CONGENITAL ABNORMALITIES OF THE GIT

What are the congenital abnormalities associated with the gastro intestinal tract?

       Depending upon the nature and timing of insult a large number of developmental abnormalities can affect the GI tract.Some of them are given here ..

Atresia,fistulae and duplications:

•      When present within the esophagus it is detected shortly after birth as it causes regurgitation.and they shoud be promptly corrected as the are incompatible for life.
• Agenesis refers to the total absence of the esophagus (rare)
• Atresia refers to the incomplete development .
• In esophageal atresia there is a thin non canalized cord replacing the segment of the esophagus and thereby causing mechanical obstruction .
• The proximal and distal parts of the esophagus are thus connected to the pharynx and the stomach respectively .
• Atresia commonly occurs near the bifurcation of the trachea and hence it can also cause fistula thus connecting the esophageal pouches to the parts of bronchus.
• Thus fistula formation causes aspiration ,perforation,suffocation , pneumonia and severe electrolyte imbalance.
• Esophageal atresia is associated with other congenital abnormalities like congenital cardiac abnormaliteis and neurologic defecits .
• Intestinal atresia is usally at the duodenum and ischaracterised by a segment of bowel lacking the lumen .
• Stenosis is an incomplete form of atresia which is charactrised by marked reduction in the caliber of the lumen and so it causes complete or the incomplete obstruction due to the fibrous thickening of the wall.
• Stenosis is most common in the esophagus and the small intestine .
• Imperforate anus is due to the failure od=f the cloacal diaphragm to involute.( most common intestinal atresia)
• Stenosis can also be caused by inflammatory scaring.
• Congenital duplication cysts may be saccular or elongated cystic masses containing smooth muscle layers  and may be found in the esophagus or small intestine.

Diaphragmatic hernia ,Omphalocele ,and Gatroschisis:

• Diaphragmatic hernia occurs when there is incompete formation of the diaphragm . This leads to the herniation of the abdominal contents into the thoracic cavity and in severe cases it may also lead to pulmonary hypoplasia.
• Omphalocele incomplete closure of the abdominal musculature  and so there is herniation into the ventral membraneous sac and is associated with other congenital abnormalities .
• Gastroschisis similar to the omphalocele but this involves all the layers form the peritonium to the skin.

Ectopia:

         These are developmental rests.

• Ectopic gastric mucosa may be present in the upper third of the mucosa (inlet patch)and if it causes acid production it leads to severe complications like dysphagia, esophagitis, barret's esophagus ,and rarely adenocarcinoma may be caused .
• Ectopic pancretic tissue may be aymptomatic or if prsent in the pyloric part of the stomach they may cause inflammation ->scaring ->complete or incomplete obstruction.
• They also mimic invasive cancer.
• Gastric heteropia ectopic gastric mucosa in the small bowel and colon and may lead to occult blood lossdue to peptic ulceration of the adjacent mucosa.

Meckel diverticulum:

• A True diverticulum is a outpoching of the alimentary tract, lined by the mucosa, and communicates with the lumen  and is lined by all the three layers of the bowel wall ( it has mucosa , sub mucosa, and mucularis propria) .The frequent one is the meckel's diverticulum .
• The Meckel diverticulum is due to the failed involution of the vittiline duct (which connects the developing gut to the yolk sac).
• It is a solitary diverticulum extending from the antimesentric side of the bowel.
• It is present in 2%of the patients ,presents at the age of 2,it is 2 inches long ,present within 2 feet of the ileocaecal valve, and occurs as twice as in males than in females  ( rule of 2's)
• This may also contain ectopic tissue.
• This leads to peptic ulcertion and leads to bleeding and abdominal pain and mimica acute appendicitis or intestinal obstruction .
• Most common site for other diverticula is sigmoid colon.

Pyloric stenosis:

       Congenital Hypertropic Pyloric Stenosis occurs with high risk in males , monozygotic twins,

turners syndrome , trisomy 18 and is associated with polygenic inheritance.

• Onset:second or third week of life as new onset regurgitation and presistant , projectile , non bilious vomiting.
• Physical examination: hyperperistalsis, ovoid, firm mass due to hypertropy of the muscularis propria thus leading to obstruction
• Edema and inflammtory changes in the mucosa and submucosa
• As a curative measure surgical splitting of the muscularisis done .(myotomy)
• Acquired pyloric stenosis is due to peptic ulceration .
• Carcinoma also causes stenosis.

Hirschsprung disease:

            Occurs in association with other congenital abnormalitis or may be isolated.

Pathogenesis:

•           It is also known as congenital aganglionic megacolon.
• Normally the enteric plexus develops from the neural crests that migrate to the bowel wall during embryogenesis.
• Here the migration of the neural crest cells from cecum to the rectum is arrested or there is immature death of the ganglionic cells .
• Distal intestinal segment lacks the auerbach myentric plexus and meissner's plexus.(aganglionosis).
• Peristalsis is absent and so there is obstruction and the proximal segment is dilated .
• There is genetic prepondrance .simple mendelian inheritance .
• Heterozygous loss of function mutation in the receptor tyrosine kinase RET
• Mutations associted with ehteric neuronal development including endothelins tyrosine kinase RET ligand glial neuratropic factor...
• Environmental and sex linked factors are also included.

Morphology:

• Done by examination of suction biopsy specimens and documenting the aganlionosis.
• Also by H&E stains and immunochemical stains .
• Rectum and sigmoid colon are affected .
• Aganglionic region is normal or contracted .
• The normal region is progressively dilated .and the proximal portionis massively distended .(megacolon)
• May even lead to rupture of the thin colonic wall.
• Intraoperative frozen section Transmural analysis gives the diagnosis.

Clinical features:

• Failure to pass meconium in the early years.and hence obstructive constipation  is caused.
• Serious complications include enterolitis,perforation , peritonitis, fluid and electrolyte imbalance .
• Treatment includes surgical resection of the distal portion and anastamosis .

Acquired megacolon is associated with chagas disease, neoplasms, ulcerative colitis ,visceral myopathy or functional diorders.