Meckel's diverticulum overview

# Overview
Meckel's diverticulum is a vestigial remnant of the omphalomesenteric duct (also called the vitelline duct) and is the most frequent malformation of the gastrointestinal tract. Meckel's diverticulum was first described by Fabricius Hildanus in the sixteenth century. In 1809, Johann Friedrich Meckel threw light on the embryological origin of Meckel's diverticulum. 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 "Rule of 2s" applies to patients with Meckel's diverticulum and states that it affects approximately 2 percent of the population with a male-to-female ratio of 2:1. It is mostly located about two feet proximal to the ileocecal valve, is approximately two inches in length, and in majority of cases, affects age group <2yrs. In addition, the two most common types of ectopic mucosa found within the diverticulum are the gastric and pancreatic types. Increased prevalence of Meckel's diverticulum is seen in children with umbilical malformations, gastrointestinal tract, neurological and cardiovascular defects. The presentation of Meckel's diverticulum is usually asymptomatic .The hallmark feature in symptomatic patients is the occurrence of painless lower gastrointestinal bleeding. Other symptoms of Meckel's diverticulum arise in complicated cases with features of intestinal obstruction, intussusception, volvulus and perforation. Abdominal examination of patients with Meckel's diverticulum is usually normal, even in patients with gastrointestinal bleeding. Patient develop signs of acute abdomen due to diverticular inflammation or perforation in complicated cases. Laboratory findings are non specific and patients may show volume depletion, features of anemia (such as decreased hematocrit, decreased hemoglobin levels and positive stool guaiac test). A technetium-99m (99mTc) pertechnetate scan is the investigation of choice for the diagnosis of Meckel's diverticulum. This scan detects gastric mucosa; since approximately 50% of symptomatic Meckel's diverticula have ectopic gastric (stomach) cells contained within them. A Meckel's diverticulum containing gastric mucosa manifests as a small rounded area of increased activity in the right lower quadrant, while normal activity simultaneously appears in the stomach. Initially, the medical management of a symptomatic case of Meckel's diverticulum is directed toward management of clinical manifestations of complications. Intravenous lines for fluid and electrolyte therapy, nasogastric decompression for patients with symptoms and signs of intestinal obstruction, proton-pump inhibitors and Aluminum hydroxide for patients with gastrointestinal bleeding are preferred. Surgery is the primary treatment modality in patients with Meckel's diverticula. Absolute indications for resection of a symptomatic Meckel's diverticulum include complications such as hemorrhage, umbilicoileal fistulas, diverticulitis and bowel obstruction. Fibrous band division, diverticulectomy, segmental resection of the diverticulum with end-to-end intestinal anastomosis and wedge resection are the various surgical procedures performed, whenever indicated.

# Historical Perspective
Meckel's diverticulum was first described by Fabricius Hildanus in the sixteenth century. In 1809, Johann Friedrich Meckel threw light on the embryological origin of Meckel's diverticulum.

# Classification
There is no established system for the classification of 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 Meckels 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.

# Causes
Persistence of the vitelline duct due to incomplete involution leads to the formation of Meckels diverticula, the most common congenital abnormality of the small intestine.

# Differentiating Meckel's diverticulum from Other Diseases
The common diseases responsible for lower GI bleeding that must be differentiated from Meckel's diverticulum include diverticulosis, angiodysplasia, hemorrhoids, anal fissures, mesenteric Ischemia,  and colorectal carcinoma. Meckel's diverticulitis is a common complication of Meckel's diverticulum in adults and must be differentiated from other causes of abdominal pain and lower gastrointestinal bleeding such as infective colitis, IBD and acute ischemic colitis.

# Epidemiology and Demographics
Meckel's diverticulum is present in approximately 2% of the population, as per the "Rule of 2s". This rule applies to patients with Meckel's diverticulum and states that it affects approximately 2 percent of the population with a male-to-female ratio of 2:1. It is mostly located about two feet proximal to the ileocecal valve, is approximately two inches in length, and in majority of cases, affects age group <2yrs. In addition, the two most common types of ectopic mucosa found within the diverticulum are the gastric and pancreatic types. Increased prevalence of Meckel's diverticulum is seen in children with umbilical malformations, gastrointestinal tract, neurological and cardiovascular defects.

# Risk Factors
Common risk factors in the development of Meckel's diverticulum include histologic and anatomic features such as length of diverticulum >2cm, presence of ectopic tissue, broad based diverticulum, and attachment of fibrous bands to the diverticulum. Patient age of less than 50 years and the male gender are more susceptible to the development of Meckel's diverticulum.

