Wilhelm Fabricius Hildanus, a German surgeon, first described the presence of a small bowel diverticulum in 1598. However, the diverticulum is named for Johann Friedrich Meckel, a German anatomist, who further described the anatomy and embryology in 1809. Meckel diverticulum is a remnant of the embryologic vitelline (omphalomesenteric) duct that connects the fetal gut with the yolk sac and normally involutes between the fifth and seventh weeks of gestation. Failure of duct regression results in a variety of abnormalities arising from persistence of the remnant ( Fig. 38.1 ). The most common anomaly (90%) is the classic Meckel diverticulum. It is a true diverticulum, consisting of all normal layers of the bowel wall. Clinical symptoms and complications can arise from small bowel obstruction, bleeding, inflammation, umbilical abnormalities, or neoplasia.
Drawings illustrating morphologies of various omphalomesenteric (vitelline) duct remnant structures. (A) Simple Meckel diverticulum. (B) Meckel diverticulum with fibrous cord attached to umbilicus. (C) Patent omphalomesenteric duct with umbilico-ileal fistula. (D) Cyst within the vitelline duct remnant. (E) Fibrous cord alone without diverticulum or cyst. (F) Fibrous cord with persistent vitelline artery.
From Moore KL. The Developing Human . Philadelphia: WB Saunders; 1988.
Epidemiology
The true incidence of Meckel diverticulum is unknown, because most patients are asymptomatic. Although the incidence is commonly estimated at approximately 2%, a systematic review of autopsy studies found an incidence of 1.2%. The incidence may be increased in patients with major anomalies of the umbilicus, alimentary tract, nervous system, or cardiovascular system. An estimated 4%–6% of patients with Meckel diverticulum will become symptomatic, and the risk of developing symptoms decreases with age. A report based on data from the Pediatric Health Information System database found that 53% of Meckel diverticulectomies are performed before 4 years of age, with a male-to-female ratio of 2.3:1 overall and 3:1 in symptomatic patients. The commonly cited “rule of 2s” regarding the diverticulum is: occurs in 2% of the population, has a 2:1 male-to-female ratio, usually discovered by 2 years of age, located 2 ft (60 cm) from the ileocecal valve, commonly 2 cm in diameter and 2 inches (5 cm) long, and can contain two types of heterotopic mucosa. Gastric is the most common type of heterotopic mucosa, followed by pancreatic ( Fig. 38.2 ). More rarely, it may contain duodenal, colonic, or endometrial tissue.
This laparoscopic view shows a long Meckel diverticulum emanating from the antimesenteric border of the ileum. This is a true diverticulum and contains ectopic mucosa at the tip of the diverticulum ( arrow ).
Clinical Presentation
A variety of symptoms can develop depending on the configuration of the remnant structure and the presence of ectopic mucosa. The three most common presentations in children are intestinal bleeding (30%–56%), intestinal obstruction (14%–42%), and diverticular inflammation (6%–14%). Other less common signs include a cystic abdominal mass and a newborn with an umbilical fistula resulting from a patent vitelline duct ( Fig. 38.3 ). A Littré hernia refers to a Meckel diverticulum found incarcerated in a hernia, which may be located at the inguinal, femoral, umbilical, or Spigelian sites. In adults, especially the elderly, neoplasia can develop within the Meckel diverticulum. Carcinoid is the most common tumor, but other malignancies include adenocarcinoma, leiomyosarcoma, gastrointestinal stromal tumors, and lymphoma. Neonatal presentation of a Meckel diverticulum is uncommon but can occur due to perforation, umbilical fistula, or obstruction.
This neonate was born with an obvious patent omphalomesenteric duct. (A) Meconium was seen to emanate from the stoma. (B) A circumumbilical incision was made, and the duct ( arrow ) was dissected to its connection with the ileum. (C) The duct was amputated from the ileum and the umbilical incision closed. The patient recovered uneventfully.
Bleeding
Episodic painless rectal bleeding in a young child is the classic presentation of a bleeding Meckel diverticulum. A Meckel diverticulum accounts for nearly 50% of all lower gastrointestinal bleeding in children. The stool may be bright red, dark or maroon red, or less commonly tarry. The bleeding is often associated with anemia, and many children will require transfusion, though life-threatening hemorrhage is rare. Physical examination is typically unremarkable. The bleeding may also be slow and not clinically evident, presenting solely as unexplained anemia. Thus, any child presenting with hemoglobin-positive stools and chronic anemia should be evaluated for a Meckel diverticulum.
Bleeding is generally attributed to the presence of heterotopic gastric mucosa, present in 80%–100% of Meckel diverticula that bleed. Gastric acid secretion results in ulceration of the adjacent normal ileal mucosa, generally within a few millimeters of the gastric mucosa. While Helicobacter pylori is associated with many ulcers in the duodenum and stomach, studies have shown that H. pylori is rarely present in a bleeding Meckel diverticulum. ,
Obstruction
A Meckel diverticulum can cause intestinal obstruction through several mechanisms, but most commonly intussusception or volvulus. The diverticulum can act as a lead point for an obstructing ileo-ileal or ileocolic intussusception. A volvulus can occur if the diverticulum is tethered to the umbilicus by a fibrous cord of vitelline duct remnant. An internal hernia can result due to a mesodiverticular artery, coursing from the base of the mesentery to the diverticulum, under which the small bowel becomes entrapped and incarcerated ( Fig. 38.4 ). Other rare obstructing mechanisms include an incarcerated Littré hernia and a long diverticulum that may knot on itself or twist around its base.
