Review Question - QID 214459

This patient has signs of obstruction (abdominal distention, bilious vomit, and no stool in the rectal vault) and failure to pass meconium. The abdominal radiograph shows non-specific dilated small bowel loops, most consistent with meconium ileus secondary to cystic fibrosis.

Cystic fibrosis (CF) may present as meconium ileus (unable to pass meconium in the first 24-48 hours after birth). Due to mutations in the CFTR gene (ion channel protein that conducts chloride ions across epithelial cell membranes), meconium in patients with CF becomes thickened due to improper ion transport leading to increased viscosity and decreased water content. Patients present with signs of a distal small bowel obstruction (e.g., bilious vomit, abdominal distention, and no passing of meconium). Diagnosis of meconium ileus is typically made with an abdominal radiograph, which demonstrates dilated small bowel loops and a positive Neuhauser sign (soap bubble appearance in the distal ileum due to air mixed with meconium). Patients are typically treated with an enema with a contrast agent, but more severe cases (intestinal perforation or volvulus) require surgery. Later in life, patients with CF develop obstructive lung disease, impaired pancreatic and biliary secretion, and infertility.

Figure/Illustration A is an abdominal radiograph demonstrating meconium ileus. The findings are non-specific and include dilated bowel loops (yellow arrow) proximal to the impaction, typically with a paucity of air-fluid levels (red arrow).

Incorrect Answers:
Answer 2: Duodenal atresia is the result of failed recanalization of the duodenum during development. Patients present with signs of obstruction, delayed meconium passage, and vomiting. Duodenal atresia is associated with Down syndrome and abdominal radiograph demonstrates the double bubble sign.

Answer 3: Hirschsprung disease is a condition characterized by an aganglionic colon segment, which fails to relax causing functional intestinal obstruction. Patients typically present with failure to pass meconium, but rectal exam would demonstrate a tight anal sphincter and explosive discharge of stool and gas. Abdominal radiographs in Hirschsprung disease demonstrate dilated colon (not small bowel) immediately proximal to the aganglionic region.

Answer 4: Midgut volvulus is characterized as the twisting of a loop of bowel on its mesentery causing intestinal obstruction. Patients present with signs of obstruction (abdominal pain, distention, and bilious vomiting) or signs of bowel ischemia (tachycardia, hypotension, hematochezia, and peritonitis). Neonates with intestinal malrotation are at risk of developing midgut volvulus, which will demonstrate the corkscrew sign (spiral appearance of the distal duodenum and proximal jejunum) on fluoroscopy (abdominal radiographs are typically normal).

Answer 5: Pyloric stenosis is characterized by hypertrophy of the pyloric sphincter in the first few months of life. Patients typically present with a gastric outlet obstruction between 3-5 weeks of life. On physical exam an enlarged, nontender pylorus may be palpable in the epigastrium and abdominal ultrasound demonstrates an elongated and thickened pylorus.

Bullet Summary:
The first sign of cystic fibrosis may be meconium ileus, which is the inability to pass meconium in the first 24-48 hours and appears as dilated small bowel loops on abdominal radiograph.