Intestinal obstruction is the most common abdominal emergency in the neonatal period. It is almost always the result of a congenital anomaly of the gastrointestinal tract, which must be rectified surgically if the infant is to survive. Mortality in surgically untreated patients is close to 100%, and the rate of survival is closely related to the time of surgical intervention (Hajivassiliou 2003). The most common clinical findings are abdominal distension, vomiting, and sometimes failure to pass meconium, depending on the level of the obstruction. These findings usually prompt the clinician to consult the radiologist, who must answer three major questions: Is the obstruction present? What is the location of the obstruction? What is the aetiology? The most valuable means of determining whether or not obstruction is present is the plain abdominal radiograph. Plain radiographs are often diagnostic. When not diagnostic, they may provide important clues suggesting the subsequent most valuable diagnostic procedure (Singleton et al. 1977).
Knowledge of the many variations in both the distribution and quantity of intestinal air in infants is useful in the interpretation of pathologic findings. In a healthy neonate, air can usually be identified in the stomach within minutes after birth, and reaches the proximal portion of the small bowel during the first 6 h of life. By 6-12 h the entire small bowel usually contains air, and after 12-24 h normal neonates show rectosigmoid air in a plain abdominal radiograph.
When an intestinal obstruction is present, since air proceeds distally in the gastrointestinal tract until stopped at the obstruction, an abdominal radiograph will show dilated air-filled loops proximal to the obstruction and no air distal to it. The number of dilated loops depends on the site of obstruction: the lower the obstruction, the greater the number of dilated loops. Having established that an intestinal obstruction is present, the radiologist should still determine the location of the obstruction and, if possible, the etiology. In order to arrive at a useable differential diagnostic list of possible etiologies, neonatal obstructions can be classified as high or low obstruction. High or upper intestinal obstructions are those that occur proximal to the mid-ileum and include obstructions involving the stomach, duodenum, jejunum, and proximal ileum. Obstructions that involve the distal ileum or colon are called low intestinal obstructions. The distinction between high and low obstruction is also critical since children with high obstructions usually need little or no radiologic evaluation after plain radiograph, and the specific diagnosis is made in the operating room. Newborns with low obstructions need a contrast enema, which usually provides a specific diagnosis and may be therapeutic (Buonomo 1997). In general, plain radiographs in neonates with high obstruction reveal one, two, or a few dilated air-filled bowel loops, depending on the level of the obstruction, while radiographs in low obstructions show multiple dilated air-filled bowel loops.
Disorders of the intestinal tract in the neonatal period usually present with abdominal distension and dilatation of the bowel. However, not all intestinal dilatations represent obstruction. Infants with medical disorders such as sepsis, electrolyte imbalance or necrotizing enterocolitis may present ileus characterized by uniform dilatation of the bowel to the level of the rectum. Also, infants on continuous positive airways pressure may swallow an excessive amount of air and exhibit important intestinal dilatation. This dilatation must be distinguished from mechanical obstruction, because the treatment is completely different. The differentiation between these two categories can usually be made on the basis of clinical history, laboratory tests, and appropriate radiographs (Hernanz-Schulman 1999).
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