TWENTY-FOUR: Ultrasonography of the Gastrointestinal Tract

Ultrasonography of the Gastrointestinal Tract


Fairfield T. Bain


College of Veterinary Medicine, Washington State University, Pullman, WA, USA


Ultrasonography can be applied to a significant amount of the gastrointestinal tract from the caudal pharynx and esophagus in the neck to the liver, stomach, and large and small intestines within the abdominal cavity. Depending on location and depth required to image the specific structure of interest, probes of multiple frequencies may be utilized. Superficial structures, such as the esophagus, and highest detail of intestinal surfaces may be best imaged using higher-frequency (7.5 MHz or greater) probes. Evaluation of the abdominal cavity as it pertains to the gastrointestinal tract includes evaluation of the liver, stomach, small intestine, and large intestine. The author performs the transabdominal ultrasound examination progressing in a cranial-to-caudal fashion on each side. The exam starts cranially at the third intercostal space, just caudal to the elbow, and progresses in a caudal fashion while 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, transrectal 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, where abnormal intestinal motility can be involved. Because of this, the author emphasizes the importance of serial sonographic evaluation over time to determine if anatomic changes have occurred, such as position of the colon or amount of gastric or small intestinal distension.


Esophagus


The esophagus (Figure 24.1) 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.

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Figure 24.1    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.

Stomach


The normal stomach (Figures 24.2, 24.3) is imaged adjacent to the spleen on the left side of the abdomen.

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Figure 24.2    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 tenth ICS with a curvilinear probe operating at 3.5 MHz at a depth of 18 cm.
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Figure 24.3    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 eleventh 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. Gastric distention (Figures 24.4, 24.5, 24.6) from solid ingesta, fluid, or gas is a concern when the stomach extends beyond approximately five rib spaces.

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Figure 24.4    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 fourteenth ICS with a curvilinear probe operating at 3.5 MHz at a depth of 23 cm.
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Figure 24.5    Gastric distention. Fluid content is visualized in the stomach. The cranial aspect of the stomach is obscured by the caudodorsal tip of the lung. This sonogram was obtained from the left fourteenth ICS using a curvilinear probe operating a depth of 20 cm. Image is oriented with dorsal to the left side.
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Figure 24.6    Gastric distention with fluid in a neonatal foal. The stomach is markedly distended with a width greater than that of the spleen. Milk clots (arrowhead) are visible within the gastric lumen. This sonogram was obtained from the left twelfth ICS using a curvilinear probe operating at 3.5 MHz at a depth of 6 cm.

Small Intestine


The duodenum (Figures 24.7, 24.8) 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 caudad to a point ventral to the right kidney.

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Figure 24.7    Normal duodenum, twelfth and fourteenth ICS. (A,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) twelfth and (B) fourteenth ICS using a curvilinear probe operating at 6.6 MHz at a depth of 18 cm.
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Figure 24.8    Normal duodenum, sixteenth 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 sixteenth ICS with a curvilinear probe operating at 6.6 MHz at a depth of 15 cm.

Duodenal distension (Figure 24.9) can occur with distal small intestinal obstruction, postoperative ileus, or duodenal stricture and obstruction, as well as varying degrees of thickening and distension with enteritis or proximal enteritis syndrome.

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Figure 24.9    Duodenal distension associated with postoperative ileus. The duodenum is imaged between the liver and right dorsal colon (RDC) secondary to postoperative ileus. A small pocket of hypoechoic, free peritoneal fluid is seen adjacent to the duodenum. This sonogram was obtained from the right fourteenth ICS with a curvilinear probe operating at 5.0 MHz at a depth of 15 cm.

Duodenitis (Figure 24.10) and duodenal stricture (Figure 24.11) 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, as well as monitoring medical therapy and aid in evaluation of postoperative patients that had gastrojejunostomy to relieve the gastric outflow obstruction.

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Figure 24.10    Duodenitis. This image demonstrates thick-walled duodenum (arrow) with echogenic luminal material in a 3-year-old Quarterhorse 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 twelfth ICS with a curvilinear probe operating at 5.0 MHz at a depth of 8 cm.
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Figure 24.11    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 in 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 fourteenth ICS with a curvilinear probe operating at 6.6 MHz at a depth of 12 cm.

Normal jejunum (Figure 24.12) 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.

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Figure 24.12    Normal small intestine. Normal small intestine (arrowhead) is located just medial to the spleen in the caudal left abdomen. It has a nondescript 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 distension (Figures 24.13, 24.14, 24.15, 24.16, 24.17, 24.18, 24.19, 24.20, 24.21, 24.22, 24.23) can indicate strangulating or non-strangulating obstruction, enteritis, or altered motility such as occurs with postoperative 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.

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Figure 24.13    Small intestinal volvulus in a foal. Multiple, fluid-distended, non-motile segments of small intestine are imaged in this small intestinal volvulus. This foal presented with acute, severe colic and abdominal distension. This sonogram was obtained from the ventral abdomen with a micro-convex probe operating at 6.6 MHz at a depth of 13 cm.
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Figure 24.14    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 (2.4 m) 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.
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Figure 24.15    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. Serosanguinous 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.
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Figure 24.16

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Jun 8, 2017 | Posted by in EQUINE MEDICINE | Comments Off on TWENTY-FOUR: Ultrasonography of the Gastrointestinal Tract
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