A. Causes

1. Duodenal Atresia
   1. Trisomy 21
   2. Double Bubble on abdominal radiograph
   3. Bilious Vomiting
2. Small Bowel Atresia
   1. Air-fluid levels on abdominal radiograph
   2. Treat with resection
3. Imperforate Anus
   1. Most common cause of obstruction
   2. Blind pouch above or below levator ani
   3. Massive distension
4. Meconium Ileus
   1. Impaction, Small Bowel Obstruction
   2. Can often dissolve obstruction with N-acetyl cysteine
5. Hirschprung Disease (see below)
6. Pyloric Stenosis [1]
   1. Gradual Obstruction with gastric hypertrophy
   2. Projectile vomiting
   3. Hypokalemia with metabolic alkalosis
   4. Myenteric neurons innervating circular muscle of pyloric sphincter lack nitric oxide
   5. This defect appears to be due to lack of inducible nitric oxide synthetase
   6. Treated with Pyloromyotomy
   7. May also be caused by heterotopic pancreatic tissue in pyloric smooth muscle [3]
7. Intussusception
   1. Meckel's Diverticulum
   2. Polyp
   3. Intestinal obstruction with rectal blood, "currant-jelly stool"
   4. Reduction often by barium enema
8. Gastroschisis
   1. Anterior abdominal wall defect leads to exposed bowel
   2. Occurs lateral to umbilical cord
   3. Chemical (amniotic fluid) peritonitis, bacterial invasion
   4. Intestinal atresia at hernia ring
9. Hernia
   1. Inguinal - indirect: Failure of resorption of processes vaginalis to tunica vaginalis
   2. Umbilical
   3. Incarceration or strangulation

B. Hirschprung Disease (HD) [1]

1. Etiology
   1. Absent myenteric plexi in distal colon and rectum
   2. Aganglionic gut loses tonic neural inhibition and remains contracted
   3. Absence of neurons containing vasoactive intestinal polypeptide and nitric oxide
   4. Occurs due to failure of neural crest cells to migrate to distal colon
2. Genetics
   1. Congenital disease with autosomal recessive (AR) and autosomal dominant (AD) forms
   2. Some patients with AD form have mutations in RET gene [2]
   3. RET mutations also cause MEN-II syndrome; screen for this in patients with HD
   4. Many patients with AR form have mutations in gene for endothelin B receptor
3. Related Syndromes
   1. Waardenburg Syndrome - HD, white eyebrows and lashes, white forelock
   2. Santos Syndrome - HD with renal agenesis, polydactyly, hypertelorism, deafness
4. Symptoms of HD
   1. Malnutrition
   2. Enterocolitis
   3. Abdominal distension and pain
5. Diagnosis
   1. Barium Enema
   2. Intestinal biopsy looking for nerve plexi (which are absent)
6. Treated by colonic resection and ostomy

C. Symptoms and Signs of Intestinal Obstruction

1. Maternal Hydramnios
2. Bilious Vomiting
3. Projectile, non-bilious vomiting
4. Abdominal Distension
5. Failure to pass Meconium Stool
6. Failure to Thrive

D. Evaluation

1. Careful history and physical examination
2. Rule out perforation is critical initial goal
3. Complete blood count and electrolytes
4. Blood cultures if bacteremia is possible
5. Chest and/or Abdominal Radiograph
   1. Air-fluid levels
   2. Free air under diaphragm
6. Surgical correction is nearly always required

References

1. Goyal RK and Hirano I. 1996. NEJM. 334(17):1106
2. Eng C. 1996. NEJM. 335(13):943
3. Lund DP and Compton CC. 1999. NEJM. 341(9):679 (Case Record)