Intestinal Obstruction

Introduction: There are many causes of intestinal obstruction, including intessusception, neoplasia, and ingestion of foreign bodies. Obstruction may be simple or strangulated. In a simple obstruction, blood flow is not compromised, while in a strangulated obstruction it is. Obstructions are further classified as complete or partial. A complete obstruction is acute and may cause vomiting, abdominal pain, and septic shock. Partial obstruction may cause chronic diarrhea and weight loss by disrupting intestinal motility and allowing overgrowth of the normal intestinal flora. Clinical signs vary and depend on the location of the obstruction, the duration of the obstruction, and the integrity of the intestinal wall.

Pathophysiology: Dehydration, hypovolemia, electrolyte imbalances, and septicemia are dangerous potential complications of intestinal obstruction. Within 24 hours of an obstruction, dilatation occurs proximal to the obstruction as the intestinal mucosa begins to secrete fluid and electrolytes. The cause of the increase in secretion is not clear, though it has been postulated that it is due to enterotoxins from increased numbers of bacteria that accumulate in the obstructed bowel. Fluid loss, hypovolemia, and electrolyte imbalances occur as a result of vomiting and sequestration of fluid in the distended segment. Hypokalemia is often a feature, as the fluid secreted by the intestinal mucosa contains large amounts of potassium. If the obstruction is severe or persists long enough, blood flow to the intestinal wall is compromised resulting in ischemia. This results is a loss of integrity of the intestinal wall and mucosal barrier allowing bacteria from the GI lumen to gain access to the blood, causing a potentially life-threatening septicemia.

Partial obstruction of the intestine interferes with GI motility and causes stasis. A normal mechanism for controlling populations of the normal flora is peristaltic waves which keeps bacterial populations moving through the GI tract. Intestinal stasis allows the overgrowth of bacteria, which causes diarrhea by several mechanisms. For more information see Small Intestinal Bacterial Overgrowth.

Signalment: Obstruction can occur in both cats and dogs. Obstruction caused by intessusception is more common in younger animals, while obstruction caused by neoplasia is more common in older animals.

Clinical signs: Clinical signs will vary with the location and severity of the obstruction.

Gross pathology: Depends on the nature of the obstruction. There may be dilatation proximal to the obstruction. Depending on the severity and duration of the obstruction, bowel necrosis may be present.

Histopathology: Histologic lesions will depend on the nature of the obstruction and its location. In an intussusception, ischemic necrosis involves the mucosa of both segments, with congestion and edema of the submucosa, muscularis, and subserosa.

Diagnosis: Abdominal palpation combined with radiography or ultrasonography are the diagnostic techniques most often used. If plain radiographs do not allow differentiation of physiologic ileus from obstruction, contrast radiographs using barium sulfate can be considered. Exploratory surgery may be necessary.