Key practice points

The physical examination can usually differentiate between ileus and obstruction. Ileus will present with absent or rare bowel sounds, whereas the physical examination in obstruction will reveal hyperactive, high-pitched (tinkling) bowel sounds.

Additional testing

Laboratory studies

Blood tests aid in establishing the cause of mechanical obstruction only in rare cases related to inflammation, infection, or neoplasm; in contrast, laboratory studies often indicate the cause of ileus. Abnormal electrolyte (including calcium, phosphate, and magnesium), blood urea nitrogen, or creatinine values support a clinical impression of dehydration. Leukocytosis may be present with inflammation or infection. Measurement of arterial blood gases may be necessary to evaluate the acid–base balance. With an ischemic or infarcted bowel, elevations in amylase, alkaline phosphatase, creatine phosphokinase, aspartate and alanine aminotransferase, and lactate dehydrogenase may be evident, although these enzymes also increase with hepatic and pancreaticobiliary disease.

Plain radiographic studies

Plain radiographs should be the initial structural studies performed on patients with suspected ileus or obstruction. Chest radiography can detect pneumonia, evaluate cardiorespiratory status, and detect free subdiaphragmatic air, whereas supine and upright abdominal plain films show intra-abdominal gas distribution. With complete occlusion of the small intestine, the lumen is widely distended and the valvulae conniventes are observed to span the lumenal air column; in addition, the colon empties within 12–24 h and no colonic air is radiographically visible. Upright or decubitus views commonly demonstrate air–fluid levels in a stepladder configuration.

With colonic obstruction, the colon proximal to the blockage dilates and the characteristic incomplete and scalloped indentations of the haustra are visible. With advanced strangulation, the bowel wall becomes edematous, exhibiting a thumbprint pattern on radiographs, and air in the intestinal wall, portal vein, and peritoneal cavity may be observed.

In ileus, lumenal dilation may be generalized or it may only manifest adjacent to an inflammatory site, producing a sentinel loop, as in appendicitis or pancreatitis. With concurrent peritonitis, the bowel wall may thicken. Colonic gas usually is more prominent in ileus than with small intestinal obstruction. Pure colonic dilation, most pronounced in the cecum, is the defining feature of acute colonic pseudo-obstruction. Stepladder air–fluid levels may be observed with either ileus or obstruction, but they are more well defined and longer with obstruction. A string-of-beads pattern of the air–fluid interfaces is most suggestive of high-grade obstruction of the small intestine. A diffusely hazy pattern with central localization of bowel loops is characteristic of ascites.

Additional structural studies

Computed tomographic scanning is used to define the site of obstruction and to exclude selected underlying disease processes (i.e. inflammation versus neoplasm). Conversely, ultrasound is generally not useful because of the obscuring effects of intralumenal gas. Upper endoscopy is useful with suspected esophageal, gastric, or duodenal lesions and offers the additional capability of therapeutic dilation of any stricture. Push enteroscopy provides similar diagnostic and therapeutic capabilities to the proximal jejunum. Angiography or magnetic resonance angiography may be useful for patients with suspected mesenteric ischemia and infarction.

Functional studies

Functional testing of gut motility may be considered for patients with prolonged ileus or suspected chronic intestinal pseudo-obstruction. Gastric emptying scintigraphy may document gastroparesis, whereas esophageal or gastroduodenal manometry may show the characteristic hypomotility pattern of visceral myopathy or the random, intense bursts of contractions in visceral neuropathy.

Differential diagnosis

Acute ileus, chronic pseudo-obstruction, and mechanical obstruction have numerous causes (Table 8.1).

Acute ileus

Several conditions have been associated with the development of acute ileus. Ileus is the normal physiological response to laparotomy. Gastric and small intestinal motility recover in the first postoperative day, whereas colonic contractions return in 3–5 days. Postoperative ileus beyond that time is considered pathological and warrants a search for surgical complications. Other intra-abdominal causes of acute ileus include abdominal trauma and inflammatory gut disorders. Noninflammatory conditions (radiation damage and mesenteric ischemia) and retroperitoneal disorders can also produce acute ileus. Extra-abdominal causes of ileus include reflex inhibition of gut motility by craniotomy, fractures, myocardial infarction, heart surgery, pneumonia, pulmonary embolus, and burns. Medications may inhibit motor activity, as may metabolic abnormalities.

Chronic intestinal pseudo-obstruction

Chronic intestinal pseudo-obstruction is a consequence of a variety of conditions. Chronic idiopathic pseudo-obstruction often presents after a viral prodrome, suggesting an infectious etiology. Hereditary conditions such as familial visceral myopathies and neuropathies produce pseudo-obstruction at early ages. In addition to gastroparesis, long-standing, poorly controlled diabetes mellitus may disrupt motor function in the small intestine. Rheumatological disorders and some endocrinopathies can lead to chronic pseudo-obstruction. Neuromuscular diseases chronically disrupt motor activity. In selected geographic locations, Chagas disease represents an infectious cause of pseudo-obstruction that occurs after exposure to Trypanosoma cruzi. Viral pseudo-obstruction in immunosuppressed patients has been reported as a consequence of infection with cytomegalovirus and other agents. Pheochromocytoma produces chronic intestinal hypomotility, probably because of the motor inhibitory effects of circulating catecholamines. Chronic intestinal pseudo-obstruction can be a paraneoplastic manifestation of small cell lung carcinoma and, less commonly, other malignancies. Paraneoplastic pseudo-obstruction results from malignant invasion of the celiac axis or, alternatively, from plasma cell infiltration of the myenteric plexus, leading to the loss of enteric neural function.

Table 8.1 Causes of ileus and obstruction

Acute ileus

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