Abdominal Ultrasound in the Horse

Ultrasonographic evaluation of the abdomen is extremely useful in characterizing certain components of the disease process in the foal or horse with colic. The findings of the abdominal ultrasound can distinguish surgical and medical colic patients. It is a very useful non-invasive diagnostic tool and can be used to guide other techniques such as abdominocentesis. It can be carried out trans-abdominally or trans-rectally. The latter scenario is useful for confirming andormalities palpated on prior rectal examinations. This technique is limited in large horses as the ultrasound beam cannot penetrate further than 30 cm and some images can be obstructed by the gas within the ultrasound lumen interfering with the beam. In general, a 3.0-MHz or 5.0 MHz zector scanner is used. The 3.0-MHz scan head can penetrate deeper than the 5.0-MHz head but with a loss of clarity of the image. In adult horses, images of the large intestine can be achiever by scanning between the intercostal space, flank and the ventral abdomen. It may be possible to see a portion of the jejunum by scanning the midventral abdomen in some horses. In foals, it is possible to see both large and small intestine by scanning the ventral abdomen.

The horse should be restrained in stocks ideally. The desired region is clipped and a generous quantity of coupling gel is applied. The liver can be viewed from both left and right sides, however if there is a reduction in hepatic mass then it will be easier to view it from the left side, between the 7th and 9th intercostal spaces. The hepatic architecture, size, location and dimensions of the hepatic veins and bile ducts should be noted. The spleen can be visualised from the left hand side between the 8th and 17th intercostal spaces. The same parameters should be noted.

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