Today's Veterinary Practice

JAN-FEB 2018

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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PEER REVIEWED 84 IMAGING ESSENTIALS Jejunum The jejunum is evaluated in its entirety by sweeping the transducer back and forth (side to side) across the abdomen in an overlapping pattern, beginning cranially and slowly progressing caudally. It may not be possible to trace the jejunum continuously from orad to aborad due to gas interposition or shadowing artifacts from intestinal contents. NORMAL ULTRASONOGRAPHIC FEATURES OF THE GASTROINTESTINAL TRACT Before imaging the gastrointestinal tract, the patient should be fasted, however, this may not be feasible in all circumstances. Ideally, fasting will prevent ultrasound artifacts, such as reverberation artifact and beam attenuation, 1 from impeding the structures either adjacent and dorsal to the gastrointestinal tract or the far wall of the gastrointestinal tract that is being imaged. Reverberation artifact appears as multiple, equidistantly spaced linear reflections ( FIGURE 1 ). This artifact occurs when multiple echoes are erroneously processed due to a delayed return of the signal. 1 Beam attenuation appears as a reduction of the ultrasound signal at depth in the far field ( FIGURE 2 ). This is due to the attenuation of the ultrasound beam in the near field secondary to gastrointesinal contents. 1 The layering of the walls of the gastrointestinal tract can be assessed using ultrasonography and has a characteristic pattern of alternating hyper- and hypoechoic layers ( FIGURE 3 ); the luminal- mucosal interface, submucosal, and serosal layers are hyperechoic; and the mucosal and muscularis layers are hypoechoic. An easy mnemonic is M&M's (mucosa and muscularis) are chocolate (dark/hypoechoic). The gastrointestinal tract layering is as follows from the lumen, centrally, to the serosal margin, peripherally: 1. Interface between lumen and mucosa (hyperechoic) 2. Mucosa (hypoechoic) 3. Submucosa (hyperechoic) 4. Muscularis (hypoechoic) 5. Serosa (hyperechoic) FIGURE 1. Longitudinal axis of a cat stomach filled with gas. Notice the dirty shadowing created by the gas reverberation artifact deep to the superficial stomach wall. FIGURE 2. Longitudinal axis of the stomach in a cat. Note the hyperechoic line on the luminal side of the stomach. The material in the stomach hyperattenuates the ultrasound waves so that it is totally black in the deep portion of the image. FIGURE 3. Longitudinal axis view of a segment of jejunum of a normal dog demarcating the different layers of the small intestines.

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