# Screening
There is insufficient evidence to recommend routine screening for Meckel's diverticulum.

# Natural History, Complications and Prognosis
Meckel's diverticulum is mostly seen in male children (mostly <2 years of age). One fourth of untreated cases of Meckel's diverticulum may develop complications such as intestinal obstruction, hemorrhage, diverticulitis, bowel ischemia, and necrosis. Hemorrhage is the most common complication in patients with Meckel's diverticulum. Bleeding in patients may be minimal, recurrent or massive and shock-producing. The rate of bleeding is assessed based on quantity of blood lost in the stools, appearance of the material passing through the rectum and hemodynamic state of the patient. Depending on the extent of the symptom progression at the time of diagnosis, the prognosis may vary. However, the prognosis is generally regarded as excellent in cases where symptomatic Meckel's diverticulum is treated in a timely manner. Complete recovery may be expected with surgery in majority of the cases.

# Diagnosis

## History and Symptoms
The presentation of Meckel's diverticulum is usually asymptomatic .The hallmark feature in symptomatic patients is the occurrence of painless lower gastrointestinal bleeding. Other symptoms of Meckel's diverticulum arise in complicated cases with features of intestinal obstruction, intussusception, volvulus and perforation. The age of presentation for approximately half of all patients is less than 10 years of age. Patients may also develop symptoms of diverticular inflammation (ie, Meckel's diverticulitis) which has a presentation similar to acute appendicitis.

## Physical Examination
Patients with Meckel's diverticulum usually appear normal on physical examination. Abdominal examination of patients with Meckel's diverticulum is usually normal, even in patients with gastrointestinal bleeding. Patient develop signs of acute abdomen due to diverticular inflammation or perforation in complicated cases. These signs include Abdominal distention, abdominal tenderness, rebound tenderness and guarding.

## Laboratory Findings
Laboratory findings are non specific and do not distinguish Meckel's diverticulum from other sources of gastrointestinal bleeding. Laboratory findings in patients may show volume depletion, features of anemia (such as decreased hematocrit, decreased hemoglobin levels and positive stool guaiac test).

## Other Imaging Findings
A technetium-99m (99mTc) pertechnetate scan is the investigation of choice for the diagnosis of Meckel's diverticulum. This scan detects gastric mucosa; since approximately 50% of symptomatic Meckel's diverticula have ectopic gastric (stomach) cells contained within them. A Meckel's diverticulum containing gastric mucosa manifests as a small rounded area of increased activity in the right lower quadrant, while normal activity simultaneously appears in the stomach.

## Other Diagnostic Studies
Diagnostic studies such as colonoscopy, double-balloon enteroscopy, laproscopy, laparotomy may help in the detection of symptomatic and asymptomatic Meckel's diverticula. Screenings for bleeding disorders may be performed to rule out other sources of bleeding.

# Treatment

## Medical Therapy
Initially, the medical management of a symptomatic case of Meckel's diverticulum is directed toward management of clinical manifestations of complications. Intravenous lines for fluid and electrolyte therapy, nasogastric decompression for patients with symptoms and signs of intestinal obstruction, proton-pump inhibitors and Aluminum hydroxide for patients with gastrointestinal bleeding are preferred. The process of initial resuscitation in patients with lower gastrointestinal bleeding due to Meckel's diverticulum) is similar to the steps followed in any case of lower GI bleeding.

## Surgery
Surgery is the primary treatment modality in patients with Meckel's diverticula. Asymptomatic patients are treated in the presence of features such as narrow diverticular mouth, fibrous bands, ectopic gastric tissue, diverticular length >2cm, stasis, narrow neck, intramural pathology, thickening and inflammation of the diverticulum. On the other hand, absolute indications for resection of a symptomatic Meckel's diverticulum include complications such as hemorrhage, umbilico ileal fistulas, diverticulitis and bowel obstruction. Fibrous band division, diverticulectomy, segmental resection of the diverticulum with end-to-end intestinal anastomosis and wedge resection are the various surgical procedures performed, whenever indicated.

## Prevention
There are no established measures for the primary prevention of Meckel's diverticulum. Secondary prevention involves management of post operative complications of Meckel's diverticula include ileus, intra-abdominal abscess formation, pulmonary embolism, anastomotic leakage and intestinal obstruction due to postoperative adhesions. Treatment of complications such as intra-abdominal abscess and intestinal obstruction due to stenosis or adhesions is mainly surgical. The management of ileus is mainly supportive and the patient is kept NPO with nasogastric suction and parenteral feeds. Electrolyte levels need to be monitored and pharmacotherapy such as lactulose may also be administered to patients.