Stomach Defects

Congenital Hypertrophic Pyloric Stenosis
This malformation of the stomach is one of the more common stomach malformations.  It affects 1 in every 150 male and 1 in every 750 female infants.  In infants with this abnormality, there is a marked thickening of the pylorus, the distal sphincteric region of the stomach. The circular and, to lesser degree, muscle in the pyloric region are hypertrophied.  This results in severe narrowing (stenosis) of the pyloric canal and an obstruction to the passage of food.  Although the cause of congenital pyloric stenosis is unknown, the high incidence of the condition in both infants of monozygotic twins, suggests the involvement of genetic factors.

Anular Pancreas
This is a rare malformation that warrants description because it may cause duodenal obstruction.  The anular portion of the pancreas consists of a thin flat band of pancreatic tissue surrounding the second part of the duodenum.  An anular pancreas may cause obstruction of the duodenum shortly after birth.  In other cases, the obstruction develops later in life if inflammation or malignant disease develops in this ring-like pancreas.  Males are affected much more frequently than females.  Although other explanations have been offered, this abnormality probably results from the growth of a bifid ventral pancreatic bud around the duodenum.   The portions of the ventral bud then fuse with the dorsal bud, forming a pancreatic ring.

 

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Omphalocele
This condition occurs once in about 6000 births and results from failure of the intestines to return to the abdomen during the second stage of rotation of the midgut loop.  The hernia may consist of a single loop of bowel, or it may contain most of the intestines.  The covering of the hernial sac is the amniotic epithelium of the umbilical cord.
Faulty closure of the lateral body folds during the fourth week produces a large defect in the anterior abdominal viscera developing outside the embryo in a transparent sac of amnion.  This severe type of omphalocele, sometimes called eventration of the abdominal viscera, is often associated with exstrophy of the urinary bladder.
Normally, after the intestines return from the umbilical cord, the rectus muscles approach each other and the linea alba, closing the circular defect.  If a defect remains at this time, the omphalocele is usually small.  In both large and small omphaloceles, the protruding mass is covered by a thin transparent membrane composed of peritoneum and amnion.  One third to one half of all infants with omphalocele have other congenital malformations, e.g., malrotation, Meckel’s diverticulum, and cardiovascular defects.
 
 

Fig:  Large omphalocele in a 28-week fetus
Picture from The Developing Human. Keith L. Moore. 1982, p. 243.

Umbilical Hernia
This condition differs from an omphalocele in that the protruding mass (omentum, or loop of bowel) is covered by subcutaneous tissue and skin.  The hernia usually does not reach its maximum size until the end of the first month after birth.  It ranges in size from a marble to a grapefruit.  The defect through which the hernia occurs is the linea alba.
 
 

Fig:  structure and contents of a hernial sac
Picture from The Developing Human. Keith L. Moore. 1982, p. 243.

Meckel’s Diverticulum
This ileal diverticulum is one of the most common malformations of the digestive tract; it occurs in 2 to 4 percent of people.  This malformation is three to five times more prevalent in males than in females.  A Meckel’s diverticulum is of clinical significance because it sometimes becomes inflamed and causes symptoms mimicking appendicitis.
The wall of the diverticulum contains all layers of the ileum and may contain gastric and pancreatic tissues.  The gastric mucosa often secretes acid, producing ulceration.
A Meckel’s diverticulum represents the remnant of the proximal portion of the yolk stalk.  Typically, it appears as a finger-like pouch, about 3 to 6 cm long, arising from the antimesenteric border of the ileum 40 to 50 cm from the ileocecal junction.  A Meckel’s diverticulum may be connected to the umbilicus by a fibrous cord or a fistula.
 
 

Fig:  an ileal diverticulum
Picture from The Developing Human. Keith L. Moore. 1982, p. 246.

