SOURCE: The Merck Veterinary Manual
Gastrointestinal Obstruction
Gastric outflow obstruction can result from neoplasia, foreign bodies, polyps, ulcers, and gastric mucosal hypertrophy. Pyloric stenosis secondary to chronic hypertrophic gastropathy is the most common cause of gastric outflow obstruction. It is seen as a congenital lesion and is most often reported in brachycephalic breeds; it also is seen as an acquired lesion in older dogs. In dogs, there is a history of chronic intermittent vomiting and gastric distention. The etiology of pyloric stenosis is unknown, but it may be hormonally (eg, gastrin) or neurologically mediated. Positive-contrast abdominal radiographs show the obstructed stomach. Primary gastric neoplasia is uncommon. It tends to affect middle-aged to older dogs. Benign tumors include polyps and leiomyomas. Adenocarcinoma is the most common malignant form of tumor in dogs; metastasis is common, and the prognosis is poor. Therapy for gastric outflow obstruction is generally surgical. Response of chronic hypertrophic pyloric gastropathy to surgery is good to excellent.
Intestinal obstruction may be partial or complete and may be caused by foreign bodies, intussusception, gastric dilatation-volvulus, incarceration, and neoplasia. Strangulated obstructions impede blood flow to the affected intestine; simple obstructions do not. Linear foreign bodies (eg, string, pantyhose, fabric, or plastic materials) may become fixated at one end (eg, base of tongue or pylorus) or elsewhere in the GI tract. If a string becomes fixed and there is sufficient length to trail into the intestines, normal intestinal movement tends to cause a sawing or cutting motion of the string on the gut, predisposing to intestinal perforation and peritonitis. Obstruction secondary to neoplastic infiltration of the intestine is uncommon.
Pathophysiology:
Intussusception tends to develop when one segment of the intestine is hypermotile. It may also be seen with mass lesions (eg, tumors, granulomas, or scars) that become fixed and tend to get thrust into an adjacent lumen of intestine. The area involved most commonly is the ileocecocolic junction, where the smaller segment of ileum may slide into the larger lumen of the colon.
Gastroesophageal (GEI) and pylorogastric intussusceptions are more acute and severe. The prognosis for GEI is poor, with a 95% mortality rate. Clinically, vomiting and regurgitation are seen most often. With intestinal intussusceptions, vomiting, diarrhea, hematochezia or melena, anorexia, and weight loss are common clinical findings. A palpable mass is present in 50-70% of cases and is most often palpated in the cranial abdomen. Contrast radiographs or abdominal ultrasound are most useful in confirming a diagnosis. The recurrence rate for intussusception is estimated at 3-25%, and usually a different site is affected.
Distention with gas and fluid develops proximal to the obstruction. Strangulation or incarceration of bowel is seen with entrapment of intestinal loops in hernias or mesentery. Venous return is impaired although arterial supply remains intact, leading to venous congestion, anoxia, and necrosis. Loss of blood into the intestinal lumen and peritoneal cavity and the subsequent emigration of bacteria and toxins from the devitalized tissue ensues. The most common toxin-producing bacteria are Escherichia coli and clostridia.
Grossly, wall edema and hemorrhage and mucosal sloughing are apparent within 1-3 hr. After 4 hr, the affected segment of intestine is turgid, and whole blood collects within the lumen. At 8-12 hr, the affected gut appears black, distended, and elongated. Gross necrosis is evident by 20 hr.
Clinical Findings:
Clinical signs of small-intestinal obstruction may include lethargy, anorexia, vomiting, diarrhea, abdominal pain, abdominal distention, fever or subnormal body temperature, dehydration, and shock. Gaseous bowel distention develops within the initial 12-35 hr after obstruction and is followed by the loss of fluid into the intestinal lumen. Without treatment, death due to hypovolemia ensues within 3-4 days.
Upper or duodenal obstruction tends to present as frequent vomiting. In general, the closer the obstruction to the pylorus, the more severe the vomiting. Obstruction of the lower small intestine (eg, distal jejunum and ileum) is infrequently associated with vomiting. Lethargy, anorexia, weight loss, and ultimate starvation in untreated dogs lead to death within 3 wk or longer.
Intussusception may result in luminal obstruction, mucosal congestion, or infarction, depending on the length of the intussusception and the size of the intestinal loops involved. Clinical signs vary and may include vomiting, abdominal pain, and scant bloody diarrhea. In more chronic cases of intussusception, diarrhea with or without blood is seen. Intussusception is more common in young dogs (< 6-8 mo old).
