Meckel's diverticulum

Meckel's diverticulum - Pathogenesis

Pathogenesis → Meckel's diverticulum results from the incomplete obliteration of the vitelline duct (=omphalomesenteric duct = Dottergang) → The incomplete obliteration leads to the formation of a true diverticulum of the small intestines

Meckel's diverticulum - Vascular supply Which vessel provides the rich blood supply to the diverticulum?

Vascular supply → The vitelline artery which is a branch of the superior mesenteric artery supplies the Meckel's diverticulum

Meckel's scan - Definition - Agents influencing a Meckel's scan

Definition → A Meckel's scan is a nuclear medicine study with 99m technetium pertechnetate → 99m technetium pertechnetate is administered intravenously and a scintigraphy is performed subsequently → 99m technetium pertechnetate has an affinity for gastric mucosa so in theory a Meckel's diverticulum containing gastric mucosa (less than 25% of cases) should show up on the scintigraphy → Meckel's diverticula lacking gastric mucosa will not show up on a Meckel's scan Agents influencing a Meckel's scan Aluminium hydroxide → Aluminium hydroxide limits the mucosal localization of radiotracer Cimetidine → Cimetidine promotes retention of theradiotracer

Gastric heterotopia - Definition

Definition → Heterotopia refers to presence of a particular tissue type at a non-physiological site, but usually co-existing with original tissue in its correct anatomical location → In other words it implies ectopic tissue in addition to retention of the original tissue type → Gastric heterotopia therefore describes the presence of ectopic gastric tissue in combination with normal small bowel mucosa

Obscure lower gastrointestinal bleeding - Definition

Definition → Obscure gastrointestinal bleeding (OGIB) is defined as recurrent or persistent gastrointestinal bleeding from a source that cannot be identified using upper or lower endoscopy

Meckel's diverticulum - Definition diverticulum - Classification of diverticula - Definition Meckel's diverticulum

Definition diverticulum → A diverticulum is an outpouching of a hollow (or fluid filled) structure in the body Classification of diverticula → Diverticula can be classified as true or false diverticula → True diverticula involve all layers including muscularis propria and adventitia → False diverticula involve only the submucosa and mucosa (ie diverticulosis) Definition Meckel's diverticulum → A Meckel's diverticulum is a true diverticulum of the small intestines containing all layers of the small bowel wall → The Meckel diverticulum is a persistent remnant of the omphalomesenteric duct (Dottergang) and is the most common congenital anomaly of the GI tract

Meckel's diverticulum - Diagnostic workup

Definitive diagnosis → Meckel's scan → Mesenteric arteriography (Angiography) → Abdominal exploration → Meckel's scan is more likely to be diagnostic in a patient who presents with gastrointestinal bleeding compared to one who present with other nonspecific symptoms

Meckel's diverticulum - Management of asymptomatic, incidental diverticula - Risk of malignancy

Management of asymptomatic, incidental diverticula → Historically, the view on optimal treatment for incidentally found Meckel's diverticulum has been alternating, resulting in authors advocating for and against preventive resection → In the most recent literature, focus on optimal treatment strategy for incidental Meckel's diverticulum is pointed more towards individual, case-specific treatment by determination of risk factors Risk factors → Patient age < 50 years → Male sex → Diverticulum length > 2 cm → Ectopic or abnormal features within a diverticulum that all are associated with symptomatic diverticulum and, hence, would favor resection upon detection Risk of malignancy → The overall risk of tumor in Meckel's diverticulum is low → A retrospective review of 629 patients operated for Meckel's diverticulum at the Mayo Clinic found on histology of the resected specimens that 5.1% of the 629 patients (N=19) had evidence of malignancy with NET being the most prevalent type (63%), followed by GIST (10%), adenocarcinoma (5%) and pancreatic epithelial neoplasia (5%) → The authors conclude that although malignancy in Meckel's diverticulum is a rare phenomenon, the consequences of an untreated cancer with high risk of metastases justify prophylactic resection of incidental Meckel's diverticulum (Lindeman et al, Current Gastroenterology Reports, 2020)