Hirschprung’s Disease
According to a study in the late 1940's, the constricted, nonperistaltic segment of the colon in people with this disease, lacked parasympathetic enteric ganglia. These ganglia are normally present in the gut wall. The absence of these ganglia is caused by the failure of neural crest cells to migrate into the gut wall to this segment.
Hirschsprung's disease is a digestive disorder which is caused by a single gene on chromosome 10. However, it was originally thought that this disease formed out of the interaction of numerous genes. In fact, this disease exhibits an incompletely penetrant dominant inheritance pattern. Which is to say more simply that some people who get a copy of the gene show no symptoms of the disease, while others who inherit one copy of this gene develop complications.
This disease arises very early in the development of an embryo. To ensure that a healthy gut is formed, the neural-crest cells must migrate to the colon. If these cells fail to reach their destination, a portion of the colon will develop without these crucial nerve cells. Children who lack these nerve cells in the smooth-muscle walls of the colon have interference of peristalsis. Peristalsis are the waves of muscular contractions that move solid waste through the intestinal tract. Thus, two important indicators of Hirschsprung's disease are constipation and abdominal swelling.

Imperforate Anus
Some form of imperforate anus occurs once in about 5000 births; it is more common in males.  Most anorecta malformations result from abnormal development of the urorectal septum, resulting in incomplete separation of the cloaca into urogenital and anorectal portions.

The following are low malformations of the anorectal region:

 Anal Agenesis, with or without fistula—The anal canal may end blindly and there may be an ectopic opening (ectopic anus), or fistula, that commonly opens into the perineum.  However, the fistula may open into the vulva in females or the urethra in males.  Anal agenesis with fistula results from incomplete separation of the cloaca by the urorectal septum.  It accounts for about 46 percent of cases.
 Anal Stenosis--The anus is in the normal position, but there is a narrowing of the anal canal.  This malformation is probably caused by a slight dorsal deviation of the urorectal septum as it grows caudally to fuse with the cloacal membrane.  As a result, the anal membrane (and later the anus) is small.  Sometimes, only a small probe can be inserted (the so-called microscopic anus).
 Membranous Atresia (“Covered Anus”)--The anus is in the normal position, but a thin layer of tissue separates the anal canal from the exterior.  The membrane is thin enough to bulge on straining and appears blue from the presence of meconium behind it.  This malformation is very rare and results from failure of the anal membrane to perforate at the end of the eighth week.

The following are high malformations of the anorectal region:

 Anorectal Agenesis, with or without fistula--The rectum ends well above the anal canal; this is the most common type of anorectal malformation.  Although the rectum may end blindly, there is usually a fistula to the urethra in males or the vagina in females.  Anorectal agenesis with a fistula results from incomplete separation of the cloaca by the urorectal septum.
 Rectal Atresia---The anal canal and the rectum are present, but they are separated by an atretic segment of rectum.  The cause of rectal atresia may be abnormal recanalization or defective blood supply, as discussed with atresia of the small intestine.
 

diagram of imperforate anus

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Useful sources:

Eng, Charis. The RET proto-oncogene appear to be responsible for multiple endocrine neoplasia type 2 and Hirschsprung's disease. The New England Journal of Medicine Sep 26, 1996: 335:943-952.
Worman, Scott, and Theodore G. Ganiats. Hirschsprung's disease: a cause of chronic constipation in children. American Family Physician Feb 1,1995: 51:487-496.
Romeo, Giovanni, Patrizia Ronchetto, et.al. Point mutations affecting the tyrosine kinase domain of the RET proto-oncogene in Hirschsprung's disease. Nature Jan 27,1994: 367:377-379.
Edery, Patrick, Stanislas Lyonnet, et.al. Mutations of the RET proto-oncogene in Hirschsprung's disease. Nature Jan 27, 1994: 367:378-381. (5)van Heyningen, Veronica. One gene--four syndromes. Nature Jan 27, 1994: 367:319-321.
Fackelmann, Kathy. Gutsy genetics: hunting down a gene for a children's digestive disorder. Science News Sept 11,1993: 144:174-176.

Sources:
1.  The Developing Human. 3rd ed. Keith L. Moore. W. B. Sauders Co., 1982.

Maintained by James S. Miller

Last updated January 1998

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