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The gastro-intestinal tract does not, in general, lend itself to ultrasound examination, as the presence of solid ingesta or fecal material and the accumulation of intraluminal gas impair the image quality. However, useful information can be gleaned from examination of those parts of the tract which are fluid filled.
In order to image stomach and duodenum, the animal is to fasted for 12 hours, but allowed to drink water just before the examination. Ultrasound examination or GI tract should be performed before administration of barium, as this will interfere with image quality.
Normal appearance: The fluid filled stomach is well-circumscribed structure. The contents are anechoic, but often contain echogenic particles representing air bubbles or food particles, which can be seen swirling around. Peristaltic movement is apparent. The pylorus is often seen as a distinct rounded mass of mixed echogenicity caudal to the liver, to the right of midline. Fluid filled small intestines can be seen in longitudinal and transverse section as anechoic tubes, with a central hyperechoic stripe. Peristaltic activity may be seen. If a high frequency transducer (7.5-10.0 MHz) is available, then the details of the gastric and intestinal wall can be appreciated. Five different layers are identified;
The appearance of intestine varied depending upon its contents. In majority of cases, the intestines contained mucus or feed, which appeared hyperechoic. Gas filled intestinal tract appeared as an echogenic line, creating an acoustic shadow, which prevented the intestinal tract and intestinal wall furthest from the examiner from being visualized. In cattle, apart from the cranial part of duodenum, whose wall was approximately 5mm thick, the intestinal wall was approximately 3mm thick. The cranial part of duodenum could only be identified accurately medial to gall bladder. The wall of omasum appeared as a thick echogenic line medial to duodenum. The passage of ingesta could be observed during the relaxation phase, and the intestinal contents were identified as hyperechoic. The descending colon was situated immediately adjacent to the abdominal wall and was enveloped in the greater omentum. It could be differentiated from jejunum and ileum with certainty only when it is visibly enveloped by the omentum. The loops of jejunum and ileum are usually observed in cross-section and occasionally longitudinally. They could be differentiated from duodenum because they were not surrounded by omentum and were constantly in motion.
The healthy bovine reticulum appears in ultrasound as a half moon shaped structure with smooth contour that contracts at regular intervals. When relaxed, the reticulum is situated immediately adjacent to diaphragm and ventral abdominal wall. The reticular contents are partly gaseous and thus cannot be normally be seen by ultrasound. The anterior dorsal blind sac and ventral sac of rumen and the ruminoreticular groove can be observed caudally. 3 biphasic reticular contraction cycles are observed during a 3-minute period.
Abnormal findings: Abnormal fluid distention of stomach and/or intestinal loops may be seen in cases of paralytic ileus. Foreign bodies may also be identified provided they are outlined by fluid. Gaseous distention of GI tract usually prevents a useful examination. An intussusception has a very characteristic appearance, with one section of bowel seen enclosed within a second section.
In contrast to radiological examination, ultrasound provides exact information concerning the contour of reticulum and reticular motility and is very useful technique in diagnosis of traumatic reticulo-peritonitis. In TRP, there are changes of varying severity in the contour of reticulum and in adjacent areas. The nature and extent of these changes could be described precisely and sometimes centesis of these lesions could be performed.
The deposits appear homogeneously echogenic sometimes. An echogenic capsule with a centrally located accumulation of hypoechoic fluid, which is typical ultrasound picture of an abscess, was observed repeatedly. Foreign bodies and magnets cannot be visualized by ultrasound and X-ray is the best method for its visualization. They cannot be seen on an ultrasound because reticulum contains gas and as a result visualization is limited. Ultrasound is useful for observing reticular motility and for recognizing fibrinous deposits, abscess and accumulation of fluid; however metal FB and magnets cannot be visualized. Ultrasound of reticulum is useful aid in diagnosis of TRP in cattle and supplements clinical and radiographic findings.
PHYSICS OF ULTRASOUND| MERITS| LIMITATIONS| EYE| HEART| LIVER| SPLEEN| KIDNEY| BLADDER AND PROSTRATE| PANCREAS| GI TRACT| TESTIS| REPRODUCTION AND OBSTETRICS