Meckel's diverticulum - Most common type of ectopic tissue

Most common type of ectopic tissue → The most common ectopic tissue in a Meckel's diverticulum is gastric in origin (gastric heterotopia) → Pancreatic and duodenal mucosa have also been identified (pancreatic heterotopia, duodenal heterotopica)

Meckel's diverticulum - Pathogenesis of GI bleeding

Pathogenesis of GI bleeding → Meckel's diverticula that contain ectopic gastric mucosa are generally associated with bleeding → The ectopic gastic mucosa secrets acid thereby leading to ulceration of the sourrounding small bowel mucosa → The site of ulceration is adjacent to or just downstream from the diverticulum not from the mucosa or ectopic tissue within the diverticulum

Meckel's diverticulum - Pathogenesis of intestinal obstruction

Pathogenesis of intestinal obstruction Intussusception → Intussusception refers to the invagination (telescoping) of a part of the intestine into itself → Intussusception needs a lead point to develop → Meckel's diverticulum can act as the lead point Volvulus → The intestines (usually the small bowel) twists around a fibrous band often associated with Meckel's diverticulum (from the diverticulum to the umbilicus) or other adhesions Abdominal wall hernia → Meckel's diverticulum can incarcerated in an abdominal wall hernia (inguinal, femoral or umbilical) Meckel's diverticulitis → The inflammation of the diverticulum or the adjacent small bowel can result in reduced intraluminal diameter which leads to partial or complete bowel obstruction

Meckel's diverticulum - Rules of 2 What classic features of Meckel's Diverticulum are described by the *rule of 2s*?

Rules of 2 2% of the population → Meckel's Diverticulum occurs in about 2% of the population *2% symptomatic* → 2% of the ones who have it become symptomatic over the course of their lives Ratio is 2:1 → Male to female 2:1 2 feet → The diverticulum is located within 2 feet (60cm) of the ileocecal valve 2 inch → The diverticulum can be 2 inches in length → In clinical practice the size of a Meckel's diverticulum can vary

Meckel's diverticulum - Clinical presentation - When to suspect Meckel's diverticulum 1) What may be presenting symptoms of Meckel's diverticulum? 2) How does clinical presentation differ with regard to age group (children/adults)? 3) When should you suspect Meckel's diverticulum?

Symptoms → Gastrointestinal bleeding → Intestinal obstruction → Acute abdominal pain → Bleeding can be chronic and insidious or acute and massive → The clinical features (symptoms, laboratory, physical exam, imaging) of a patient with a Meckel's diverticulum are nonspecific Age variation → Children present more often than adults with GI bleeding → Adults present more often with symptoms of small bowel obstruction When to suspect Meckel's diverticulum → In children with painless lower gastrointestinal bleeding → In children with intussusecption, particularly recurrent intussusception → In patients with features of acute appendicitis, particularly when the appendix has already been removed → In adults with obscure gastrointestinal bleeding

Embryology - Define vitelline duct - Anatomical patterns arising form an incomplete obliteration of the omphalomesenteric duct

Vitelline duct → The vitelline duct (omphalomesenteric duct) is a small tube that connects the yolk sac (Dottersack) to the midgut lumen in the developing embryo → The vitelline duct normally obliterates between the 5th and 6th week of human gestation Consequences of an incompletely obliterated duct Omphalomesenteric cysts Omphalomesenteric fistualae → Omphalomesenteric fistulae drain through the umbilicus Fibrous bands → Fibrous bands from the diverticulum to the umbilicus → The circumstance that the small bowel is attached to the umbilicus via a fibrous band predisposes to small bowel obstruction Diverticulum without additional attachment → Commonly referred to as Meckel's diverticulum

Meckel's diverticulum - When to suspect a Meckel's diverticulum as a source of lower GI bleeding

When to suspect a Meckel's diverticulum as a source of lower GI bleeding Children → In children less than 10 years of age who present with painless lower gastrointestinal bleeding without signs of gastroenteritis (diarrhea) or inflammatory bowel disease (diarrhea and abdominal pain) Adults → In adult patients younger than 40 with obscure lower gastrointestinal bleeding