Meckel diverticulum represents a true diverticulum of the ileum containing all 3 layers of the bowel wall. Meckel diverticulum develops if the omphalomesenteric or vitelline duct, which connects the primitive midgut with the yolk sac, fails to obliterate, which normally occurs at 7-8 weeks of gestation. Heterotopic tissue, including gastric mucosa and pancreatic tissue, is present in 50% of patients.
See the images of Meckel diverticulum below.
Symptoms resulting from a Meckel diverticulum occur because of complications and are more frequent in children than in adults and include hemorrhage and intestinal obstruction. Hemorrhage is usually due to erosion of adjacent ileal mucosa by acid produced by ectopic gastric mucosa. Intestinal obstruction is most often due to volvulus about the Meckel diverticulum or intussusception with the diverticulum as the lead point. 
Plain radiography, barium studies, angiography, computed tomography (CT), ultrasonography, and scintigraphy all play complementary roles in the diagnosis of the complications of Meckel diverticulum. The diagnosis is notoriously difficult and remains a continuing challenge for the radiologist. [4, 5, 6, 7, 8, 9, 10] In all imaging modalities, findings of Meckel diverticulum are nonspecific. Most Meckel diverticula are diagnosed during surgery or autopsy, with imaging playing a secondary role. The most sensitive technique is scintigraphy, and various modifications to imaging techniques have been devised to improve sensitivity. Ultrasonography and CT are improving and can help in making an anatomic diagnosis. [11, 12, 13, 14]
Plain radiographs may demonstrate appearances typical of an intestinal obstruction. [1, 4, 15] If the diverticulum is distended, a gas-filled viscus seen in the right iliac fossa or the mid abdomen may provide a clue to the diagnosis. The presence of an enterolith may further support the diagnosis. (See the image below.)
Findings on plain abdominal radiographs are nonspecific. A conventional small-bowel barium examination has a low yield because the diverticula fill transiently and surrounding loops of small bowel tend to overlap and obscure the diverticula. 
Although a conventional small-bowel barium meal is usually not helpful in routinely depicting Meckel diverticulum in many patients, the anomaly can be detected if careful technique is applied. [1, 16] Some limitations encountered by using barium series are the overlapping of small bowel loops, the inability to achieve adequate distention, and the failure to adequately depict the mucosal pattern in the distal ileum. The yield improves with meticulous technique and spot compression imaging.
The diagnostic yield is also improved with enteroclysis. Enteroclysis can detect as many as 50% of Meckel diverticula. Retrograde small-bowel examination probably helps in detecting most Meckel diverticula because of the distal location. Barium enema study probably reveals most Meckel diverticula when sufficient reflux is achieved into the terminal ileum. 
Typically, the diverticulum is depicted as a contrast-filled outpouching, 0.5 to 20 cm long, that is located on the antimesenteric border of the ileum and has a junctional-fold pattern. The site of origin of a Meckel diverticulum rests on the demonstration of its junctional-fold pattern at the site of attachment. The characteristic junctional-fold appearances are a triradiate fold pattern, in which the loops are collapsed, and a mucosal triangular plateau, in which the loops are distended.
When perforation is a complication, plain abdominal and upright chest radiographs may reveal features of a pneumoperitoneum.
An inverted Meckel diverticulum without an intussusception, which occurs in 20% of patients, appears as an elongated, smoothly marginated, clublike intraluminal mass parallel to the long axis of the ileum. Rarely, a gastric rugal pattern, intraluminal filling defects, and mucosal irregularity are identified. These are suggestive of ectopic gastric mucosa.
The neck of the diverticulum may become occluded by inflammation, which makes it difficult for the diverticulum to fill with barium; thus, a false-negative diagnosis may occur. Similarly, if the neck of the diverticulum is wide at the point where peristaltic activity tends to keep the diverticulum empty or partially filled, the result is a false-negative finding.
Demonstration of Meckel diverticulum does not necessarily mean that the diverticulum is the cause of symptoms. A barium examination involves simply filling the diverticulum with barium. In an actively bleeding patient, barium examination does not show whether the bleeding originates in the diverticulum. Rarely, a false-positive diagnosis may occur with acquired small-bowel diverticula (occurs in patients >40 y) and bowel duplications.
