Meckel's diverticulum
Meckel's diverticulum is a congenital anomaly of the gastrointestinal tract resulting from the persistence of the vitelline duct, which normally disappears during embryonic development. Occurring in approximately 2% of the population, this condition often remains asymptomatic. However, when symptoms do arise, they can include painless rectal bleeding in children, which is linked to the presence of heterotopic stomach tissue that can cause ulcers, or abdominal pain and obstruction in adults. The diagnosis of Meckel's diverticulum can be challenging, typically requiring advanced imaging techniques like laparoscopy or technetium scans. Surgical intervention is generally the treatment of choice for symptomatic cases, especially when complications such as bleeding or obstruction occur. Despite being the most common congenital malformation of the gastrointestinal tract, Meckel's diverticulum is often underdiagnosed due to its nonspecific symptoms. Understanding its historical context, dating back to discoveries in the late 16th century, can provide insight into its medical significance today.
Meckel's diverticulum
Disease/Disorder
Also known as: Meckel diverticulum
Anatomy or system affected: Gastrointestinal system, intestines
Definition: A pouch on the wall of the lower part of the intestine that persists from embryonic development.
Key terms:
heterotopic tissue: tissue formed in an abnormal location
midgut: the portion of the embryonic gut from which most of the intestines develop
primitive gut: a tubular structure in the embryo that differentiates into the gastrointestinal tract and its associated structures
vitelline duct: a narrow tube that joins the midgut to the yolk sac in the early embryo
yolk sac: a sac-like membrane outside the embryo that serves as the early site for the formation of blood and blood vessels and is connected to the midgut by the vitelline duct
Causes and Symptoms
By the fourth week of embryonic development, an extraembryonic membrane known as the yolk sac (or umbilical vesicle) has formed. At this time, the embryo, which has formed incipient nervous and circulatory systems, lies above the yolk sac. Inside the embryo is a tube that eventually becomes the gastrointestinal tract (primitive gut). The primitive gut consists of three parts; the foregut, midgut, and hindgut. The foregut forms the pharynx, lower respiratory system, esophagus and stomach, the liver and its associated structures, the pancreas, and the first part of the small intestine. The midgut forms the rest of the small intestine and over half the colon, and the hindgut forms the rest of the colon. Initially, the midgut opens directly into the yolk sac, but as development progresses, the front and back of the embryo bend downwards, constricting the connection of the midgut to the yolk sac. By the sixth week of gestation, the link between the midgut and the yolk sac has narrowed to a slim stalk known as the vitelline duct, and by the seventh week, all connections between the midgut and the yolk sac have completely disappeared.
Occasionally, the vitelline duct persists and produces various structural abnormalities, the most common of which is a blind pouch that bulges from the small intestine known as Meckel’s diverticulum (MD). In over half the cases, Meckel’s diverticula harbor out-of-place or heterotopic gastrointestinal tissues; most commonly stomach tissue, or less frequently pancreatic tissue, or stomach combined with pancreatic tissue, and even less frequently, upper small intestinal, large intestinal, or even liver tissue.
MD occurs in 2 percent of the population, but the vast majority of cases are asymptomatic. Children who do show symptoms most commonly experience rectal bleeding (hematochezia). Acid secreted by heterotopic stomach tissue erodes the intestinal lining and produces bleeding ulcers. This rectal bleeding tends to be painless and starts and stops on its own. However, in those patients who do suffer pain, their symptoms can mimic those of appendicitis.
Adults rarely show rectal bleeding, but more commonly experience intestinal obstruction as a result of MD wrapping around the intestine (incarcerated) or inverting and internally blocking it. In cases of intestinal obstruction, the most common symptoms include abdominal pain, tenderness, distention, and vomiting. In older patients, MD may become clogged with food and become infected and inflamed (diverticulitis). In this case the symptoms include diffuse abdominal tenderness and pain with distention.
Treatment and Therapy
Diagnosing MD represents a challenge, and it has been said that “MD is frequently suspected, often looked for and seldom found.” Laparoscopy remains one of the best ways to diagnose MD. Laparoscopy uses a thin, lighted tube (laparoscope) that is inserted through a small incision in the abdomen to examine the organs. MD appears as a small pouch extending from the small intestine, about two feet from the junction between the small and large intestines (ileocecal valve). An alternative method for MD diagnosis uses a radioactive compound that concentrates in stomach tissue called technetium-99m pertechnate. Technetium scans are very accurate in children, but less accurate in adults. Computerized tomographic scans can effectively detect Meckel’s diverticulitis, but not uninfected MD.
The treatment of choice for symptomatic MD is surgery. For patients with bleeding, incarcerated or obstructed intestines, laparoscopic removal of Meckel’s diverticulum and the adjacent intestine (small bowel resection) cures the patient. Meckel’s diverticulitis is treated with antibiotics such as clindamycin (Cleoncin), gentamicin (Gentacidin or Garamycin), or cefotetan (Cefotan).
Patients who bleed excessively may become anemic. Severe anemia may require a blood transfusion, but in most cases taking iron and folic acid supplements can restore normal hemoglobin levels and red blood cell numbers.
Five percent of all complicated cases of MD contain malignant tissue and should be referred to an oncologist.
Perspective and Prospects
The description of MD dates to 1598 by Fabricus Hildanus. Later, the German surgeon Lavater reported blind pouches that extended from the lower part of the small intestine (ileum) in 1671. In 1707, Ruysch augmented Lavater’s anatomical descriptions by providing accurate illustrations of MD. In the eighteenth century, Morgagni correctly discerned that MD resulted from structures that persisted from human development, but the precise embryonic structures eluded him. However, in 1809, Johann Friedrich Meckel examined twenty-two different pediatric cadavers and identified the vitelline duct (also known as the omphalomesenteric duct) as the persistent structure that causes MD. For this reason, MD is named after Meckel in his honor.
MD is the most common congenital malformation of the gastrointestinal tract, but because it tends to produce rather nonspecific symptoms, properly diagnosing it remains the greatest challenge facing clinicians with regard to this condition.
Bibliography
Longstreth, George F. “Meckel’s Diverticulum.” MedlinePlus. US Natl. Lib. of Medicine, Natl. Inst. of Health, 8 Oct. 2012. Web. 18 Mar. 2015.
Moore, Keith L., T. V. N. Persuad, and Mark G. Torchia. Before We Are Born: Essentials of Embryology and Birth Defects. 8th ed. Philadelphia: Elsevier/Saunders, 2012.
Sadler, Thomas W. Langman's Medical Embryology. 12th ed. Philadelphia: Lippincott Williams & Wilkins, 2011.
Safer, Diane A. “Meckel’s Diverticulum.” Health Library. EBSCO, Aug. 2014. Web. 18 Mar. 2015.
Uppal, Kiranjit, R. Shane Tubbs, Petru Matusz, Kitt Shaffer, and Marios Loukas. “Meckel’s Diverticulum: A Review.” Clinical Anatomy 24, no. 4 (May 2011): 416–422.