GI embryology

Imperforate anus

Abnormal development of anal-rectal structures Absence of anal opening is most common in - Urorectal fistula - Urovesical fistula - Urovaginal fistula Partnered malformation - Renal agenesis - Hypospadias (urethra opens at base of penis) - Epispadias - Bladder extrophy Meconium discharge from urethra or vagina

Annular pancreas

Abnormal rotation of *ventral pancreatic bud* forms a ring of pancreatic tissue - Encircles 2nd part of duodenum May cause - Duodenal narrowing - Vomiting Most are asymptomatic

Hirschsprung disease diagnosis

Absence of ganglionic cells on rectal suction biopsy Biopsied at *submucosa of rectum (narrow segment)* - Due to migration caudally

Tracheoesophageal fistula

Allow air to enter stomach (visible on CXR). Cyanosis is 2° to laryngospasm (to avoid re flux-related aspiration). Clinical test: failure to pass nasogastric tube into stomach.

Malrotation

Anomaly of midgut rotation during fetal development→ improper positioning of bowel - Small bowel clumped on the right side Formation of fibrous bands (Ladd bands) Can lead to - Volvulus→ Gangrene - Duodenal obstruction

Spleen embryology

Arises in mesentery of stomach (hence is mesodermal) but has *foregut supply* (*celiac trunk splenic artery*) Venous return - Splenic vein to portal circulation rather than symtemic

Omphalocele associations

Congenital anomalies - Trisomies 13 and 18 - Beckwith-Wiedemann syndrome Structural abnormalities -Cardiac, GU, neural tube

Colonic atresia

Congenital failure of development of the distal rectum and anus Findings - Constipation - Ab distention Associations - Hirschsprung disease

Hirschsprung disease

Congenital megacolon Lack of ganglion cells/ enteric nervous plexuses (Auerbach and Meissner plexuses) in distal segment of colon ALWAYS affect *rectum* Failure of neural crest migration Associated w RET mutations Increase risk with Down syndrome *RET* mutation in the *RE*c*T*um

Meckel's diverticulum presentation

During first 2 years of life Hematochezia -Passage of fresh blood through the anus Melena (less commonly) - Black tarry stool - UGI bleeding RLQ pain Intussusception - Current jelly stools - Colicky ab pain Volvulus Obstruction near terminal ileum

Trachealesophageal anomalies

Esophageal atresia (EA) with distal tracheoesophageal fistula (TEF) -Most common (85%) - Presents as polyhydramnios in utero (due to inability of fetus to swallow amniotic fluid). -Neonates drool, choke, and vomit with first feeding

Gastroschisis

Extrusion of abdominal contents through abdominal folds (typically right of umbilicus) Not covered by peritoneum or amnion;

Omphalocele

Failure of lateral walls to migrate at umbilical ring - Persistent midline herniation of abdominal contents into umbilical cord Surrounded by peritoneum

Duodenal atresia

Failure to recanalize *Bilious* or *non bilious emesis* Associated with - Double bubble (dilated stomach, proximal duodenum on X-ray) - Down syndrome

Primitive gut tube

Foregut Midgut Hindgut

Ectopy

Functionally normal cells in wrong location

Foregut

GIves rise to - Esophagus - Stomach - Liver - Gallbladder - Pancreas - Upper duodenum Supplied by: Celiac trunk

Neural crest cells

Give rise to ganglion cells of - Submucosal (Meissner) plexi - Myenteric (Auerbach) plexi Responsible for peristalsis Move *caudally*

Midgut

Lower duodenum Small intestines Ascending colon 2/3 transverse colon Supplied: SMA

Intussusception causes

Majority in children Most common - Meckel diverticulum (children) - Lymphoid hyperplasia (children, from infection- Terminal ileum to cecum) - Intraluminal mass/ tumor (adults) May be associated with - Rotavirus vaccine - Henoch-Schönlein purpura - Recent viral infection (eg, adenovirus; Peyer patch hypertrophy creates lead point)