In intestinal incarceration, a history of abdominal pain that rapidly progresses to hypovolemia and shock is typical. Incarceration of the affected intestine leads to bacterial proliferation within the stagnant bowel loop and to devitalization of tissue predisposing to hypovolemia and septic shock. It most commonly is seen secondary to hernia formation associated with abdominal trauma.
Diagnosis:
A careful history including information about the animal’s eating habits is important. Many animals with a history of dietary indiscretion continue that practice even after having experienced discomfort in the past. Access to string or sewing needles or missing objects (eg, toys) may be important historical facts. Examination of the oral cavity and, in cats, the base of the tongue is vital. Linear foreign bodies most often lodge at the base of the tongue in cats and at the level of the pylorus in dogs. Careful abdominal palpation examining for evidence of pain (ruptured bowel, peritonitis), organomegaly, thickened bowel loops (intussusception), and tympany (dilatation-volvulus), and a rectal examination for
Evidence of dietary indiscretion or blood (suggestive of strangulation) are important components of the physical examination.
Intussusception can be difficult to identify on abdominal palpation because the affected segments of intestine are not always turgid. Bowel loops that are incarcerated often become distended and painful.
Plain abdominal radiographs may demonstrate the presence of foreign objects, masses, obstruction, or abdominal fluid. Radiographic signs of intestinal obstruction include accumulation of fluid, gas, or ingesta proximal to the obstruction and delayed intestinal transit time. Abdominal radiographs are often diagnostic for gastric dilatation-volvulus
( Gastric Dilatation-volvulus). Gastric distention with gas and a “shelf ” of tissue causing compartmentalization is diagnostic of gastric dilatation-volvulus. Linear foreign bodies cause the small intestine to the right side of the abdomen on the ventrodorsal abdominal view is also a common radiographic indication of linear foreign bodies in cats.
The presence of free abdominal gas on survey radiographs is associated with high mortality rates. Barium contrast radiographs are best for demonstration of ileocolic intussusception. Plain radiographs are often unrewarding. Incarceration of intestine causes dilation of the affected loops, which can be seen on plain radiographs. Abdominal ultrasound is useful for diagnosing intestinal intussusception. Transverse sonographic images of intestinal intussusception often show a “target-like” appearance, a pleating or bunching up of the affected intestines. The jejunum often becomes gathered in the cranial to midventral abdomen. The presence of small, eccentrically located luminal gas bubbles (3 or more) that appear tapered at one or both ends has a high correlation with linear foreign objects in cats. Gathering of Barium-impregnated polyethylene spheres are capsules containing radiopaque plastic spheres. They are being used for the diagnosis of GI obstruction and motility disorders in dogs and cats.
Flexible endoscopic examination is useful in the identification of foreign objects, mass lesions, and ileocolic intussusception.
In animals that are systemically ill, a CBC, biochemical profile including electrolytes, and a urinalysis should be completed before therapy is initiated. Strangulation of gut causes a leukocytosis with a left shift early in the course of disease or leukopenia later and a low PCV. Initially, fluid lost into the intestinal lumen is isotonic. With time, there is an increased secretion of sodium, potassium, and albumin into the intestine. The additional loss of bicarbonate-rich secretions contributes to metabolic acidosis. Hypoproteinemia, with or without iron deficiency anemia due to GI blood loss, is common in chronic intussusception.
If abdominal fluid is detected on physical examination, abdominal radiographs, or ultrasonography, it should be aspirated and characterized as a transudate, exudate, chyle, blood, or urine. Pink to dark red peritoneal fluid may be seen with strangulation of the gut. Perforation of gut or peritonitis increases the likelihood of death.
If an obstructive lesion is documented and it cannot be resolved via endoscopy (eg, removal of a foreign object), the animal should be stabilized and an exploratory laparotomy performed. Similarly, animals with acute abdominal signs of unknown etiology, and those that continue to deteriorate clinically, should also have an exploratory laparotomy.
Treatment:
Animals that are systemically ill benefit from IV fluid therapy (eg, lactated Ringer’s or normal saline). Restoring vascular volume is vital to improve tissue perfusion. There is no difference in survival for animals undergoing small- versus large-intestinal surgery. The overall mortality rate for intestinal surgery is reported to be 12%. Large-intestinal surgery tends to be associated with longer surgery and recovery times. Animals requiring both resection and anastomosis and enterotomy are less likely to survive. Those with concurrent peritonitis reportedly have a mortality rate of up to 31%. Animals requiring more than one procedure tend to have higher mortality rates. Surgery and multiple enterotomies are necessary in most cats for the removal of linear foreign objects, yet many recover well. Peritonitis and death associated with linear foreign objects is much more common in dogs than in cats.
© 2006; Merck & Co., Inc.Whitehouse Station, NJ USA.
