Embryology

Question 1

Normal GI embryology:

Foregut

Midgut

Hindgut

Answer 1

Foregut - pharynx to duodenum

Midgut - duodenum to proximal 2/3 transverse colon

Hindgut - distal 1/3 transverse colon –> anal canal above pectinate line

Midgut Development:

6th week - midgut herniates through umbilical ring

10th week - returns to abdominal cavity + rotates around SMA (total 270 degrees counterclockwise)

Question 2

Ventral Wall Defects

Developmental defects due to failure of:

Rostral fold closure -

Lateral fold closure -

Caudal fold closure -

Answer 2

Rostral fold closure –> sternal defects

Lateral fold closure –> omphalocele, gastroschisis

Caudal fold closure –> bladder exstrophy

Question 3

Tracheoesophageal anomalies

Most common type:

Clinical findings:

Clinical test:

Answer 3

• Pure EA (atresia or stenosis)
• Pure TEF (H-type)
• Esophageal atresia (EA) + distal TEF (85%)

Clinical Findings:

• Polyhydramnios in utero
• Neonates drool, choke, vomit with first feeding
• TEF allows air to enter stomach (visible on CXR)
• Cyanosis (2ndary to laryngospasm - to avoid reflux-related aspiration)
• In pure EA, CXR shows gasless abdomen

Clinical Test:

Failure to pass nasogastric tube into stomach

Question 4

Intestinal Atresia

Clinical Presentation:

Three types:

Answer 4

Presents with bilious vomiting, abdominal distension within first 1-2 days of life

1. Duodenal atresia - failure to recanalize at 8-10 weeks –> dilation of stomach + proximal duodenum (“double bubble” on CXR) **Association with DS
2. Jejunal and ileal atresia - vascular injury: disruption of mesenteric vessels –> ischemic necrosis –> segmental resorption (bowel discontinuity or “apple peel”) Bilious vomiting **Association with gastroschisis
3. Colonic atresia - path: unknown **Association: Hirschsprung Disease

Question 5

Hypertrophic pyloric stenosis

Description:

Clinical Findings:

Association:

Treatment:

Answer 5

• Most common cause of gastric outlet obstruction in infants (1:600)
• More common in firstborn males

Clinical Findings:

• Palpable “olive” mass in epigastric region
• Nonbilious projectile vomiting at ~2-6 weeks old (don’t see symptoms right away)
• Hypokalemic hypochloremic metabolic alkalosis (2ndary to vomiting of gastric acid + subsequent volume contraction)

Associated with:

• Exposure to macrolides

Treatment:

• surgical incision (pyloromyotomy)

Question 6

Pancreas and Spleen Embryology

Where is the pancreas derived from?

Where is the spleen derived from?

Answer 6

Pancreas –> derived from foregut

• Ventral pancreatic buds contribute to uncinate process and main pancreatic duct
• Dorsal pancreatic bud alone becomes body, tail, isthmus, accessory pancreatic duct
• Both ventral and dorsal buds contribute to pancreatic head

Spleen –> arises in mesentery of stomach (mesodermal) but has foregut supply (celiac trunk –> splenic artery)

Question 7

Annular pancreas

Pancreas divisum

Answer 7

Annular pancreas

• Ventral pancreatic bud abnormally encircles 2nd part of duodenum
• Forms ring of pancreatic tissue –> duodenal narrowing + nonbilious vomiting

Pancreas divisum

• Ventral and dorsal parts failure to fuse at 8 wks
• Common anomaly; mostly asymptomatic but may cause chronic abdominal pain and/or pancreatitis

Question 8

Gastroschisis

Answer 8

Lateral fold closure

Extrusion of abdominal contents through abdominal folds (typically right of umbilicus); not covered by peritoneum

Question 9

Omphalocele

Answer 9

Lateral fold closure

Persistence of herniation of abdominal contents into umbilical cord; SEALED by peritoneum