What are possible embryologic abnormalities?
Since some meconium and stool have passed, then anal atresia is ruled out. Around 7 weeks, the hindgut connects via a cloaca to the allantois of the umbilical region. The urorectal septum grows down to divide the rectum from the bladder and the perineum. An anal pit invaginates to contact the anal membrane of the distal rectum, which canalizes to form the anal opening. Failure to canalize results in an imperforate anus.
Another possibility in the early neonatal period is meconium ileus, a condition in which there is abnormal viscid meconium that does not easily pass and may require surgical intervention. Presence of meconium ileus may be an initial presentation of cystic fibrosis.
The most likely possibility is the presence of an aganglionic segment of rectum which causes a functional obstruction because of the lack of proper neural control of the bowel and movement of the fecal stream. This condition is known as Hirschsprung disease, seen in about 1 in 5000 live births. Bowel wall parasympathetic ganglia in submucosal and myenteric plexuses are derived from neural crest cells that migrate from the neural folds. Several genetic defects have been associated with this condition. One such defect involves a tyrosine kinase receptor encoded by the RET gene which controls neural crest cell migration. A mutation in the RET gene can lead to abnormal migration and Hirschsprung disease. Males are more often affected than females, though females are more likely to have longer segments of colon involved.
Is there a chromosomal abnormality?
In most cases, Hirschsprung disease is sporadic, but there are some familial cases, and if one child is affected, the risk is increased for subsequent children of those parents. Other malformations may be present in about 20% of cases. About 10% of cases occur in children with Down syndrome (trisomy 21).
What can be done for this condition?
Followin radiologic imaging procedures to identify involved colon, surgical exploration with biopsy to find an aganglionic segment can be performed, with excision of the affected segment and re-anastomosis of the colon. There can be "short segment" or "long segment" involvment. The extent and severity of the abnormality may determine the age at presentation, with less severe defects diagnosed later in childhood, in persons with a history of chronic constipation.
