South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
Equine Abdominal Ultrasound
Conwell R C*
BVetMed, Cert EM (IntMed), DipECEIM, MRCVS
EquiMed Referrals Ltd, UK
Abdominal ultrasound
Indications for abdominal ultrasound include weight loss, acute or chronic colic, pyrexia of
unknown origin, diarrhoea, primary hepatic or renal disease and palpation of an abnormality per
rectum.
Preparation of the patient is important to maximise image quality. Remove any dirt then clip if the
hair coat is thick, clean and rinse with alcohol before applying large amounts of gel. In thin horses
with fine haircoat, soaking with alcohol will save time and still provide a good image. Avoid
rubbing the coat and disturbing the hair and use either a spray bottle or pour the alcohol directly
onto the coat. Alcohol can be damaging to the ultrasound probe; isopropyl alcohol may be a better
alternative but the probe should still be protected by use of gel and/or a suitable cover. Horses
with coarse coats, thick skin and large amounts of subcutaneous fat will generate poorer quality
images.
A 3.5-6mHz transducer will be needed to visualise the majority of the abdomen, with a displayed
depth of 15-30 cm. The depth should be changed throughout the examination according to the
region examined. Higher frequency probes are useful for more superficial organs in thin or small
horses and have better resolution but less penetration. Smaller footprint probes give a better image
due to the smaller area of contact; linear probes, such as used for reproductive ultrasonography,
may make good skin contact more difficult. Curvilinear probes are preferred as they give optimal
resolution and enhanced repeatability. The use of different probes is likely the reason for reported
variability in normal intestinal wall thicknesses in different studies.
Adopt a systematic approach, for example start on the left hand side in the paralumbar fossa and
image dorsal to ventral and move cranially, rib space by rib space. Then scan the ventral abdomen
before moving to the right hand side and repeating as for the left side. When an abnormality is
found, scan in at least two planes to determine whether this is a true finding or artefact; artefacts
are usually only seen in one plane. Usually the dorsal aspect of the image is displayed on the right
of the screen and the ventral aspect is displayed to the left of the screen.
Imaging tips
Retroperitoneal fat can sometimes be mistaken for the spleen due to its mottled appearance and
thickness (up to 10 cm depth).
Dry ingesta, for example in the stomach, casts an acoustic shadow similar to bone.
Intraluminal gas produces a hyperechoic line with distal, acoustic shadowing and may cause
reverberation artefact.
Echogenic particles in intestinal fluid are consistent with air bubbles or ingesta.
Increased peritoneal fluid and intestinal fluid can improve the image of deeper structures as the
fluid acts to propagate the ultrasound waves.
Normal ultrasonographic appearance of the equine abdomen
Stomach
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