim: This review, part of an occasional series on feline abdominal ultrasonography, discusses ultrasonographic examination of the normal and diseased kidney and perinephric space. Aimed at general practitioners who wish to improve their knowledge of and confidence in feline abdominal ultrasound, this review is accompanied by highresolution images and videos available online as supplementary material. A subsequent article will address ultrasonography of the collecting system including the renal pelvis and urinary bladder. Equipment: Ultrasound facilities are readily available to most practitioners, although use of ultrasonography as a diagnostic tool is highly dependent on operator experience. Evidence base: Information provided in this article is drawn from the published literature and the author's own clinical experience.

Evaluation of and the prognostic factors for cats with big kidney‐little kidney syndrome

“…Radiography and ultrasonography have both been applied as adequate tools for assessing feline kidneys sizes. However, ultrasonography is also known for the disadvantage to subjectively obtain the longest kidney axis for each measurement as it relies heavily on user expertise, cat preparation, and the ultrasound machine models 9,10 . As a result, radiography was chosen as our main imaging modality for it provides more objective measurement of the kidneys and was not uncommon in our hospital.…”

“…However, ultrasonography is also known for the disadvantage to subjectively obtain the longest kidney axis for each measurement as it relies heavily on user expertise, cat preparation, and the ultrasound machine models. 9 , 10 As a result, radiography was chosen as our main imaging modality for it provides more objective measurement of the kidneys and was not uncommon in our hospital. Furthermore, in practices where only ultrasonography is available, it might be impossible to obtain the length of the second lumbar vertebra for the assessment of kidney size and the absolute values of renal length differences can be also applied for the cats with ultrasonography examination.…”

Renal scintigraphy as an early and efficient method for detecting loss of renal function in a cat

“…In the abdominal ultrasound evaluation (MyLab40; Esaote), the presence of asymmetric kidneys was observed, with a longitudinal axis measurement of 4.2 cm in the left kidney (LK) and 3.4 cm in the right kidney (RK; RI 3.0-4.5 cm). 7 The LK showed a slightly irregular contour, hyperechoic cortices and decreased corticomedullary definition. There was no dilatation of the renal pelvis, but there was a cyst containing anechoic fluid located within the cortex, measuring about 0.14 cm.…”

“…2 Several structural changes are described in the abdominal ultrasonography and/or radiography of cats with CKD, including a decrease in kidney size, loss of corticomedullary definition, irregular renal contour, mineralization of the renal pelvis, and presence of neoplasia, renal cysts, areas of infarction and nephrolithiasis. 4–7 These changes can impair the normal renal parenchyma as they progress, resulting in loss of function. 7,8 There is no evidence that nephrolithiasis without ureteral obstruction is associated with CKD progression in cats.…”

“…4–7 These changes can impair the normal renal parenchyma as they progress, resulting in loss of function. 7,8 There is no evidence that nephrolithiasis without ureteral obstruction is associated with CKD progression in cats. 9 Patients with International Renal Interest Society (IRIS) stage 1 CKD are not azotemic but present changes in kidney structure, such as abnormal renal imaging findings.…”