GIT

• Congenital abnormalities of the gastrointestinal tract

  • Atresia, Fistulae, and Duplications
  • Diaphragmatic Hernia
  • Omphalocoele and Gastroschisis
  • Ectopia
  • Meckel's Diverticulum
  • Congenital Hypertrophic Pyloric Stenosis
  • Hirschsprung Disease (Congenital Aganglionic Megacolon)

  
• Atresia


  Incomplete formation, a thin non-canalized cord replaces a segment causing mechanical obstruction
• Fistula


  A connection between the upper or lower pouch of the esophagus to a bronchus or the trachea

  
• Diaphragmatic Hernia


  Incomplete formation of the diaphragm allows the abdominal viscera to herniate into the thoracic cavity
• Omphalocoele


  Herniates into the ventral membranous sac, can be surgically repaired
• Gastroschisis


  Involves all the layers of the abdominal wall, from the peritoneum to the skin

  
• Ectopic gastric mucosa


  Most frequent site is the upper third of the esophagus, referred to as an inlet patch
• Ectopic Pancreatic Tissue


  Occurs less frequently, located in the esophagus or stomach
• Gastric Heterotropia


  Small patches of ectopic gastric muscosa in the small bowel or colon, may present with occult blood due to peptic ulceration of adjacent mucosa

  
• Meckel's Diverticulum


  A true diverticulum (a blind outpouching of the GIT that communicates with the lumen and includes 3 layer of bowel wall), occurs in the Ileum as a result of failed involution of the vitelline duct
• Characteristics of Meckel's Diverticulum (Rule of 2s)

  • Occurs in 2% of the population
  • Generally present within 2 feet (60cm) of the ileocecal valve
  • Approximately 2 inches long
  • Twice common in males
  • Most often symptomatic at the age of 2

  
• Congenital Hypertrophic Pyloric Stenosis

  Hyperplasia of pyloric muscularis propria, which obstructs the gastric outflow tract, edema and inflammation may aggravate the narrowing
• Hirschsprung Disease (Congenital Aganglionic Megacolon)


  Results when normal migration of neural crest cells from cecum to rectum is arrested prematurely or when ganglion cells undergo premature death, producing a distal intestinal segment that lacks both Messner's and Myenteric (Auerbach) Plexus, leading to functional obstruction and dilation of the proximal segment
• Rectum is always affected in Hirschsprung Disease
• Acquired Megacolon


  Occur at any age as a result of Chagas Disease, neoplastic obstruction, inflammatory stricture, complication of ulcerative colitis, visceral myopathy or functional psychosomatic disorders
• Esophageal Obstructions


  Can be due to mechanical or functional (peristaltic) obstruction
• Forms of esophageal dysmotility

  • Nutcracker Esophagus - high amplitude contractions of distal esophagus
  • Diffuse Esophageal Spasm - repetitive, simultaneous contractions of the distal esophageal muscles
  • Hypertensive Lower Esophageal Sphincter - absence of altered patterns, can be distinguished from achalasia the latter includes reduced esophageal peristalsis
• Pharyngoesophageal Diverticulum


  • Epiphrenic Diverticulum - due to increased wall stress, esophageal dysmotility can result in the development of small diverticulae located above the lower esophageal sphincter
  • Zenker's Diverticulum - impaired relaxation of the cricopharyngeus muscle after swallowing can result to increased pressure in distal pharynx, located immediately above the upper esophageal sphincter
  • Traction Diverticulum - located near the middle portion of the esophagus
• Benign Esophageal Stenosis


  Narrowing of the lumen caused by fibrous thickening of the submucosa and atrophy of muscularis propria, most often due to inflammation and scarring in chronic GERD

  
• Esophageal Mucosal Webs


  Idiopathic, ledge-like protrusions of mucosa that may cause obstruction, encountered most frequently in women over age 40, associated with GERD, Chronic GVHD, or blistering skin disease
• Esophageal / Schatzki Rings


  Similar to webs but are circumferential, thicker, and include mucosa, submucosa, and hypetrophic muscular propria
• Achalasia


  Characterized by a triad: incomplete LES relaxation, increased LES tone, and aperistalsis of esophagus, results from impaired smooth muscle relaxation leading to esophageal obstruction
• Primary Achalasia


  Idiopathic, failure of distal esophageal inhibitory neurons (ganglion cell degeneration)
• Secondary Achalasia


  May arise from Chagas disease caused by Trypanosoma cruzi leading to destruction or myenteric plexus
• Mallory-Weiss Syndrome


  Longitudinal mucosal tears near gastroesophageal junction, most often associated with severe retching or vomiting secondary to acute alcohol intoxication
• Boerhave Syndrome


  Characterized by transmural tearing and rupture of the distal esophagus, produces severe mediastinitis

  
• Chemical and Infectious Esophagitis


  May be damaged by variety of irritants like alcohol, erosive acids or alkalis, excessive hot fluids, and heavy smoking, or caused by herpes simplex virus, CMV, or fungi in debilitated or immunosuppressed patients
• Herpesvirus causes punched out ulcers with nuclear viral inclusions within the rim of degenerating epithelial cells at the ulcer margin

  
• CMV causes shallower ulcerations and characteristic nuclear and cytoplasmic inclusions within capillary endothelium and stromal cells
• Candida causes adherent, gray-white pseudomembranes composed of densely matted fungal hyphae and inflammatory cells
• Chemicals cause outright necrosis of the esophageal wall, pills lodge and dissolve in the esophagus causing injury
• Iatrogenic esophageal injury


  Caused by cytotoxic chemotherapy, radiation therapy, or GVHD

  
• Esophageal infection


  Uncommon in healthy individuals, can be caused by herpes simplex virus, CMV, or fungi in debilitated or immunosuppressed patients
• Herpes simplex virus esophagitis

  • Punched out ulcers, biopsy demonstrates nuclear viral inclusions within the rim of degenerating epithelial cells at the ulcer margin

  
• CMV esophagitis


  • Causes shallower ulcerations and characteristic nuclear and cytoplasmic inclusions within capillary endothelium and stromal cells, IHC stains are also sensitive

  
• Candida esophagitis


  • Adherent, gray-white pseudomembranes composed of densely matted fungal hyphae and inflammatory cells
• Morphology of esophagitis


  • Chemical - outright necrosis of the esophageal wall
  • Pill-induced - ulceration with superficial necrosis, granulation tissue and fibrosis
  • Irradiation - intimal proliferation and luminal narrowing of submucosal and mural blood vessels
  • Infection - non-pathogenic oral bacteria may invade lamina propria and cause necrosis of overlying mucosa

  
• Stratified squamous epithelium of esophagus

  • Resistant to abrasion but sensitive to acids, submucosal glands contribute to mucosal protection by secreting mucin and bicarbonate
• Lower esophageal sphincter (LES)

  Prevents reflux of acidic gastric contents, most frequent cause of esophagitis and most common outpatient GI diagnosis, associated clinical condition is gastroesophageal reflux disease (GERD)
• Pathogenesis of GERD


  1. Most common cause is transient LES relaxation, mediated via vagal pathways and can be triggered by gastric distention

  2. Other conditions that decrease LES tone or increase abdominal pressure that contribute to GERD include alcohol, tobacco use, obesity, CNS depressants, pregnancy, and hiatal hernia