Description
Introduction The Fast Localized Abdominal Sonogram of Horses (FLASH) is the initial sonographic examination performed in horses with acute colic and is used to assess whether surgical intervention is indicated. It is important to understanding the limitations of the FLASH examination and when a complete ultrasound examination is indicated. In horses with chronic colic, a complete abdominal ultrasound examination is the examination of choice. The complete ultrasound examination is also indicated in the acute, less severe colic, when the aetiology of the colic and the decision for surgical intervention, is not clear from the FLASH examination. This results in a complete examination of all the imageable portions of the gastrointestinal tract, resulting in the ability to diagnose a wide variety of gastrointestinal abnormalities. Abnormal Findings in Horses with Colic Herniation/Displacement Displacement of the gastrointestinal viscera into the thoracic cavity through a diaphragmatic hernia can usually be diagnosed ultrasonographically. The rent in the diaphragm may be visualized as the abdominal viscera come over it into the thoracic cavity. The muscular portion of the diaphragm is thickened and retracted. The gastrointestinal viscera should be evaluated for wall thickening, distention and abnormal motility and other signs of compromise. Nephrosplenic ligament entrapment Diagnosis of a nephrosplenic ligament entrapment ultrasonographically is based upon the inability to visualize the left kidney and the visualization of ingesta and/or gas filled large bowel in the dorsal aspect of the caudal left side of the abdomen. The spleen is ventrally displaced. The dorsal portion of the visible spleen has a straight horizontal dorsal border extending from the paralumbar fossa to the 10-12th intercostal space, at which point the colon is no longer visible due to the overlying lung. Right dorsal displacement The sonographic detection of enlarged colonic mesenteric blood vessels above the right costochondral junction is indicative of a right dorsal displacement. This may also be imaged in horses with an 180o large colon volvulus. Lack of visualization of the duodenum and liver is often noticed in horses with a right dorsal displacement. A right dorsal displacement, a 180 o large colon volvulus or both were 32.5 times more likely to be found at surgery when a colonic mesenteric vessel was detected ultrasonographically on the right side of the abdomen above the costochondral junction. Large colon torsion Marked thickening of the large colon wall is consistent with a diagnosis of large colon torsion. A colonic wall thickness > 9 mm is an accurate predictor of a large colon torsion in horses with surgical colic localized to the large colon. Nonsacculated large colon in the left ventral abdomen in horses with abdominal pain is indicative of large colon volvulus. The speed of decreases in the bowel wall thickness post-surgery correlates with outcome. Intussusceptions Intussusceptions have a characteristic target or bull’s eye sign. There are many different possible sonographic appearances for the intussusception, depending upon which portion of the intussusception is being imaged. Often fibrin and fluid is imaged between the two loops of intestine. Ileal intussusceptions are more common in young horses and may be imaged rectally or transcutaneously. Intussusceptions in adult horses usually involve the ileum and/ or large bowel. The majority of intussusceptions imaged in adult horses are imaged from the right side of the abdomen because the cecum or right ventral colon is involved. Strangulating small intestinal lesions Distended, fluid-filled small intestine is aboral to a strangulated portion of small intestine. The strangulated small intestine usually has thickened, edematous, hypoechoic walls with little or no peristaltic activity. Two populations of small intestine, one collapsed with normal wall thickness and the other with a thickened wall, turgid appearance and little or no motility is consistent with a strangulating lesion. In older horses with a strangulating lipoma, the lipoma itself is rarely imaged. Complete volvulus of the small intestine may also occur, similarly affecting the entire small intestine. Distended small intestine with thickened walls is most frequently detected ventrally. Thickening of the wall of the strangulated loops of small intestine is usually less echoic than wall thickening associated with a cellular infiltration, fibrosis or hypertrophy of the intestinal wall, usually seen in nonstrangulating lesions. Surgical intervention was indicated in one study of horses with colic when edematous small intestine was imaged in conjunction with decreased small intestinal motility. Strangulating lesions of the small colon Increased wall thickness and intestinal distention have been reported in several horses with strangulating lesions in the small colon imaged with transrectal ultrasonography. Transabdominal ultrasonography has been useful in diagnosing strangulating lesions in the small colon in miniature horses. Impaction An impaction can often be imaged from the right flank or side of the abdomen with cecal or right dorsal colon impactions. Small colon impactions may be imaged transrectally, when scanning the caudal abdomen, as echogenic intraluminal masses. Cecal impactions can also be imaged transrectally when palpable. Impactions can only be imaged sonographically when the impacted portion of the large colon or cecum is adjacent to the body wall or fluid is interposed between the affected portion of the intestine and the body wall. The impaction appears as a round to oval amotile distended viscus, often measuring 20 - 30 cm or more, lacking any visible sacculations. The bowel wall may be normal thickness or may be thicker than normal and there is a large acoustic shadow cast from the impacted ingesta adjacent to the colonic mucosa. Enteritis/Duodenitis Fluid distension of the small intestine with increased peristalsis indicates developing enteritis. The intestinal wall may be thickened, edematous and more hypoechoic than normal. Shreds of intestinal mucosa may be imaged in the lumen. Fluid distention of the duodenum and stomach can also be imaged with anterior enteritis, as well as with other more distal obstructions. The lack of motility in these intestinal segments is consistent with an ileus. The thickness and echogenicity of the bowel wall are an indication of the degree of bowel wall involvement. Proximal duodenitis/ anterior enteritis may have an associated cholangiohepatitis with elevated biliary enzymes. Necrotizing enterocolitis Sonography can identify intramural gas (pneumatosis intestinalis), portal venous gas, intraperitoneal gas, bowel wall thickening, and bowel wall perfusion in horses with necrotizing enterocolitis. Thinning of the bowel wall and lack of bowel wall perfusion are indicative of nonviable intestine and possible impending perforation. Gastritis/gastric ulceration Irregular thickening of the gastric wall with prominent rugal folds may be detected in some horses with gastritis. Gastric ulcers cannot usually be imaged ultrasonographically. Gastric distention Fluid, gas and ingesta can all be imaged sonographically in the stomach in horses with gastric distention. Gastric impaction The distended stomach is less circular than normal, with hyperechoic ingesta or anechoic to hypoechoic fluid in the lumen of the stomach. The sonographic appearance of a gastric impaction is a markedly enlarged gastric echo extending over 7 or more intercostal spaces on the left side of the abdomen. There may also be ventral and caudal displacement of the spleen. Gastric rupture Gas in the mesentery adjacent to the stomach or stuck in the fibrin present within the peritoneal fluid and/or a pneumoperitoneum is suggestive of a gastric rupture. Fibrin and particulate matter may be imaged floating within the free peritoneal fluid. Peritoneal fluid Normally only a small amount of anechoic peritoneal fluid is imaged. A large amount of anechoic fluid is consistent with ascites (rare in horses), peritonitis or neoplasia. Hypoechoic or echogenic, flocculent, composite fluid, fibrin and/or adhesions between the intestine and the abdominal wall is compatible with peritonitis. Free gas echoes, pneumoperitoneum and/or particulate echogenic debris are consistent with a ruptured viscus. Homogeneous, hypoechoic to echogenic swirling fluid is imaged in horses with hemoperitoneum.