Louisiana State University, Veterinary Clinical Sciences, Baton Rouge, LA, USA
Radiography allows an overview of the abdomen while ultrasonography does not. A short cut to ultrasound in a vomiting animal could lead to misdiagnosis of a disease that could be readily identified radiographically. Therefore, radiography and ultrasonography should be considered complimentary diagnostic tests. Barium studies still have importance in assessing animals with chronic gastrointestinal obstructions.
Take Home Message of This Lecture
1. A three-view radiographic procedure is required in every vomiting dog or cat
a. Right and left lateral and a VD image
b. Left lateral places gas in the pylorus and duodenum to find foreign material
2. Wooden spoon compression
a. Compress the bowel with a wooden spoon to separate loops of jejunum from one another so that foreign material, linear foreign bodies and corrugations can be detected without superimposition
3. Barium studies and ultrasound should only be performed after 1 and 2 are performed
Ileus is a failure of intestinal contents to be transported and is recognized radiographically by the presence of dilated bowel segments. Survey abdominal radiographs should always be performed in vomiting animals with vomiting. Ultrasound alone in such instances does not allow a global view of the abdomen, is much more time consuming and non-gastrointestinal causes of the dog’s clinical signs as well as any secondary abnormalities may be overlooked. The radiographic appearance of ileus is dependent on its duration, location, and degree of obstruction. Acute or very proximal obstructions may show little intestinal dilation radiographically whereas chronic or more distally located ones will show more generalized dilation of the small intestines. The two major types of ileus are obstructive (mechanical) and functional. Obstructive ileus may be partial or complete.
Dogs and cats with partial obstructions tend to have a more chronic course of intermittent vomiting and diarrhea. Common causes include foreign bodies and strictures. Fasted (>12 hours) or anorectic animals should not have small bowel segments containing granular material resembling that of food content radiographically. Granular or more opaque small bowel contents may be detected in partial obstructions. The intestines in such cases may be mildly dilated (1–1.5 times the width of the second lumbar vertebral body) proximal to the obstruction or may even be of normal diameter. Because partial obstructions may be more difficult to diagnose radiographically than complete obstructions, complementary imaging procedures such as barium studies or ultrasound are often necessary for the diagnosis. Repeat radiographic examination has great diagnostic value when abnormal intestinal content is identified. If granular content is seen in the small intestine of an animal that is vomiting or anorectic for more than 24 hours, obstruction should be considered likely. If the same finding of focal granular luminal content is identified on follow-up radiographs, even if intestinal dilation is not evident, in a vomiting animal, the chances of obstruction are high and sonography or exploratory surgery is indicated. Ultrasonography is highly recommended in older animals to screen for intestinal masses prior to exploratory laparotomy.
More severe dilation, usually with air, is seen in complete obstructions. The location of the obstruction can be either intraluminal (foreign bodies), extraluminal (adhesions, herniation, intussusceptions), or intramural (neoplastic wall infiltrations, granulomas). Dilation (1.5–2 times the width of the body of L2) is seen proximal to the site of obstruction and the segments distal to it usually appear empty and contracted. Due to this, the jejunal segments appear to have many varied diameters, some very dilated, others empty or small. This is called a “mixed population.” This is due to the continued peristaltic activity in the distal segments. The dilated segments are often referred to as “sentinel loops.” Proximal duodenal or pyloric obstructions may show no radiographic abnormalities. Twenty-four (24) hours following a gastric outflow obstruction, the animal has vomited out the intestinal contents and the intestinal content moves to the colon. Abdominal radiographs may show no abnormalities or gastric distention. Moreover, the entire gastrointestinal tract may actually appear completely empty after some hours due to recurrent vomiting.
The most common difficulty in diagnosing complete obstructions is in trying to differentiate small from large bowel when the colon is dilated and especially gas filled. It is recommended in such instances to perform a small volume barium enema in order to identify the colon and distinguish it from the small intestinal segments that may or may not be dilated. When the abdomen appears normal radiographically in a vomiting animal, either a barium study or an ultrasound examination should be the next diagnostic procedure.
Another form of ileus that can be detected is a generalized and uniform mild intestinal dilation due to lack of peristaltic activity. This is known as adynamic, functional, or paralytic ileus and results from an inhibition of bowel motility. Functional ileus results in obstruction since the intestinal contents pool in the dependent areas of the gastrointestinal tract. Radiographically the gastrointestinal tract appears mildly dilated, can have a mixed content with some gas- and some fluid-filled intestines and colon have generalized fluid or gas filling. The distribution of the intestines in the abdomen is regular. Gas is often present in the stomach. Typically, granular ingesta in the stomach and bowel is not identified. The intestines appear to have a uniform diameter. Animals with this pattern typically have clinical signs of both vomiting and diarrhea. Such an adynamic intestinal pattern can be due to the administration of pharmaceutical agents such as parasympatholytics and sedatives. Other causes are peritonitis, blunt abdominal trauma, electrolyte imbalance, and enteritis of various causes.
Complicated forms of ileus include bowel perforation with peritonitis, free air in the abdominal cavity, bowel ischemia due to thromboembolism, intussusception, or volvulus at the root of the mesentery. Linear foreign bodies can also lead to a complicated form of ileus. The presence of pneumoperitoneum together with abdominal effusion on an abdominal radiograph should alert the clinician that bowel perforation has occurred. The detection of free intraabdominal air may require the use of ventrodorsal horizontal beam radiography with the patient in left lateral recumbency. Free air can be detected just under the right abdominal wall and lateral to the duodenum. Volvulus or mesenteric thromboembolism is recognized by the presence of generalized, severely dilated and air-filled jejunal segments. Linear foreign bodies produce characteristic changes on abdominal radiographs in both cats and dogs. The small intestinal loops appear convoluted and gathered or clumped together at one site, usually in the mid-right abdomen and intraluminal gas bubbles appear asymmetrical and irregularly shaped.
Complications of Obstructions
Gastrointestinal perforation affects the peritoneum of dogs and cats. Due to this, radiographic and sonographic features of perforation are characteristic of peritoneal disease. Clinical signs include fever, dyspnea, inappetence, vomiting, abdominal pain, and possible diarrhea. Causes of perforation of the gastrointestinal tract in dogs and cats include foreign body perforation, perforating ulcer either due to benign or malignant diseases, non-steroidal anti-inflammatory therapy, bullet wound perforation, surgical dehiscence, intussusception, gastric dilatation volvulus.
Free gas in the peritoneal space usually occurs with a perforated intestinal wall. However, chronic erosions of the wall due to neoplasm or chronic foreign body may be walled off and gas may not be evident radiographically. Free gas in the absence of recent laparotomy, trauma, or abdominal perforation usually indicates intestinal perforation as the source. Presence of free air is in most all cases a surgical emergency. Rupture of the stomach usually leads to large amounts of air while if in the small intestine, the amount is smaller. Radiographic signs of pneumoperitoneum include loss of serosal detail as well as increased visualization of serosal margins due to outlining with gas. Horizontal beam radiography is indicated for suspicion of free gas when only small volumes are present. Free peritoneal air will tend to accumulate adjacent to the diaphragm, have triangular shapes, and may collect adjacent to the ribs and between the liver lobes. Large volumes of free gas can be more difficult to recognize radiographically than small volumes as they are so generalized over the abdomen they go unnoticed. The loss of serosal detail in the presence of free air is usually due to peritonitis secondary to the perforation. Radiographically, unless an intestinal mass or a radiolucent foreign body is identified, the site of intestinal perforation often is not identifiable.