Rana Bozorgmanesh* *Hagyard Equine Medical Institute, Lexington, KY, USA Ultrasonography can be performed to evaluate a significant portion of the gastrointestinal tract from the caudal pharynx and esophagus in the neck, to the stomach, and large and small intestines within the abdominal cavity. Depending on location and depth, probes of multiple frequencies may be utilized to image the specific structure of interest. Higher frequency (7.5 mHz or greater) probes can be used to image superficial structures, such as the esophagus, or to obtain the highest detail of intestinal surfaces (if reasonably superficial). Evaluation of the abdominal cavity as it pertains to the gastrointestinal tract includes evaluation of the stomach, small intestine, and large intestine. Typically, the author performs the trans-abdominal ultrasound examination in a cranial-to-caudal fashion on each side. However, in situations such as a violently painful colic case or a colicky horse with a high heart rate, the most pertinent structures are often evaluated first, such as the stomach to identify severe distention and immediate need for nasogastric intubation. The more systematic examination starts cranially at the third intercostal space, just caudal to the elbow, and progresses caudally scanning dorsal to ventral in each intercostal space from the diaphragm margin ventrad. Cranially on the left side, the liver is visible adjacent to the spleen. Moving caudally, the stomach is visualized adjacent to the spleen. The stomach is evaluated for contents and size. The normal stomach in the adult horse usually extends over four to five intercostal spaces. Normal small intestine has minimal visible structure. It may be visible with variable motility just ventromedial to the spleen on the left side. The colon is visible ventromedial to the spleen on the left side. On the right side, the large colon is visible in the cranial abdomen. Progressing caudally, the liver is visible ventral to the margin of the lung fields over most of the mid-abdomen. Horses in their mid-teens and older may have atrophy of the liver and it may not be readily visualized with ultrasound. The duodenum is visible ventromedial to the liver from the twelfth intercostal space to just ventral to the right kidney. The right dorsal colon is ventromedial. Ventral-medial to the duodenum is the right dorsal colon. The cecum will be visible in the right paralumbar fossa and extends ventrally along the costal arch and can be distinguished by its lateral vasculature. On occasion, trans-rectal ultrasonographic examination may be useful in further characterizing abdominal masses, rectal masses, or intestinal surfaces. The gastrointestinal anatomy within the abdominal cavity can be dynamic, especially in colic cases where abnormal intestinal motility and distention can be involved. As such, the author emphasizes the importance of serial ultrasonographic evaluations over time to determine if changes have occurred such as position of the colon or amount of gastric or small intestinal distension. The esophagus (Figure 23.1) can be imaged from just caudal to the pharynx in the upper neck on the left side along most of its course to the distal neck. It is located just dorsal to the trachea and ventral to the jugular vein and carotid artery. The muscularis appears hypoechoic, whereas the lumen appears echogenic. Figure 23.1 Normal esophagus. The normal esophagus is demonstrated by the arrowheads. The trachea is in the bottom left corner of the image. The jugular vein is noted by the large arrow and the carotid artery by the small arrow. This sonogram was obtained from the jugular groove, middle third of the neck, using a linear probe operating at 12 MHz at a depth of 5 cm. The normal stomach (Figures 23.2 and 23.3) is imaged adjacent to the spleen on the left side of the abdomen. Figure 23.2 Spleen–stomach relationship. This image demonstrates the normal appearance of the stomach adjacent to the spleen. The normal, feed containing stomach should appear as an echogenic curved line (arrow) against the medial surface of the spleen. The splenic portal vein (arrowhead) is seen along the medial aspect of the spleen. This sonogram was obtained from the left 10th ICS with a curvilinear probe operating at 3.5 MHz at a depth of 18 cm. Figure 23.3 Gastric fold. This image shows the normal appearance of stomach adjacent to the spleen in a horse fasted for gastroscopy. A gastric fold (arrowhead) is visible on the surface of the stomach. This sonogram was obtained from the left 11th ICS using a curvilinear probe operating at 3.5 MHz at a depth of 18 cm. Gastric impaction should be considered in animals with a prolonged clinical history of inappetence, mild colic signs, and sonographic evidence of solid gastric luminal content visible over more than five intercostal spaces. These cases can also present with more acute colic signs and when passage of a nasogastric tube is attempted, resistance is met at the cardia or just beyond. Gastric distention (Figures 23.4, 23.5, 23.6, and 23.7) from solid ingesta, fluid, or gas is a concern when the stomach extends beyond approximately five rib spaces. Figure 23.4 Gastric distention. This image demonstrates a fluid filled, distended stomach (short arrow) in an adult horse. Solid material ventrally (arrowhead) creates an acoustic shadow. A gas-fluid interface (long arrow) is present dorsally. This sonogram was obtained from the left 14th ICS with a curvilinear probe operating at 3.5 MHz at a depth of 23 cm. Figure 23.5 Gastric distention. Fluid content is visualized in the stomach. The cranial aspect of the stomach is obscurred by the caudodorsal tip of the lung. This sonogram was obtained from the left 14th ICS using a curvilinear probe operating a depth of 20 cm. Figure 23.6 Gastric distension. Fluid content is visualized in the stomach. The caudal aspect of the stomach is adjacent to the cranial edge of the spleen. This sonogram was obtained