The different anatomical parts of the gastrointestinal tract can be recognized.
The oesophagus
The abdominal part of the oesophagus can be visualized with longitudinal scans. lying inferior to the diaphragm and anterior to the aorta. With transverse scans, the oesophagus is seen behind the left lobe of the liver.
The stomach
When empty, the fundus of the stomach will be star-shaped and easily identified. The body of the stomach will be seen on transverse scanning, Just anterior to the pancreas. If there is confusion, give the patient one or two glasses of water to distend the stomach.
Small and large bowel
The appearance of the bowel varies greatly depending upon the degree of fullness, the liquid content and the number of faeces and gas. Normal peristalsis may be seen on scanning. If the bowel is full of fluid, there will be characteristic mobile echoes. Peristalsis is usually seen in the small bowel but not always in the colon.
With ultrasound, the wall of the intestine is seen as two layers: an external hypogenic layer (the muscle) and an internal hyperechogenic layer (the mucosa in contact with the gas in the bowel). The muscle wall is seldom more than 3mm thick, depending on the part of the bowel and the degree of filling.
The gas within the bowel is hyperechogenic and may produce reverberation artefacts and an acoustic shadow posteriorly, while fluid within the bowel is echo-free or may produce some echoes due to faeces.
The normal movements due to respiration should be recognized and differentiated from peristalsis.
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