Today's Veterinary Practice

NOV-DEC 2018

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CLINICAL INSIGHTS todaysveterinarypractice.com NOVEMBER/DECEMBER 2018 61 the dependent flank. The window is defined as the interface between the homogenous echotexture of the spleen and the ovoid, typical mixed-echogenicity appearance of the kidney. The normal kidney has a hyperechoic outer cortex and a relatively hypoechoic inner medulla. Because both the spleen and the left kidney are mobile, they may not be found immediately adjacent, and small intestine or mesenteric fat may be present in the space between. For many operators, examining the dependent flank is challenging, but external anatomic landmarks can be helpful. ■ Compose a long axis image by placing the probe in the dependent (left) flank caudal to the 13th rib and ventral to the lumbar hypaxial musculature. ■ While maintaining a long axis image, fan dorsomedially to search for the left kidney. ■ With the kidney centered, fan lateral and cranial to identify the spleen. Anechoic material adjacent to renal or splenic parenchyma, between loops of small intestine, or within mesenteric fat represents peritoneal effusion ( FIGURE 3 ). Small volumes of fluid located immediately adjacent to the kidney may be difficult to distinguish as peritoneal or retroperitoneal. Cystocolic Window The primary landmarks used to orient the cystocolic (CC) window are the urinary bladder and the ventral surface of the descending colon. To generate this window, place the probe caudally along midline with the marker oriented cranially to create an image along the long axis of the patient. The body of the urinary bladder is mobile and typically falls to the dependent flank, so it may not be readily apparent on initial probe placement. Too much pressure on the probe can collapse or displace a small volume urinary bladder and make identification challenging. The normal urinary bladder appears as an ovoid structure containing anechoic material, surrounded by a thin echogenic wall with 3 discernible layers. The colon generally contains gas, which generates dirty distal acoustic shadowing and reverberation artifacts originating at the luminal mucosal surface, and/ or feces, which is often associated with clean distal acoustic shadowing. These artifacts will interfere with image generation of structures deep to the colon. If moderate peritoneal effusion is identified at this window, exercise caution when interpreting the appearance of the urinary bladder wall. When a curvilinear interface is bounded on either side by anechoic fluid (e.g., urine within the urinary bladder lumen and peritoneal effusion outside), refraction artifact (also known as edge shadowing, pseudo- urinary bladder rupture, or edge dropout artifact) may occur at the tangential interface with the ultrasound beam, giving the appearance of a discontinuous urinary bladder wall. The appearance of effusion in the CC window ( FIGURE 4 ) should not be confused with a true rupture of the urinary bladder, in which the urinary bladder will be collapsed. Hepatorenal Window The hepatorenal (HR) window can be challenging to obtain, especially in large dogs. The right FIGURE 4. Cystocolic window showing the urinary bladder (UB), descending colon (C), and a large volume of peritoneal effusion (E). The AFAST examination can be performed with the patient in one lateral position. A complete TFAST examination is performed with the patient in alternating left and right lateral recumbency or in sternal recumbency.

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