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Imaging the Urinary Tract

Laura Armbrust, DVM, DACVR

Gregory F. Grauer, DVM, MS, DACVIM

Imaging

|November 2015|Peer Reviewed

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Radiographic and ultrasound imaging—in addition to history, physical examination, and clinicopathologic testing—are often used to provide diagnostic information in dogs and cats with known or suspected urinary tract disorders. Although ultrasound has largely become the first-choice imaging modality for small animal urinary tract disease, radiographic imaging is complementary to ultrasonography; both should be employed to evaluate cases whenever possible. 


Imaging of the Kidneys

Survey abdominal radiographs (Figures 1 and 2) offer important information on kidney number, size, shape, symmetry, and location, as well as the presence of any mineralized opacities (eg, calcified tissue, nephroliths). The utility of abdominal radiographs is decreased in patients with abdominal fluid or lack of abdominal fat (eg, young or emaciated patients) because of lack of contrast. Excretory urography (IV pyelography), although more invasive, can augment survey radiographs and provide information about renal parenchymal architecture (eg, filling defects associated with cysts or infiltrative disease), the renal pelvis, and ureters as well as a qualitative assessment of global and individual renal excretory function (Figure 3). 

Similar to survey radiography, ultrasonography can document the number, size, shape, and location of the kidneys as well as the presence of mineralized tissue and nephroliths. In contrast to radiography, abdominal fluid or lack of abdominal fat does not limit the utility of ultrasound. The major advantage of ultrasound for evaluating kidney disease is its ability to assess the internal renal architecture and perirenal tissues. Both focal and diffuse lesions are recognized. Focal lesions may be solid, either homogenous or heterogenous, or fluid in nature. Diffuse lesions (Figures 4-8) may uniformly affect the parenchyma or be heterogenous. The renal cortex, medulla, or both regions may be affected depending on the disease process. 

Related Article: Feline Polycystic Kidney Disease

Renal pelvic dilation (pyelectasia) and proximal ureteral dilation are readily observed with ultrasound and renomegaly may be seen on radiographs if dilation is severe (Figures 9 and 10). Ultrasound can also be used to guide fine-needle aspiration and tissue biopsies of the kidney and fluid aspiration from a dilated renal pelvis. The major limitation of ultrasonographic evaluation of the kidneys is operator experience and expertise.

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