*3.1.1 Embryology*

Midgut development begins around the fifth week of gestation. The midgut starts as a vertical tube and has two connections: a ventral connection to the yolk sac via the omphalomesenteric (vitelline) duct and a dorsal attachment to the posterior abdominal wall, the mesentery [4–6]. The dorsal mesentery is the conduit for the superior mesenteric artery (SMA), which buds from the aorta, and delivers blood to the midgut. The lengthening gut tube outgrows the confines of the abdominal cavity and consequently herniates into the umbilical cord. As it elongates, it rotates

90° in a clockwise direction relative to the embryo (counterclockwise if visualized from the front). The midgut tube continues to grow extra-abdominally during gestational weeks 6–10. Around week 10, it retracts back into the abdominal cavity, rotating another 180° while doing so. Final intra-abdominal growth and fixation ensue, placing the cecum in the right lower quadrant and the duodeno-jejunal junction to the left of the upper midline, inferior to the SMA. The mesentery broadens, fanning out from its root in the posterior abdominal wall, to support the blood vessels and lymphatics that serve the jejunum, ileum, cecum/appendix, ascending colon and proximal 2/3 of the transverse colon. It is believed that ischemic events during this period cause jejunoileal atresia.

#### *3.1.2 Clinical presentation*

Atresia causes a structural obstruction that prevents passage of meconium in the first 24–48 h of life and results in bilious emesis. On physical exam, the abdomen will be distended.

Jejunoileal atresia is classified into four types (**Figures 4A–E**). Type 1 is an intraluminal web with intact mesentery (**Figure 4A**). The seromuscular layers of bowel remain in continuity. Type 2 also has an intact mesentery, but the two ends of bowel are disconnected by a fibrous cord (**Figure 4B**). Type 3a has a small v-shaped mesenteric defect that separates two blind ends of bowel (**Figure 4C**). In type 3b disease, known as an "apple-peel" or "Christmas-tree" deformity, a large mesenteric defect separates the proximal and distal ends of bowel. The proximal pouch is very dilated, and the distal collapsed bowel is supplied by a small vessel around which it repeatedly winds (**Figure 4D**). Type 4 consists of numerous blind ended segments of bowel with discontinuous mesentery, appearing as a "string of sausages" (**Figure 4E**).

#### *3.1.3 Diagnosis*

Abdominal x-ray will reveal dilated portions of bowel proximal to the site of obstruction with collapsed loops and paucity of air in the distal bowel. Contrast enema will demonstrate an abrupt transition from the filling to non-filling segments of small bowel and the colon will be appear small, <1 cm diameter, due to lack of use. In all cases of bilious emesis, an UGI series is warranted to rule out malrotation, a surgical emergency. UGI will reveal contrast filling in the stomach and proximal bowel, with abrupt cessation of contrast filling at the point of atresia.

#### *3.1.4 Surgical management*

Initial management begins with insertion of an oro- or nasogastric tube for bowel decompression and fluid resuscitation. Resection of atretic segments with end-to-end anastomoses is the procedure of choice; however, this can prove quite difficult in cases where ends of bowel are greatly mismatched in diameter. In such circumstances, the anastomosis is created in a fashion similar to duodenoduodenostomy in which the smaller end of bowel is incised longitudinally along its anti-mesenteric border to fit the end of the larger caliber bowel. Prior to completing the anastomosis, the entire length of the bowel must be inspected to ensure there are no intraluminal webs or fenestrations that may cause persistent obstruction. The goal is to resect all defunct bowel segments while maintaining enough length to ensure adequate resorptive capacity. If the ileocecal valve is spared, enteral nutrition can be tolerated with as little as 15–20 cm of small bowel. Otherwise, a length

**95**

*3.1.5 Outcomes*

**Figure 4.**

of approximately 40 cm is required [4]. Mesenteric defects are closed, taking care

*(A) Type 1 jejunoileal atresia. (B) Type 2 jejunoileal atresia. (C) Type 3a jejunoileal atresia. (D) Type 3b* 

Intestinal dysmotility, even in infants that have adequate remaining bowel length, may occur for many weeks following repair. Infants with short bowel

not to disrupt the feeding blood vessels.

