South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
The stomach is seen on the left hand side, ventral to the lung and dorsal to the costochondral
junction, at the level of the shoulder. It is normal for the stomach to extend over 3 intercostal
spaces in horses (usually from ICS 9-11) and it has a characteristic smooth, curvilinear echo
adjacent to the spleen and splenic vein, with colon ventrally. The thickness of the stomach wall
can vary from 4mm up to 7.5mm in adult horses; reduced wall thickness has been reported when
the stomach is distended and also post feeding. The wall thickness may be greatest post
gastroscopy as the stomach contracts and deflates. Motility is not evident. Fluid distension of the
stomach (reflux) will give a horizontal fluid/gas line.
The appearance of the stomach can change following gastroscopy and air-insufflation, and
therefore possibly also following nasogastric intubation. An undulating stomach wall is a
common finding post gastroscopy, with more distinct gastric wall folding (of the mucosa and
submucosa) sometimes seen, most distinctly 2-4 hours post gastroscopy. Rugal folds may also be
seen in horses undergoing food restriction.
Ultrasonography of the stomach is useful to identify dilatation, impaction and neoplasia.
Identification of the stomach extending over more than 3 intercostal spaces suggests gastric
distension, either due to gastric impaction or reflux. The enlarged stomach may also be imaged
adjacent to the left lateral wall as the spleen is pushed caudally and ventrally.
Gastric neoplasia is most commonly imaged as a mural mass, rather than seen gastroscopically.
There may be increased peritoneal fluid and involvement of the adjacent organs, particularly the
spleen.
Ponies differ in that the stomach can be imaged over a greater number of intercostal spaces than
in horses (average 5 intercostal spaces, sometimes up to 8).
Small intestine
Small intestine can be imaged transabdominally and transrectally. Normal small intestinal wall
thickness is less than 4 mm, with a diameter of less than 5 cm and 6-15 contractions per minute.
Normal wall thickness does vary between studies according to the probe used and the stage of
contraction/distension at which measurements are taken. The contents may be fluid (hypoechoic),
ingesta (hyperechoic, heterogenous) or gas (hyperechoic with gas shadowing).
The duodenum can be seen reliably on the right hand side of the abdomen, in intercostal spaces
(ICS) 16-17 ventral to the caudal pole of the right kidney, and medial to the liver in ICS 14-16.
The duodenum is commonly seen to fill with ingesta and then collapse.
The jejunum varies in location; whilst some studies suggest that jejunum is not consistently
found, reasonably reliable locations include the left inguinal region, deep to the spleen in ICS 1216 in the gastrosplenic region and dorsal to the left colon in the left ventral caudal region. Small
intestine is seen in the cranioventral abdomen in only 10% of normal horses. Fasting increases the
likelihood of finding small intestine in the cranioventral abdomen (due to emptying of the colon
and caecum).
The normal small intestine has 5 layers visible on ultrasound, however these are not always easily
identified in the normal horse during transabdominal ultrasound, due to the poor resolution from
lower frequency probes. The 5 layers are serosa (hyperechoic), muscularis (hypoechoic),
submucosa (hyperechoic), mucosa (hypoechoic) and the mucosal/ingesta interface (hyperechoic).
The ileum has a 7 layer appearance due to the additional muscular layer and can be imaged
transrectally, medial to the caecum.
The small intestine should be assessed in terms of location, wall thickness, diameter, motility and
contents. Disease processes that can be identified ultrasonographically include simple and
strangulating obstructions, infiltrative/inflammatory bowel disease, intraluminal masses and
enteritis. Ultrasonography is more sensitive than rectal palpation for detection of distended small
intestine, particularly in the early stages of a proximal obstruction. Distended loops will fall to the
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