Health Tips and Tricks

CLINICAL BACKGROUND

A wide spectrum of pathophysiologic mechanisms may come into play when ileus or obstruction involve the small and large intestines. The most life-threatening abnormality is ischemic necrosis that occurs as a result of complicated obstruction. When blood flow is compromised, the most vulnerable bowel layer, the mucosa, becomes nonviable. This disrupts the normal functions of absorption and secretion, but more important, it destroys the protective barrier against intralumenal microorganisms. Lethal bacteria and toxins traverse the intestinal wall, causing peritonitis, abscesses, toxemia, and sepsis. The process is accelerated if transmural necrosis and perforation occur. Because of the high mortality rate associated with this complication, prevention is the best clinical plan. Early recognition is not sufficient, because it is often too late to intervene when clinical signs become apparent. Anticipation of this lethal complication and early surgical intervention should be adopted as the therapeutic strategy in many, if not most cases of obstruction of the small and large intestine.
Because of intestinal stasis in progressive obstruction, the normal gram-positive aerobic flora of the small intestine are replaced by anaerobic and gram-negative flora. If ileus or obstruction is incomplete, the result
may be maldigestion due to bacterial overgrowth. If the stasis is complete, especially if accompanied by ischemia, severe infectious complications may occur. The same complications may occur as a result of surgical procedures involving enterotomy, making preoperative administration of antibiotics an important therapeutic intervention.
As a result of ileus or obstruction, the normal processes of fluid and electrolyte transport are altered. In the small bowel, secretory processes are enhanced, resulting in accumulation of fluid and electrolytes in the lumen. Normal gastric, biliary, and pancreatic secretions also accumulate, causing vomiting. Oral intake is frequently reduced or absent. Treatment involves correction of fluid and electrolyte losses, restoration of acid-base balance, and provision for maintenance fluid and electrolyte requirements through intravenous infusion.
In addition to fluid in the lumen, gas accumulates largely from swallowed air but also from bacterial metabolism of nutrients. This produces marked dilation of the bowel and abdominal distention, causing abdominal pain, respiratory embarrassment, and changes in intestinal and colonic motility. Initially in obstruction of the small intestine the peristaltic reflex is activated, causing stimulation of motor activity and abnormal motor patterns proximal to the obstruction and inhibition of motor activity distal to the obstruction. As tension in the wall increases, inhibitory intestinointestinal reflexes are activated, causing progressive inhibition in the gut proximal to the obstruction. Decompression of the dilated bowel should be accomplished by means of intermittent nasogastric aspiration in essentially all cases of ileus and obstruction to relieve symptoms of pressure, vomiting, and pain and to reduce the risk for perforation and many of the pathophysiologic problems described previously.
For both ileus and obstruction, the differential diagnosis is varied and lengthy. Recognition and management of ileus involves recognition and management of the underlying cause of the problem. Surgical therapy must be avoided unless associated emergency disorders exist. However, in most instances of obstruction, the problem is anatomic and mechanical; definitive therapy necessitates surgical intervention in most instances. There are some important exceptions when surgical intervention should be avoided or alternative treatments are preferred. When obstruction is partial, recurrent, and due to prior multiple surgical procedural adhesions, it is usually wise to avoid another operation. Untwisting or decompression of volvulus, laser vaporization of tumors, and pneumatic dilation of strictures are a few of the treatments that can be accomplished with endoscopy. Radiologic and other nonsurgical approaches can provide other therapeutic alternatives.
The laboratory can play an important role in establishing the underlying problem in many cases of ileus, but radiologic techniques are the most useful tools in the differentiation of ileus from obstruction and in identifying the level and the cause of obstruction.

PLAIN ABDOMINAL RADIOGRAPHS

When clinical suspicion of intestinal obstruction or ileus arises, plain abdominal radiographs (anteroposterior, upright, and supine) are the first radiologic modality to perform. In the normal, unobstructed condition, there is usually some gas in the stomach and colon; in the colon, the gas may or may not be mixed with feces. A small amount of gas may be present in the small intestine of children; however, in adults there is almost none.
In several situations, the radiographic gas patterns on plain radiographs are so characteristic of intestinal obstruction that no further contrast study or other radiologic modality is needed to make a diagnosis. Complete obstruction of the small intestine
Figure 4-1. Complete obstruction of the small intestine. Multiple loops of the dilated small intestine are present on this upright abdominal radiograph without noticeable colonic gas in this acutely ill, middle-aged woman. The findings suggest mechanical obstruction of the small intestine. Numerous surgical clips testify to previous operations. Multiple adhesions causing obstruction were found in the distal jejunum at operation.



