Atresia, Fistulae, and Duplications• Atresia, fistulae, and duplications may occur in anypart of the GI tract.• Esophageal Atresia: cause regurgitation duringfeeding. These must be corrected promptly, sincethey are incompatible with life.• A thin, noncanalized cord replaces a segment ofesophagus, causing a mechanical obstruction.Proximal and distal blind pouches connect to thepharynx and stomach, respectively.•
Atresia occurs most commonly at or near thetracheal bifurcation and is usually associated witha fistula connecting the upper or lower esophagealpouches to a bronchus or the trachea.Fistulae can lead to aspiration, suffocation,pneumonia, and severe fluid and electrolyteimbalances.Esophageal atresia is associated with congenitalheart defects, genitourinary malformations, andneurologic disease.
.Intestinal atresia is less common than esophagealatresia but frequently involves the duodenumand is characterized by a segment of bowel lackinga lumen.Imperforate anus, the most common form ofcongenital intestinal atresia, is due to a failure ofthe cloacal diaphragm to involute.
Esophageal atresia and tracheoesophageal fistula. A, Blind upper andlower esophageal segments. B, Blind upper segment with fistulabetween lower segment and trachea. C, Fistula between patentesophagus and trachea. Type B is the most common.
StenosisStenosis is an incomplete form of atresia in whichthe lumen is markedly reduced in caliber as aresult of fibrous thickening of the wall, resulting inpartial or complete obstruction.Stenosis may involve any part of the GI tract,although the esophagus and small intestine areaffected most often.Stenosis can also be caused by inflammatoryscarring, as may occur with chronicgastroesophageal reflux, irradiation, scleroderma,or caustic injury.
Congenital duplication cystsAre saccular or elongated cysticmasses that contain redundantsmooth muscle layers. Thesemay be present in theesophagus, small intestine, orcolon.
Diaphragmatic HerniaDiaphragmatic hernia occurs when incompleteformation of the diaphragm allows the abdominalviscera to herniate into the thoracic cavity.When severe, the space-filling effect of the displacedviscera can cause pulmonary hypoplasiathat is incompatible with life after birth.
Omphalocele• An omphalocele is a birth defect in which• the infants intestine or otherabdominal organs stick out of thebelly button (navel). In babies with anomphalocele, the intestines are covered only by athin layer of tissue and can be easily seen.• An omphalocele is a type of hernia. Hernia means"rupture.
Gastroschisis Gastroschisis represents acongenital defect characterized by a defectin the anterior abdominal wall throughwhich the abdominal contents freelyprotrude.Gastroschisis is similar to omphalocele except that itinvolves all of the layers ofthe abdominal wall, from theperitoneum to the skin.
Ectopia•Ectopic tissues (developmental rests)are common in the GI tract. The most frequent siteof ectopic gastric mucosa is the upperthird of the esophagus, where it is referred to asan inlet patch. While generally asymptomatic, acidreleased by gastric mucosa within the esophaguscan result in dysphagia, esophagitis, Barrettesophagus, or, rarely, adenocarcinoma.
•Ectopic pancreatic tissueoccurs less frequently and can be found in theesophagus or stomach. Like inlet patches, thesenodules are most often asymptomatic but canproduce damage and local inflammation.• When ectopic pancreatic tissue is present in thepylorus, inflammation and scarring may lead toobstruction. Because the restsmay bepresent within any layer of the gastric wall, theycan mimic invasive cancer.
Gastric heterotopia• Gastric heterotopia, small patches of ectopicgastric mucosa in the small bowel or colon,may present with occult blood loss due topeptic ulceration of adjacent mucosa.
Meckel Diverticulum• A true diverticulum is a blind outpouchingof the alimentary tract that is lined bymucosa, communicates with the lumen, andincludes all three layers of the bowel wall.• The most common type is the Meckeldiverticulum, which occurs in theileum.
• The Meckel diverticulum occurs as a result offailed involution of the vitellineduct, which connects the lumen of thedeveloping gut to the yolk sac. This solitarydiverticulum is a small pouch extending from theantimesenteric side of the bowel. It is a truediverticulum with a wall that includes mucosa,submucosa, and muscularis propria.
“rule of 2s”• Meckel diverticulae occur in approximately 2% ofthe population,• are generally present within 2 feet (85 cm) of theileocecal valve,• are approximately 2 inches (5 cm) long,• are twice as common in males as in females,• and are most often symptomatic by age 2(although only 4% of Meckel diverticulae are∼symptomatic).
• The mucosal lining of Meckel diverticulaemay resemble that of normal small intestine,but ectopic pancreatic or gastric tissue mayalso be present.• The latter may result in peptic ulceration ofadjacent small intestinal mucosa and presentwith occult bleeding or abdominal painresembling acute appendicitis or intestinalobstruction.
