Ultrasound of Equine Abdomen

Question 1

What are the main indications for abdominal ultrasound in the horse?

Answer 1

Colic, weight loss, diarrhea, organ dysfunction, fever, hypoproteinemia

Question 2

Compare and contrast what you can see with transcutaneous vs transrectal ultrasound

Answer 2

Transcutaneous: stomach, duodenum, small intestine, cecum, large colon, liver, spleen, kidneys, bladder, gravic uterus
Transrectal: small intestine, cecum, large colon, small colon, spleen, left kidney, bladder, uterus and ovaries, aorta and associated vessels, abdominal lymph nodes, mesenteric root

*cannot image the whole abdomen in any case as the large colon is filled with gas and will block anything deep to it, and we dont have us that can penetrate that far

Question 3

What equipment is recommended for field abdominal ultrasonography?

Answer 3

2-5 MHz curvilinear probe (most common) or 1-5 MHz phased array probe
*lower frequency is the best for penetration, not quite as clear of an image

Question 4

How should you prepare a horse for an abdominal ultrasound?

Answer 4

Ideally clip the fur, but many owners wont go for this
- if you clip, use ultrasound gel, if not use alcohol (easier to clean off)

Question 5

What is the most superficial structure on the left side of the horses abdomen?

Answer 5

Spleen

Question 6

What is the equine equivalent of A fast?

Answer 6

Flash ultrasound
- localized places you look at that are most likely to be associated with colic

Question 7

What should you evaluate each organ for?

Answer 7

Location, shape, size, margins, echogenicity

Question 8

Rank these following structures from most echogenic to least echogenic: Spleen, kidney, liver

Answer 8

Kidney is hypoechoic compared to liver which is hypoechoic compared to the spleen

Question 9

Where is the liver found on a horses abdomen?

Answer 9

R: 6-15th ICS (more readily observed)
L: 6-9th ICS (not always seen)

Can only see the ventral portion (dorsal portion is blocked by the lung field)

Question 10

What happens to the location of the equine liver with age?

Answer 10

The right lobe undergoes atrophy and the whole liver shifts further to the right

Question 11

How does the liver appear on ultrasound?

Answer 11

Mottled appearance
- sharp margins
- branching vascular pattern
- no gall bladder
- bile ducts not seen unless they are distended

Question 12

Where can you see the spleen on a horse?

Answer 12

Left ICS 8 to paralumbar fossa
- sometimes crosses ventral midline (variable)
- superficial

Question 13

What does the spleen look like on ultrasound?

Answer 13

• more hyperechoic than the liver
  -can see stomach nearby (will see gastrosplenic vein nearby)
  -usually has a granular homogenous appearance with few blood vessels

Question 14

Where are the kidneys located in a horse?

Answer 14

Right- rostral paralumbar fossa to ICS 16, nothing superficial to this
Left- deep to the spleen, paralumbar fossa and dorsal ICS 16-17 (farther caudal than right kidney)

Question 15

What is the significance of the space between the spleen and the kidney on the left side of the horse?

Answer 15

Nephrosplenic space- common site of colon entrapment (potential space)

Question 16

What should you look for when analyzing the kidneys on ultrasound?

Answer 16

Size, echogenicity, corticomedullary distinction

Question 17

What should you assess when analyzing the GI tract of horses?

Answer 17

Diameter
- depends on section of GI tract
- helpful with SI lesions (cant see other wall of colon due to gas), should be less than 5-6 cm, should be constantly moving

Motility

Wall thickness
- serosa (hyperechoic), muscularis (hypoechoic), submucosa (hyperechoic), mucosa (hypoechoic)
- often hard to see details of all 4 layers (unless using higher frequency probe or looking at stomach wall)
-should be 3-4 mm in thickness (except stomach which can be up to 7.5 mm)

Location

Contents

Question 18

Where is the jejunum best visualized?

Answer 18

In the left inguinal area (most commonly)
- but not abnormal to see it in any other place of the abdomen

Question 19

Where do you usually find the duodenum on ultrasound?

Answer 19

Cranial to the cranial pole of the right kidney OR deep to the liver

Question 20

Where is the large colon and cecum located? What about specifically the right dorsal colon?

Answer 20

Large colon: sits on floor of the abdomen on both sides
Cecum: sits over the large colon on the right side
Right dorsal colon: sits deep to the liver on the right (duodenum sits in between the liver and right dorsal colon)

Question 21

What is the main cause of right dorsal colitis?

Answer 21

NSAID toxicity
- will see thickened wall of the right dorsal kidney

Question 22

Describe the appearance of cecum and large colon on ultrasound?

Answer 22

They will look the same
- large diameter, gas filled, sacculations (except left dorsal colon)
-normal wall thickness <3 mm
-peristalsis: 2-6 contractions per minute

Question 23

Where is the stomach found in a horse? What is its normal appearance on ultrasound?

Answer 23

On the left side of the abdomen between the 8th an d13th ICS deep to the spleen
-normal wall thickness is <7.5 mm, with very little motility

Question 24

How can you determine if there is a strangulating obstruction on ultrasound?

Answer 24

Multiple loops of distended small intestine, sedimentation may be present
- these horses need to be referred ASAP- horses cant vomit and this is an emergency!

Question 25

What are signs of enteritis on ultrasound?

Answer 25

Fluid filled loops of small intestine, more motility than strangulating obstruction, can see wall thickening
- needs to be referred, will be reflexing a lot

Question 26

What may you see with displacement/volvulus?

Answer 26

Thick and edematous wall of the large colon

Question 27

What is often observed on ultrasound in cases of nephrosplenic entrapment?

Answer 27

Ventrally displaced spleen, with a caudally displaced and gas distended small colon
*wont be able to see the kidney!

Question 28

Where is peritonitis often observed on ultrasound?

Answer 28

Central midline
- often will see excess abdominal fluid, thickened intestinal loops

Question 29

What does blood look like on ultrasound?

Answer 29

Swirling mottled appearance