mesenteric vascular accident with compromised vascular flow resulting in functional obstruction
Figure 4-2. Mesenteric ischemia (ileus). Several loops of small intestine located on the left side of the abdomen appear irregular and distended with gas bubbles. A large amount of gas is present in the rest of the small intestine. A small amount of air is present in the colon. Ischemic enteritis was suspected because of these findings, and the patient underwent an operation. A loop of necrotic jejunum measuring 80 cm in length was resected.

and
Figure 4-3A. Mesenteric ischemia (ileus). This patient was admitted to the emergency department because of the sudden onset of abdominal pain, distention, weakness, and low-grade fever. A: On the first plain radiograph of the abdomen, the right colon and transverse colon are distended with gas and demonstrate a scalloped margin (arrowheads) and thickened edematous haustra. Acute ischemic enterocolitis was suspected. After 2 days of observation, the general condition deteriorated and more abdominal distention was observed clinically. B: The follow-up radiograph reveals similar but more pronounced findings. An emergency operation confirmed the diagnosis of thromboembolic occlusion of the ileocolic branches of the superior mesenteric artery, resulting in necrosis of the distal 35 cm of ileum and proximal colon, including the right four fifths of the transverse colon.

 volvulus of the sigmoid colon (Fig. 4-4) or the cecum (Fig. 4-5), and toxic megacolon (Fig. 4-6) are some conditions with characteristic radiographic findings. High-grade mechanical obstruction of the postbulb or proximal duodenum may show a double bubble sign, which also is diagnostic (Fig. 4-7).

ADDITIONAL RADIOLOGIC FINDINGS THAT SUGGEST SPECIFIC DIAGNOSES

Sometimes radiographic findings in addition to the intestinal gas pattern help one to make specific diagnoses on plain radiographs. Examples are air in the biliary tree in gallstone obstruction (Fig. 4-8), free intraperitoneal air or a calcified appendicolith associated with dilated ileum in perforated appendicitis (Fig. 4-9, presence of calcifications in the pancreas associated with dilation of the bowel from acute exacerbation of pancreatitis causing functional obstruction (Fig. 4-10), or presence of hernia containing a closed loop of intestine (Fig. 4-11).

STUDIES IN ADDITION TO ROUTINE PLAIN ABDOMINAL RADIOGRAPHS

There are situations in which routine plain anteroposterior supine and upright radiographs of the abdomen are inconclusive and additional studies are needed to establish the underlying diagnosis (Fig. 4-12). Barium contrast studies and abdominal imaging studies, including ultrasonography, computed tomography, and magnetic resonance imaging, may be helpful to establish a preoperative diagnosis (Fig. 4-13). Endoscopy is not ordinarily recommended in this setting because insufflating air into an already dilated bowel may worsen the situation. An exception exists when the procedure can be therapeutic by reducing massive colonic dilation from ileus or relieving obstruction. An example of the latter includes decompression of sigmoid volvulus. It should be emphasized that in most situations, differentiating obstruction from ileus is the important decision that governs therapy. In these cases it is neither useful nor desirable to perform multiple diagnostic tests that would delay appropriate surgical therapy.

DIFFERENTIATION OF ILEUS AND BOWEL OBSTRUCTION BY MEANS OF COMPARING THE DIAMETERS OF THE SMALL BOWEL AND TRANSVERSE COLON

If the loops of small intestine appear equal to or larger than the transverse colon, either right-sided colonic obstruction or small-intestinal obstruction should be considered. A barium enema examination that includes the ileocecal valve is necessary to search for a right hemicolonic lesion (see Fig. 4-5). A small intestine series may be obtained (Fig. 4-14, Fig. 4-15 and Fig. 4-16) for obstruction of the small intestine, but enteroclysis is the examination of choice, particularly for postoperative patients.
Radiologic signs of distal colonic obstruction on plain radiographs of abdomen are dilation of the colon with an empty rectum, marked retention of either solid or liquid stools (Fig. 4-17), and multiple air-fluid levels in the dilated proximal colon (Fig. 4-18). The small intestine may or may not be dilated, but the loops of small bowel proximal to the transverse colon retain a diameter smaller than that of the transverse colon (Fig. 4-19). This picture can be confused with that of paralytic ileus, but the issue can be resolved with performance of a barium enema examination or colonoscopy.
Differentiation of ileus from mechanical obstruction is usually but not always possible with plain abdominal radiographs (Fig. 4-20). In ileus, both the colon and small bowel are dilated, and the diameter of the colon is greater than that of the ileum. In such cases, administration of contrast medium is essential to determine the presence or absence of obstruction. Before administering barium into the upper gastrointestinal tract, it is critical to establish that the level of obstruction is not in the colon. If barium is given orally and reaches an obstruction in the colon, it stops at that point. Water is extracted, and the barium forms a cement-like concretion that is difficult and hazardous to remove surgically. If there is any question about colonic obstruction, a barium enema examination should be performed first.