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MECONIUM ILEUS

INTRODUCTION

Meconium ileus is a neonatal condition characterized by a distal mechanical small bowel obstruction from thick viscous meconium. Although mainly described in patients with cystic fibrosis (CF), meconium ileus has also been described independent of CF. Mutations to the cystic fibrosis transmembrane conductance regulator (CFTR) gene in CF affect chloride transport, resulting in thick, protein-concentrated meconium that causes a mechanical obstruction at or prior to birth. The pathogenesis of meconium ileus in non-CF patients is not well understood. Approximately 13% to 17% of newborn infants with CF will present with meconium ileus.

CLINICAL MANIFESTATIONS

Meconium ileus can be subdivided into simple and complex. Newborns with simple meconium ileus present with intestinal obstruction characterized by abdominal distention, bilious emesis, and failure to pass meconium. The infant may have visible peristalsis through the abdominal wall and palpable “doughy” bowel loops on abdominal exam. In addition to these findings, newborns with complex meconium ileus may have intestinal perforation, atresia, or volvulus. Neonates with complex meconium ileus may have tenderness, erythema of the abdominal wall, and systemic signs of illness on physical examination. Infants with in utero intestinal perforation and meconium cyst formation may have a palpable abdominal mass without significant tenderness.

DIAGNOSIS

Supine and left-lateral decubitus abdominal radiographs are the initial diagnostic test of choice in most neonates with suspected bowel obstruction. Infants with simple meconium ileus will have multiple fluid-filled loops of intestine with a “soap-bubble” or “ground-glass” appearance of the intestine demonstrated on radiographs, caused by the mixture of thick meconium and gas (Fig. 398-1). Intestinal obstruction typically occurs at the terminal ileum. The proximal intestine is often distended, with a thickened intestinal wall. A calcified, cystic abdominal mass visible on plain radiograph is highly suspicious for complicated meconium ileus with in utero perforation. The differential diagnosis includes other causes of neonatal obstruction or perforation, including atresia, malrotation, meconium plug, and Hirschsprung disease.

Figure 398-1

Abdominal radiograph of a newborn with meconium ileus. Arrow indicates the “soap-bubble” appearance of the meconium in the terminal ileum.

TREATMENT

Neonates with suspected meconium ileus should be managed like any infant with intestinal obstruction. The infant should not be fed, a nasogastric or orogastric tube should be placed, and intravenous fluid should be provided to establish euvolemia. Neonates with evidence of perforation or peritonitis should proceed to laparotomy following resuscitation. If an initial laparotomy is not required, additional workup and possible nonoperative therapy is appropriate.

Hyperosmolar water-soluble contrast enema with a combination of diatrizoate meglumine and diatrizoate sodium (ie, Gastrograffin) is useful for both diagnosis and treatment. Infants with simple meconium ileus will have a patent, unused microcolon. Reflux of contrast into the distal ileum will often demonstrate ...

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