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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.
Partial Obstructions
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.
Complete Obstructions
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. 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.
Functional Ileus
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 ileus
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.
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