Vitelline sinus

Partial closure of vitelline duct Patent portion open at umbilicus

Meckel's diverticulum

Persistence of the *vitelline (omphalomesenteric) duct* May contain - *Ectopic* acid secreting gastric mucosa - *Pancreatic tissue* - Can cause GI bleeding The rule of 2's: *2* x as likely in males *2* inches long *2* feet from the ileocecal valve *2%* of population Commonly presents in the first 2 years of life

Intestinal atresia Presentation

Presentation - Bilious vomiting and abdominal distention within first 1-2 days of life Types - Duodenal atresia - Jejunal and ileal atresia

Hypertrophic pyloric stenosis findings

Symptoms don't occur until *2 weeks after* Palpable olive- shaped mass in epigastric region Visible peristaltic waves *Nonbilious* projectile vomiting (~2-6 weeks old) - Food hasn't met duodenum yet Results in: - Hypokalemic hypochloremic metabolic acidosis (2° to vomiting of gastric acid and subsequent volume contraction)

Intussusception

Telecoping of proximal bowel segment into a distal segment - Commonly at *ileocecal junction*→ intermittent ab pain - Currant jelly stools Draw legs to ease pain Ultrasound - Target sign

Hypertrophic pyloric stenosis ultrasound

Thickened and lengthen pylorus

Hindgut

Transverse colon Descending colon Sigmoid colon Rectum Supplied: IMA

Volvulus

Twisting of portion of bowel around it's mesentery - Can lead to obstruction and infarction Can occur throughout the GI tract Midgut volvulus - More common in infants Sigmoid volvulus - Coffee bean sign on X-ray - More common in elderly

Jejunal and ileal atresia

Vascular Injury Disruption of mesenteric vessels→ischemic necrosis→segmental resorption (bowel discontinuity or "apple peel") Associated - Gastroschisis (baby's intestines are found outside of the baby's body)

Pancreas divisum

Ventral and dorsal parts fail to fuse at 8 weeks - Pancreatic secretions drained via 2 separate duct system Dominant dorsal duct (of Santornini) opens into duodenum via minor papilla - Responsible for majority of pancreas Common anomaly; mostly asymptomatic - May cause chronic ab pain and/ or pancreatitis

Jejunal and ileal atresia presentation

*Bilious* emesis Ab distention

Hypertrophic pyloric stenosis

*Hypertrophy* of pyloric muscularis mucosae Most common cause of gastric outlet obstruction in infants (1:600) Commonly seen in: firstborn males Associated with exposure to *macrolides* Treatment is surgical incision (pyloromyotomy).

Midgut rotation

6th week - Rapid growth of intestines and liver despite slower growth of ab cavity 10th week - Complete 270 degree turn counterclockwise around SMA

Meckel's diverticulum Diagnosis

99mmTc-pertechnetate scan Identifies gastric mucosa

Hirschsprung disease presentation

Bilious emesis Ab distention Failure to pass meconium within 48 hours Chronic constipation Explosive expulsion of feces (squirt sign) - Cause empty rectum on digital exam

Intestinal malrotation

Cecum in RUQ fixed with fibrous bands (Ladd's band) to second part of duodenum - Entire midgut is fixed to SMA→ Intestinal obstruction from duodenal compression Symptoms - Bilious vomiting during 1st days of life - Impaired perfusion - Volvulus

Intussusception symptoms

Currant jelly stools - Contain blood and mucus Colickly intermittent ab pain Nausea Vomiting Palpable in LRQ

True Diverticulum

Outpouching lined by all layers - Mucosa - Submucosa - Muscularis (propria and adventitia) Contains *Ectopic Gastric Secretion* - Cause ulceration of adjacent mucosa - Lower GI bleeding Eg. Meckel diverticulum

False Diverticulum

Outpouching of - Mucosa - Submucosa Eg. Colonic and Zenker

Pancreas embryology

Derived from foregut Ventral pancreatic buds (primordium) - Uncinate process - Main pancreatic duct - Inferior/ posterior portion of head Dorsal pancreatic bud - Body - Tail - Isthmus - Accessory pancreatic duct Ventral and dorsal buds - Pancreatic head

Persistent vitelline duct (fistula)

Occurs due to complete failure of vitelline duct to close Small connection between the intestinal lumen and the outside of body Meconium discharge through umbilicus soon after birth