Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

388 Small Animal Radiolo g y and Ultrasono graphy
Fig. 3-168 Longitudinal (A and B) and transverse (C to F)
sonograms of the left kidney of a 4-year-old castrated male
Siamese cat with a history of polyuria, polydipsia, and palpably
enlarged kidneys. The kidney is hyperechoic with poor corticomedullary
distinction. The renal pelvis is dilated (arrows).
There is peritoneal fluid (C). These findings are indicative of
infiltrative or inflammatory renal disease. Diagnosis:
Lymphoma.
A
B
C
D
E
F
poor prognosis. 495-497 An echogenic region in the renal medulla also has been reported in
association with leptospirosis. 498
Hyperechoic focal lesions within the renal pelvis may occur with renal calculi (Fig.
3-176). 481,483,500,505 Renal calculi may or may not cause shadowing, and it may be difficult
to discriminate between renal calculi and renal pelvic mineralization in the absence of
hydronephrosis. Identifying a dilated renal pelvis around the calculus may help in its recognition.
The size of the renal calculus is important in determining whether or not it forms
a shadow, but the amount and type of surrounding tissue will also affect the stone’s ability
to produce a shadow. Thicker and less uniform surrounding tissue reduces the amount of
shadowing. Chemical composition has little effect on the amount of shadowing. 192
Small amounts of perirenal fluid, either retroperitoneal or subcapsular, may be
detected using ultrasonography. The exact location of the fluid may be difficult to
define; however, if the fluid follows the contour of the kidney, it is probably subcapsular
(Fig. 3-177). An anechoic zone will be observed around the kidney. The echo intensity of
the kidney may be artifactually increased if a large amount of perirenal or peritoneal fluid
is present. This may be seen with renal trauma and hemorrhage, increased renal pelvic
pressure and leakage at or around the parenchymal–collecting system junction, or occasionally
in severe renal inflammation as well as perinephric inflammation or abscess (Fig.
3-178). The only way to clarify the specific characteristics of the fluid is to sample it, usually
by sonographically guided fine-needle aspiration.
DOPPLER ULTRASONOGRAPHY IN RENAL DISEASE
Although oversimplified for the sake of brevity, Doppler ultrasonography is the study of
the blood flow characteristics in both the systolic and diastolic phases of the circulatory