South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
The caecum has taenial bands orientated dorsoventrally; they contain the artery and vein within
hyperechoic fibrous tissue.
Small colon
This can be reliably imaged by transrectal ultrasound. During transabdominal ultrasound, it can be
seen in the left paralumbar fossa adjacent to the spleen. The small colon contains ingesta and gas
and has sacculations and two taenial bands, and is seen as short, sharply curving hyperechoic
lines. Wall thickness is less than 4mm, as for the other intestine. Contractions are much slower
than small intestine, at 1-3 contractions/minute.
Spleen
The spleen is finely mottled, with the distinct splenic vein. It extends from the paralumbar fossa,
adjacent to the kidney, towards ICS 8 on the left hand side and may extend across the midline
ventrally. Size varies according to breed, hydration status and position of the stomach and large
colon within the abdomen.
Lymphosarcoma is the most common splenic pathology identified ultrasonographically; the
spleen will appear enlarged with a bulging capsule and little normal parenchyma. Melanoma and
squamous cell carcinoma tend to produce images with circular, hypoechic lesions within the
splenic parenchyma.
Haematomas may be seen following trauma as clearly marginated, fluid-filled structures that
become progressively loculated and hyperechoic as the clot organises over time.
Liver
The liver has medium echogenicity in comparison to the spleen and kidneys
(spleen>liver>kidney). Only a small proportion of the liver can be imaged due to the presence of
aerated lung and gas-filled large colon covering the majority of this organ. It can be seen on the
right hand ICS 6-15 and on the left hand side ICS 6-9. Liver size varies according to age and
normal parameters for ultrasonographic size are poorly documented. It may not be possible to
image any liver on the right hand side in older horses, due to age-related atrophy. Portal veins
tend to have echogenic walls, whilst hepatic veins are anechoic vascular structures; it may be
possible to see blood flowing within the blood vessels. Bile ducts are not normally visible.
Choleliths can result in dilatation of bile ducts; the stone may not be imaged but the distended
duct is visible. The edges of the liver should be sharp and clear; an enlarged liver may be seen
with neoplastic infiltrate, acute hepatitis, hepatic lipidosis or chronic fibrosis.
Pyrexia, colic and icterus in older horses are indicative of cholangiohepatitis. Acute hepatitis is
associated with an enlarged liver, rounded lobes and reduced echogenicity; a small liver with
increased echogenicity is consistent with chronic liver disease and fibrosis. The liver may
commonly be echogenically normal and still have diffuse disease, highlighting the need for liver
biopsy to give more information. Hydatid cysts and calcifications can be incidental findings.
Kidneys
The left kidney is located in ICS 17 and the paralumber fossa, whilst the right kidney is found at
14-17 ICS. It is often not possible to see the entire kidney on one view, therefore multiple angles
and several intercostal spaces must be examined. Gas-filled bowel can obscure either kidney in
the normal horse, as well as when large colon pathology is involved; sometimes it may be
necessary to examine the horse again after several hours of fasting. Dimensions of the kidneys are
variable: right kidney 13-15 cm long, 15-18 cm wide, 5 cm thick; left kidney 15-18 cm long, 1115 cm wide, 5-6 cm thick.
The renal cortex is hypoechoic and 1-2 cm in depth and should have a smooth capsule. The
medulla is less echogenic. The renal pelvis has increased echogenicity due to fat and fibrous
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