Microcolon in newborn infants with intestinal obstruction. Its correlation with the level and time of onset of obstruction.

Abstract

Microcolon is the radiologic finding of a colon of tiny caliber on barium-enema examination of newborn infants with intestinal obstruction. It signifies only that the obstruction is above the colon. Barium-enema studies have shown that many infants with intestinal obstruction above the colon do not have “microcolon.” This finding led to a review of the size of the colon in newborn patients with all levels of intestinal obstruction. The colon caliber has been correlated with both the level and the time of onset of the fetal intestinal obstruction. Factors Normally Dilating the Fetal Colon The fetal gastrointestinal tract is a site of active work throughout the last two trimesters of pregnancy (1). The fetus actively swallows amnion, and this fluid load, estimated at several liters a day, mixes with gastric juice, bile, and the desquamated intestinal cells and succus entericus to form meconium, the feces of the fetus. Normally, the mixture becomes less fluid in the lower small bowel as amnion is absorbed; the fetal colon is distended by and filled with the meconium prior to birth. It is not known with certainty but is generally thought that meconium defecation in utero is not “normal” and suggests some fetal distress (1). Since each of the above factors can be included or excluded by intestinal obstruction at an appropriate level, the infants born with intestinal obstruction constitute an experimental model. It is possible, by studying the colon size, to evaluate the factors leading not only to “microcolon” but to a normal-size colon in a newborn infant (Fig. 1). Level and Onset of Obstruction Related to Colon Caliber at Birth (Table I) A. Esophageal Obstruction: Esophageal atresia is considered a first trimester embryologic anomaly. As such, it is found in conjunction with other malformations: imperforate anus, duodenal atresia, absence of the radii, renal anomalies, and the like. The patients born with esophageal atresia and no tracheoesophageal fistula have been unable to swallow amnion. In such cases the barium-enema examination shows a colon of normal caliber (Fig. 2), thus excluding swallowed amnion as a significant factor in the dilating forces of the fetal colon. B. Duodenal Obstruction: It is in the duodenum that the older theories of intestinal atresia emphasized the “failure of normal recanalization following a solid core stage” (8). Although this concept was previously applied to all levels of fetal intestinal obstruction, the condition was never shown in the jejunum or ileum of embryos. Duodenal atresia is still felt to be a first trimester embryologic anomaly. Like esophageal atresia it is associated with other abnormalities: mongolism (Down's syndrome), imperforate anus, renal anomalies. Usually the obstruction (commonly a diaphragm-type atresia) is below the ampulla of Vater.