from the left 14th ICS using a curvilinear probe operating a depth of 28 cm. Figure 23.7 Gastric distension with stomach tube in place. Fluid content is visualized in the stomach. An acoustic shadow from the indwelling stomach tube is present at the caudal margin of the stomach. This sonogram was obtained from the left 14th ICS using a curvilinear probe operating a depth of 28 cm. The duodenum (Figures 23.8 and 23.9) can be imaged along its course on the right side. It is first seen cranially as it appears between the left liver lobe and the right dorsal colon, and then progresses caudal to a point ventral to the right kidney. Figure 23.8 Normal duodenum, 12th and 14th ICS. (A) and (B) These images show normal duodenum. The cranial aspect of the duodenum is visible between the left liver lobe and the right dorsal colon. The echogenic material is luminal content within the duodenum. These sonograms were obtained from the right ((A) 12th and (B) 14th ICS using a curvilinear probe operating at 6.6 MHz at a depth of 18cm. Figure 23.9 Normal duodenum, 16th ICS. This image shows normal duodenum ventral to the right kidney and ventromedial to the right dorsal colon. This sonogram was obtained from the right 16th ICS with a curvilinear probe operating at 6.6 MHz at a depth of 15 cm. Duodenal distension (Figure 23.10) can occur with distal small intestinal obstruction, post-operative ileus, or duodenal stricture and obstruction, as well as varying degrees of thickening and distension with enteritis or proximal enteritis syndrome. Figure 23.10 Duodenal distension associated with post operative ileus. The duodenum is imaged between the liver and right dorsal colon (RDC) secondary to post-operative ileus. A small pocket of hypoechoic, free peritoneal fluid is seen adjacent to the duodenum. This sonogram was obtained from the right 14th ICS with a curvilinear probe operating at 5.0 MHz at a depth of 15 cm. Duodenitis (Figure 23.11) and duodenal stricture (Figure 23.12) can produce gastric outflow obstruction in foals. The thickened segment of duodenum can often be imaged along its course on the right side of the abdomen. Ultrasound can be useful in making the initial diagnosis (which is typically then confirmed gastroscopically), as well as monitoring medical therapy and aid in evaluation of post-operative patients that had gastrojejunostomy to relieve the gastric outflow obstruction. Figure 23.11 Duodenitis. This image demonstrates thick-walled duodenum (arrow) with echogenic luminal material in a 3-year-old Quarter Horse mare that presented with colic and gastric reflux. Salmonella spp. was isolated from the gastric fluid suggesting it may have been an etiology for the duodenitis. Normal duodenal wall thickness in an adult horse is ≤ 3 mm This sonogram was obtained from the right 12th ICS with a curvilinear probe operating at 5.0 MHz at a depth of 8cm. Figure 23.12 Duodenal stricture. This image demonstrates duodenal thickening and stricture producing clinical signs consistent with gastric outflow obstruction in a 6-month-old Hanovarian filly. Duodenal stricture is more common in foals than adult horses and may be secondary to ulceration of the duodenum and pyloric region. Ulceration can be multifactorial in cause, but may be associated with previous rotavirus infection. This sonogram was obtained from the right 14th ICS with a curvilinear probe operating at 6.6 MHz at a depth of 12 cm. Normal jejunum (Figure 23.13) usually has a nondescript appearance on ultrasound. It is usually visible just ventral and medial to the spleen in the caudal left abdomen around the level of the costal arch. Figure 23.13 Normal small intestine. Normal small intestine (arrowhead) is located just medial to the spleen in the caudal left abdomen. It has a non-descript appearance. Wall thickness should not exceed 3 mm. This sonogram was obtained from the caudal left abdomen with a curvilinear probe operating at 6.6 MHz at a depth of 15 cm. Small intestinal distention (Figures 23.14, 23.15, 23.16, 23.17, 23.18, 23.19, 23.20, 23.21, 23.22, 23.23, 23.24, 23.25, and 23.26) can indicate strangulating or non-strangulating obstruction, enteritis, or altered motility such as occurs with post-operative ileus. Clinical history, severity of clinical signs, and occasionally other diagnostic aids such as abdominocentesis are required to differentiate between these types of lesions prior to confirmation by exploratory surgery. Figure 23.14 Post-operative ileus in a post-foaling mare with peritonitis following repair of a uterine tear. There are multiple dilated, non-motile loops of small intestine. The mare refluxed for several days until motility eventually normalized. This sonogram was obtained from the ventral abdomen using a curvilinear probe operating a depth of 29 cm. Figure 23.15 Small intestinal volvulus in a yearling. Multiple, fluid-distended, non-motile segments of small intestine are visualized in a yearling presenting for severe abdominal pain of several hours duration. Eight feet of non-viable small intestine were resected at surgery. This image was obtained from the ventral abdomen with a curvilinear probe operating at 3.5 Mhz at a depth of 15 cm. Figure 23.16 Mesenteric defect. Fluid-distended, poorly motile, thick walled small intestine (arrows) in the left ventral abdomen is imaged in a yearling colt with acute severe colic. The walls of the small intestine measured greater than the normal 3 mm. Serosanginous peritoneal fluid was observed on abdominocentesis. Multiple segments of thick-walled, red and purple small intestine associated with a mesenteric defect were found at surgery. This sonogram was obtained from the left abdomen with a curvilinear probe operating at 3.5 MHz at a depth of 15 cm. Figure 23.17 Small intestinal strangulation. This image from the patient in Figure 23.15
23
Ultrasonography of the Gastrointestinal Tract
Esophagus
Stomach
Small Intestine
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