An internal hernia can result from a band that often contains the mesodiverticular artery and courses from the base of the mesentery to the diverticulum, under which the small bowel becomes entrapped and incarnated (A). In (B) the internal hernia has been reduced and the band containing the mesodiverticular artery is seen. In (C) the large Meckel diverticulum is seen. In (D) the mesodiverticular band has been divided and the diverticulum has been exteriorized through the umbilical incision. The diverticulectomy was performed, and the resulting enterotomy was closed in two layers (E) . The appearance of the abdomen following closure of the incisions in seen in (F) .
Patients presenting with obstruction will usually demonstrate typical signs of crampy abdominal pain, bilious vomiting, and obstipation. In the setting of intussusception, the child may pass currant jelly stools and physical examination may demonstrate a palpable abdominal mass. If a volvulus progresses to ischemia, the patient will develop signs of peritonitis and can present in extremis.
Inflammation
Inflammation of the diverticulum is often attributed to the presence of heterotopic gastric or pancreatic tissue. Obstruction of the diverticular lumen can also produce inflammation, similar to the mechanism for appendicitis. Luminal obstruction can occur due to stasis of enteric contents within the diverticulum, the presence of an enterolith or foreign body, or even parasitic infections. Meckel diverticulitis is often misdiagnosed as appendicitis due to similar presenting symptoms, including periumbilical pain that may be associated with nausea, vomiting, and fever. The point of maximal tenderness on physical examination may migrate within the abdomen. Given the possibility of misdiagnosis, the intraoperative finding of a normal appendix in a child suspected of having appendicitis should lead to a careful search for a Meckel diverticulum. Due to variability in the location of the diverticulum, at least 5 ft of distal small bowel should be examined, starting at the terminal ileum and working proximally. Meckel diverticulitis can also result in perforation, intraabdominal abscess, and obstructive signs and symptoms.
Diagnosis
In patients presenting with obstruction or inflammation, the diagnosis of a Meckel diverticulum is not usually definitively determined preoperatively. In some cases, a preoperative computed tomography scan or ultrasound (US) may find an inflamed midline mass with a normal appendix, suggesting the correct diagnosis. In a child older than 5 years of age who has not undergone an abdominal operation and presents with signs and symptoms of small bowel obstruction, a Meckel diverticulum should be strongly considered as the etiology. The diagnosis of intussusception is often confirmed by US or air enema, but rarely identifies a pathologic lead point, such as a Meckel diverticulum. Air enema may reduce the ileocolic portion of the intussusception, but often the ileo-ileal component is not successfully reduced. If it is reduced, symptoms will often recur. When present, the diverticulum will be discovered either intraoperatively once reduced completely or upon examination of the resected segment of intestine.
In patients presenting with lower gastrointestinal bleeding, preoperative studies can often determine the etiology. In addition to a Meckel diverticulum, the differential diagnosis for rectal bleeding includes anal fissure, intestinal polyps, inflammatory bowel disease, intestinal duplications, hemangiomas, and arteriovenous malformations. A complete history and physical examination can help exclude some potential bleeding sources. Placement of a nasogastric tube can exclude an upper gastrointestinal source as well. The preferred radiologic test is technetium-99m pertechnetate radionuclide scintigraphy (“Meckel scan”). This nuclear medicine imaging study relies on the fact that most bleeding Meckel diverticula contain heterotopic gastric mucosa. The intravenously injected technetium-99m pertechnetate is taken up and secreted by the tubular gland cells of gastric mucosa. Scintigraphy can then visualize focal accumulation of the tracer in the diverticulum ( Fig. 38.5 ). Active bleeding is not required to achieve a positive result with scintigraphy, unlike angiography or a tagged red blood cell scan.
Technetium-99m pertechnetate scan of a patient with a Meckel diverticulum. Note the blush ( arrow ) above the bladder.
Courtesy Kyo Lee, MD.
Meckel scan has a sensitivity of 89%–100% in children presenting with bleeding symptoms and a specificity of over 95%. False negatives can occur if the diverticulum contains no or very little gastric mucosa, if it is lying low in the pelvis and obscured by the bladder, or in setting of bowel irritation or brisk bleeding resulting in rapid washout of the secreted tracer. Other types of ectopic mucosa will not take up the radiotracer. False positives can also occur as a result of intestinal duplications, bowel obstruction or inflammation, intussusception, arteriovenous malformations, ulcers, and some neoplasms. Accuracy can be improved with the use of pharmacologic adjuncts, such as histamine-2 blockers to inhibit release of the tracer from the mucosal cells and glucagon to decrease peristalsis and washout of the secreted tracer. In patients with high clinical suspicion but a negative or equivocal scan, repeat scintigraphy may have utility, as one study reported 30% positivity on a second scan. Since a negative scan does not definitively exclude the possibility of a Meckel diverticulum, several authors have recommended diagnostic laparoscopy for definitive evaluation, especially in cases with anemia and a high clinical suspicion for a bleeding diverticulum. ,
Other tests useful in the evaluation of intestinal bleeding include mesenteric angiography and a technetium-99m tagged red blood cell scan. Angiography is limited to patients with significant acute hemorrhage as it is invasive and requires active bleeding of at least 0.5 mL/min. A tagged red cell scan requires bleeding of at least 0.1 mL/min and may be more sensitive but less specific for localizing the bleeding source. Upper and lower endoscopy will not allow visualization of a Meckel diverticulum, but these tests are helpful to evaluate for other disorders that may produce rectal bleeding. Wireless capsule endoscopy and double-balloon enteroscopy techniques have been utilized to identify a Meckel diverticulum. Although these modalities are not used regularly, they may be helpful when all other tests have failed to identify the site of bleeding.
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