Learning objectives: be able to quickly collect accurate information with your ultrasound, and how to use this information to make treatment decisions for colic cases. Technical considerations: Similar to the complete abdominal ultrasound evaluation, a large curvilinear (2–6 MHz) transducer is required. Horses with a sport clip frequently don’t require additional clipping. In horses with thick hair, consider finding the pre-defined windows by soaking the hair in alcohol and deciding whether clipping specific areas is needed.

The fast, localized sonogram of the horse (FLASH) is a sonographic protocol developed to identify key locations to obtain important information rapidly in cases of colic.¹ The FLASH is relatively straightforward and easy to learn and as such readily applicable in equine practice. It does require image recognition of the classic abnormalities, and this session provides an opportunity to review these classic and less classic abnormal images.

Duodenal Window

• Where? Right dorsal 17th–16th intercostal spaces
• What? Duodenum ventral to the right kidney
• Normal: duodenum present, filled with content, normal motility (can be affected by sedation)
• Abnormal: fluid-filled non-motile duodenum
• Suggestive of anterior enteritis but a proximal obstructive lesion is possible

Right Mid Window

• Where? Right mid-14th–12th intercostal spaces
• What? Tip of the liver, right dorsal colon and right ventral colon
• Normal: Tip of the liver, right dorsal colon and right ventral colon
• Abnormal: Presence of a dilated blood vessel (>1 cm)
• Right dorsal displacement

Ventral Window

• Where? Cranial ventral abdomen
• What? Ventral colon
• Normal: Wall thickness <3 mm, small amount of anechoic fluid
• Abnormal: Wall thickness >9 mm, medium to large amount of anechoic fluid, any amount of echoic fluid
• Colon torsion

It’s important to note that other diseases can cause large colon thickening such as inflammatory bowel disease or lymphoma, however, these cases typically don’t present with acute colic and as such patient selection is important when applying this rule. Typically, the thickened colon wall of a colonic torsion has an edematous corrugated appearance, whereas inflammatory bowel disease and lymphoma cause cellular infiltration of the submucosa. This difference is however not always appreciable.

Look for Small Intestine in the Inguinal Area

• Normal: Motile filled with content, wall thickness < 3 mm
• Abnormal: Amotile, distended (> 6 cm), thick walled (> 3 mm)
• Small intestinal lesion

It’s not possible to distinguish anterior enteritis from surgical small intestinal lesion in 100% of the cases. Data from the original FLASH paper found distended small intestine to have good sensitivity and specificity for the need for surgery. Dilated loops of small intestine were seen in eight horses with a strangulating lesion but also one horse with proximal enteritis.¹ Findings in favor of proximal enteritis include distended loops with decreased but some motility. Findings in favor of a surgical lesion include a population of distended small intestine with a normal wall thickness and another population of small intestinal loops with a thickened wall, representing the strangulating portion.² However, horses with proximal enteritis can have thickened small intestinal wall and the enteritis can be segmental. As such, the sonographic findings should be used in conjunction with clinical and clinicopathologic data to make the choice for surgical versus medical management in small intestinal lesions.

Gastric Window

• Where? Left mid-10th–15th intercostal spaces.
• What? Stomach and spleen.
• Normal: Stomach covering 5–6 intercostal spaces, containing food and gas.
• Abnormal: Large fluid-filled stomach.
• Gastric intubation needed. If large content-filled stomach: consider gastric impaction.

Nephrosplenic Window

• Where? Left paralumbar fossa and 17th–16th intercostal spaces
• What? Left kidney and spleen
• Normal: kidney adjacent to the spleen, normal rounded dorsal border of the spleen
• Abnormal: kidney obscured by gas shadow from gas within the colon, horizontal dorsal border of the spleen created by gas shadow of gas within the colon.
• Nephrosplenic entrapment

The inability to image the left kidney is suggestive of nephrosplenic entrapment but can also be seen with other displacements. In addition, false positive results have also been reported.^1,3

In conclusion, the FLASH provides critical information that assist decision-making in colic cases. However, the findings should be interpreted in conjunction with findings of the clinical exam, transrectal palpation, blood work and results of the abdominocentesis to form a complete picture.

References

1.  Busoni V, Busscher V De, Lopez D, Verwilghen D, Cassart D. Evaluation of a protocol for fast localised abdominal sonography of horses (FLASH) admitted for colic. Vet J. 2011;188(1):77–82.

2.  le Jeune S, Whitcomb MB. Ultrasound of the equine acute abdomen. Vet Clin North Am Equine Pract. 2014;30(2):353–381.

3.  Beccati F, Pepe M, Gialletti R, Cercone M, Bazzica C, Nannarone S. Is there a statistical correlation between ultrasonographic findings and definitive diagnosis in horses with acute abdominal pain? Equine Vet J Suppl. 2011;39:98–105.