Meckel's diverticulum pathophysiology

The vitelline duct or the omphalomesenteric duct is the connection between the midgut and the yolk sac responsible for providing nutrition to the midgut, during fetal development. The vitelline duct subsequently undergoes involution, in the period between the fifth and the sixth weeks of gestation while the intestinal loop is rapidly pulled into the abdominal cavity. Failure of duct involution may lead to persistence of the proximal portion of omphalomesenteric duct, which may be referred to as the Meckel’s diverticulum. The Meckel’s diverticulum is a true diverticulum (comprising of all layers of intestinal wall i.e. mucosa, submucosa and muscularis propria). It arises from the antimesenteric border of the ileum and extends into the umbilical cord. The blood supply comes from the vitelline artery, which is a branch of the superior mesenteric artery, prone to torsion, ischemia, infarction, and obstruction. The diverticulum may contain ectopic tissue due to the presence of a pluripotent cell lining, faulty association between endodermal and neural crest cells and absence of inhibitory effect of the mesoderm on the local endoderm.

• During embryonic life, the vitelline duct or the omphalomesenteric duct is the connection between the midgut and the yolk sac responsible for providing nutrition to the midgut.^[2]
• In the period between the fifth and the sixth weeks of gestation, the vitelline duct involutes and disappears, while the bowel is rapidly pulled into the abdominal cavity.^[3]
• Failure of duct involution may lead to persistence of the omphalomesenteric duct with variable morphology:^[4][5][6]
  • Vitelline fistula draining through the umbilicus
  • Vitelline cysts
  • Fibrous bands connecting the umbilicus to the diverticulum that may twist to cause intestinal obstruction
  • Meckel’s diverticulum:^[4][7][8][9]
    • True diverticulum (comprising of all layers of intestinal wall i.e. mucosa, submucosa and muscularis propria)
    • Arises from the antimesenteric border of the ileum, extends into the umbilical cord
    • Supplied by the vitelline artery, branch of the Superior Mesenteric Artery (SMA), prone to torsion and subsequent ischemia, infarction and obstruction
    • May contain ectopic tissue due to the following reasons:
      • Presence of a pluripotent cell lining
      • Faulty association between endodermal and neural crest cells
      • Absence of inhibitory effect of the mesoderm on the local endoderm may also be responsible
    • Types of ectopic tissue:
      • Jejunal mucosa
      • Duodenal mucosa or Brunner’s tissue 
      • Gastric mucosa
      • Pancreatic tissue

• There is some evidence to suggest a familial association with the development of Meckel’s diverticulum, but this has not been adequately explored.^[10]

• Presence of other congenital anomalies:^[11][12]
  • Crohn’s disease
  • Omphalocele
  • Esophageal atresia
  • Anorectal malformations such as imperforate anus
  • Neurological and cardiovascular malformations

• On gross pathology, the features of Meckel’s diverticulum are as follows:
• Location:
  • Usually located 80cm proximal to the ileocecal junction
  • Along the antimesenteric border of the ileum
• Appearance:
  • Small pouch or a blind segment
• Length:
  • Variable, from less than 1cm to 8cm
• Size:
  • Lumen diameter: greater the ileum

• Microscopic pathology reveals normal small intestinal mucosa.
• Meckel’s diverticulum is a true diverticulum containing all three layers of the bowel wall:
  • Mucosa
  • Submucosa
  • Muscularis propria
• Heterotopic rests of other kinds of mucosa may be present:
  • Gastric
  • Colonic
  • Pancreatic

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