*jejunoileal atresia. (E) Type 4 jejunoileal atresia.*

*Congenital Anomalies of the Gastrointestinal Tract DOI: http://dx.doi.org/10.5772/intechopen.92588*

#### **Figure 4.**

*Congenital Anomalies in Newborn Infants - Clinical and Etiopathological Perspectives*

during this period cause jejunoileal atresia.

*3.1.2 Clinical presentation*

will be distended.

(**Figure 4E**).

*3.1.3 Diagnosis*

*3.1.4 Surgical management*

90° in a clockwise direction relative to the embryo (counterclockwise if visualized from the front). The midgut tube continues to grow extra-abdominally during gestational weeks 6–10. Around week 10, it retracts back into the abdominal cavity, rotating another 180° while doing so. Final intra-abdominal growth and fixation ensue, placing the cecum in the right lower quadrant and the duodeno-jejunal junction to the left of the upper midline, inferior to the SMA. The mesentery broadens, fanning out from its root in the posterior abdominal wall, to support the blood vessels and lymphatics that serve the jejunum, ileum, cecum/appendix, ascending colon and proximal 2/3 of the transverse colon. It is believed that ischemic events

Atresia causes a structural obstruction that prevents passage of meconium in the first 24–48 h of life and results in bilious emesis. On physical exam, the abdomen

Jejunoileal atresia is classified into four types (**Figures 4A–E**). Type 1 is an intraluminal web with intact mesentery (**Figure 4A**). The seromuscular layers of bowel remain in continuity. Type 2 also has an intact mesentery, but the two ends of bowel are disconnected by a fibrous cord (**Figure 4B**). Type 3a has a small v-shaped mesenteric defect that separates two blind ends of bowel (**Figure 4C**). In type 3b disease, known as an "apple-peel" or "Christmas-tree" deformity, a large mesenteric defect separates the proximal and distal ends of bowel. The proximal pouch is very dilated, and the distal collapsed bowel is supplied by a small vessel around which it repeatedly winds (**Figure 4D**). Type 4 consists of numerous blind ended segments of bowel with discontinuous mesentery, appearing as a "string of sausages"

Abdominal x-ray will reveal dilated portions of bowel proximal to the site of obstruction with collapsed loops and paucity of air in the distal bowel. Contrast enema will demonstrate an abrupt transition from the filling to non-filling segments of small bowel and the colon will be appear small, <1 cm diameter, due to lack of use. In all cases of bilious emesis, an UGI series is warranted to rule out malrotation, a surgical emergency. UGI will reveal contrast filling in the stomach and proximal bowel, with abrupt cessation of contrast filling at the point of atresia.

Initial management begins with insertion of an oro- or nasogastric tube for bowel decompression and fluid resuscitation. Resection of atretic segments with end-to-end anastomoses is the procedure of choice; however, this can prove quite difficult in cases where ends of bowel are greatly mismatched in diameter. In such circumstances, the anastomosis is created in a fashion similar to duodenoduodenostomy in which the smaller end of bowel is incised longitudinally along its anti-mesenteric border to fit the end of the larger caliber bowel. Prior to completing the anastomosis, the entire length of the bowel must be inspected to ensure there are no intraluminal webs or fenestrations that may cause persistent obstruction. The goal is to resect all defunct bowel segments while maintaining enough length to ensure adequate resorptive capacity. If the ileocecal valve is spared, enteral nutrition can be tolerated with as little as 15–20 cm of small bowel. Otherwise, a length

**94**

*(A) Type 1 jejunoileal atresia. (B) Type 2 jejunoileal atresia. (C) Type 3a jejunoileal atresia. (D) Type 3b jejunoileal atresia. (E) Type 4 jejunoileal atresia.*

of approximately 40 cm is required [4]. Mesenteric defects are closed, taking care not to disrupt the feeding blood vessels.

#### *3.1.5 Outcomes*

Intestinal dysmotility, even in infants that have adequate remaining bowel length, may occur for many weeks following repair. Infants with short bowel

syndrome, those with less than 40 cm, often require long term parenteral nutrition, which itself carries risks of sepsis and liver damage. Nonetheless, overall mortality is low and related to co-morbidities, such as low birth weight and/or cardiac defects.
