This occurs when the diverticulum inverts into the lumen of the ileum, due to either:An active peristaltic mechanism of the diverticulum that attempts to remove irritating factors
A passive process such as the transit of food

Umbilical anomalies
Anomalies between the diverticulum and umbilicus may include the presence of fibrous cord, cyst, fistula, or sinus, leading to:
Infection or excoriation of periumbilical skin, resulting in a discharging sinus
Recurrent infection and healing of sinus
Abscess formation in the abdominal wall
Fibrous cord increases the risk of volvulus formation and internal herniation

Neoplasm
Tumors in Meckels diverticulum may cause bleeding, acute abdominal pain, gastrointestinal obstruction, perforation or intussusception. Benign tumors:Leiomyoma
Lipoma
Vascular and neuromuscular hamartomaMalignant tumors:Carcinoids: most common, 44%
Mesenchymal tumors: Leiomyosarcoma, peripheral nerve sheath and gastrointestinal stromal tumors, 35%
Adenocarcinoma, 16%
Desmoplastic small round cell tumor

Other complications
A diverticulum inside a Meckels diverticulum (daughter diverticula)
Stones and phytobezoar (a bezoar of vegetable fibers) in Meckels diverticulum
Vesicodiverticular fistula

Pathophysiology
The omphalomesenteric duct (omphaloenteric duct, vitelline duct, or yolk stalk) normally connects the embryonic midgut to the yolk sac ventrally, providing nutrients to the midgut during embryonic development. The vitelline duct narrows progressively and disappears between the 5th and 8th weeks of gestation.In Meckels diverticulum, the proximal part of vitelline duct fails to regress and involute, which remains as a remnant of variable length and location. The solitary diverticulum lies on the antimesenteric border of the ileum (opposite to the mesenteric attachment) and extends into the umbilical cord of the embryo. The left and right vitelline arteries originate from the primitive dorsal aorta, and travel with the vitelline duct.
The right becomes the superior mesenteric artery that supplies a terminal branch to the diverticulum, while the left involutes. Having its own blood supply, Meckels diverticulum is susceptible to obstruction or infection. Meckels diverticulum is located in the distal ileum, usually within 60–100 cm (2 feet) of the ileocecal valve. This blind segment or small pouch is about 3–6 cm (2 inch) long and may have a greater lumen diameter than that of the ileum. It runs antimesenterically and has its own blood supply. It is a remnant of the connection from the yolk sac to the small intestine present during embryonic development. It is a true diverticulum, consisting of all 3 layers of the bowel wall which are mucosa, submucosa and muscularis propria.As the vitelline duct is made up of pluripotent cell lining, Meckels diverticulum may harbor abnormal tissues, containing embryonic remnants of other tissue types. Jejunal, duodenal mucosa or Brunners tissue were each found in 2% of ectopic cases. Heterotopic rests of gastric mucosa and pancreatic tissue are seen in 60% and 6% of cases respectively. Heterotopic means the displacement of an organ from its normal anatomic location. Inflammation of this Meckels diverticulum may mimic appendicitis.