Meckel diverticulum. The blind pouch is locatedon the antimesenteric side of the small bowel
• Less commonly, congenital diverticulae occur inother parts of the small intestine and ascendingcolon.• Virtually all other diverticulae are acquired andeither lack muscularis entirely or have anattenuated muscularis propria.• Although acquired diverticulae may occur in theesophagus, stomach, and duodenum, the mostcommon site is the sigmoid colon.
Pyloric Stenosis• more common in males• Monozygotic twins have a high rate ofconcordance,• Family studies suggest a complex polygenicinheritance.• Turner syndrome and trisomy 18 are alsoassociated with the disease. Congenitalhypertrophic pyloric stenosis generally presents inthe second or third week of life as new-onsetregurgitation and persistent, projectile, nonbiliousvomiting.
• Physical examination reveals hyperperistalsis anda firm, ovoid abdominal mass. Edema andinflammatory changes in the mucosa andsubmucosa may aggravate the narrowing. Surgicalsplitting of the muscularis (myotomy) is curative.• Acquired pyloric stenosis occurs in adults as aconsequence of antral gastritis or peptic ulcersclose to the pylorus.• Carcinomas of the distal stomach and pancreasmay also narrow the pyloric channel due tofibrosis or malignant infiltration.
Hirschsprung DiseaseCongenital Megacolon• Hirschsprung disease occurs in approximately1 of 5000 live births. It may be isolated oroccur in combination with otherdevelopmental abnormalities; 10% of allcases occur in children with Down syndromeand serious neurologic abnormalities arepresent in another 5%.
Pathogenesis.• Hirschsprung disease, also known as congenitalaganglionic megacolon, results when the normalmigration of neural crest cells from cecum torectum is arrested prematurely or when theganglion cells undergo premature death. Thisproduces a distal intestinal segment that lacksboth the Meissner submucosal and the Auerbachmyenteric plexus (“aganglionosis”). Coordinatedperistaltic contractions are absent and functionalobstruction occurs, resulting in dilation proximalto the affected segment.
• The mechanisms underlying defective neural crestcell migration in Hirschsprung disease areunknown, but a genetic component is present innearly all cases and 4% of patients siblings areaffected. However, simple Mendelian inheritanceis not involved in most cases. Heterozygous loss-of-function mutations in the receptor tyrosinekinase RET account for the majority offamilial cases and approximately 15% of sporadiccases.
MorphologyDiagnosis of Hirschsprung disease requiresdocumenting the absence of ganglion cellswithin the affected segment. Because migration ofneural crest cells in the Meissner and Auerbachplexi are linked, it is possible to establish thediagnosis preoperatively by examining suctionbiopsy specimens. In addition to theircharacteristic morphology in hematoxylin andeosin (H&E)-stained sections, ganglion cells can beidentified using immunohistochemical stains foracetylcholinesterase.
• The rectum is always affected, but thelength of the additional involved segmentsvaries widely. Most cases are limited to therectum and sigmoid colon, but severe casescan involve the entire colon. The aganglionicregion may have a grossly normal orcontracted appearance, while the normallyinnervated proximal colon may undergoprogressive dilation.
• With time the proximal colon may becomemassively distended (megacolon), reachingdiameters of as much as 20 cm. Dilationmay stretch and thin the colonic wall to thepoint of rupture, which occurs mostfrequently near the cecum. Mucosalinflammation or shallow ulcers may also bepresent.
• These changes proximal to the diseasedsegment can make gross identification of theextent of aganglionosis difficult. Hence,intraoperative frozen-section analysis oftransmural sections is commonly used toconfirm the presence of ganglion cells at theanastamotic margin.
Hirschsprung disease. A, Preoperative barium enema study showingconstricted rectum (bottom of the image) and dilated sigmoid colon. B, Correspondingintraoperative photograph showing constricted rectum and dilation of the sigmoid colon.
Clinical Features• a failure to pass meconium in the immediatepostnatal period. Obstructive constipation follows,• The major threats to life are enterocolitis, fluidand electrolyte disturbances, perforation, andperitonitis.• The primary mode of treatment is surgicalresection of the aganglionic segment andanastamosis of the normal colon to the rectum.• .
Acquired megacolonAcquired megacolon may occur at any age as a resultof• Chagas disease,• obstruction by a neoplasm or inflammatorystricture,• Toxic megacolon complicating ulcerative colitis,visceral myopathy,• or in association with functional psychosomaticdisorders.Of these, only Chagas disease is associated with lossof ganglia