CT rarely is used as a primary imaging modality in patients in whom Meckel diverticulum is suspected. Most diagnoses made by using CT scans are incidental. An inverted Meckel diverticulum associated with an intussusception may be revealed as an intraluminal mass composed of a central area of fat attenuation representing the entrapped mesenteric fat of the inverted diverticulum, surrounded by a thick collar of soft-tissue attenuation.  Intussusception from other causes may appear similar to intussusception associated with Meckel diverticulum on CT scans. [11, 13]
Ultrasonography is usually the first investigation used in young patients presenting with abdominal pain because it is noninvasive, but its role in evaluating gastrointestinal hemorrhage is limited. Occasionally, intussusception secondary to Meckel diverticulum has been diagnosed by using sonograms. However, the sensitivity and specificity of ultrasonographic examination generally is low.
Sonographically, Meckel diverticulum may be identified when complications occur, such as a fluid-filled overdistended tube connected to the umbilicus. This tubular structure can be differentiated from an inflamed appendix because the former is larger and is located farther from the cecum. Two target signs of different sizes have been described in a double intussusception of the Meckel diverticulum into the ileum and the ileum into the colon.
The mucoid cells of the gastric mucosa secrete chloride into the intestinal lumen. Excretion does not depend on the presence of the parietal cells. Technetium-99m (99m Tc) pertechnetate behaves in a manner that is analogous to halide anions (eg, chloride, iodide). The mucoid surface cells of gastric mucosa, whether located normally or ectopically, actively accumulate and secrete pertechnetate into the intestine. This is the basis for detecting ectopic gastric mucosa in symptomatic Meckel diverticulum. [5, 6, 9, 10, 12, 14]
See the nuclear images below.
Patient preparation is important to optimize results of this technique. This includes avoiding certain procedures, such as administration of cathartics (drugs that irritate the gastrointestinal tract), contrast-enhanced studies, endoscopy, and use of enemas for 48 hours prior to the procedure. The quality of images is poor in patients who have received perchlorate or atropine.
The administration of certain drugs prior to scintigraphy improves results. These drugs include pentagastrin (which stimulates radionuclide uptake), cimetidine (which inhibits release of pertechnetate from the ectopic mucosa), and glucagon (which inhibits peristalsis). Because pentagastrin also increases motility, it may be most useful when used in conjunction with glucagon.
False-positives and false-negatives
Scintigraphy has an accuracy of 83-88%, a sensitivity of more than 85%, and a specificity of more than 95%. Sensitivity drops after adolescence. False-positive results have been reported for a variety of reasons, including faulty technique, uptake at other sites of ectopic gastric mucosa (eg, in a gastrogenic cyst), and some enteric duplications. Occasionally, false-positive results are observed in a normal small bowel.
Vascular anomalies are a further source of false-positive findings, such as aneurysms, arteriovenous malformations, hemangiomas, and hypervascular tumors. Because99m Tc pertechnetate is excreted by the kidneys, horseshoe kidneys, caliceal diverticulum, and urinary tract obstruction resulting from a variety of causes may cause false-positive scans. False-positive scans also may occur with a variety of bowel ulcerations, inflammations, and obstructions, including those due to duodenal ulcers, ulcerative colitis, Crohn disease, appendicitis, laxative abuse, intestinal obstruction, intussusception, and volvulus. These false-positive results are thought to be due to hyperemia caused by these conditions.
Careful attention to the timing of appearance of abnormal accumulations of pertechnetate can aid in distinguishing the false-positive causes from those due to ectopic gastric mucosa. The accumulations of pertechnetate due to hyperemia appear early in the study and tend to fade over time. The accumulations in ectopic gastric mucosa appear at, or nearly simultaneous with, the stomach and increase in intensity in parallel with the stomach. Lateral and oblique views are often helpful in differentiating the anterior location of a diverticulum from the posterior location of urinary activity.
False-negative scans may occur if the gastric mucosa mass within the diverticulum is insufficient or if intraluminal scintigraphic activity is diluted as a result of brisk hemorrhage or bowel hypersecretion.
Despite the reported sensitivity of radionuclide scanning, controversy remains regarding its use. Some clinicians believe that radionuclides have a limited role in the diagnosis of Meckel diverticulum and that imaging of all types should be replaced by laparoscopy, which offers the additional possibility of laparoscopic resection of a Meckel diverticulum. However, when used appropriately with meticulous technique in the appropriate age group, scintigraphy remains the best technique available for the diagnosis of a Meckel diverticulum.  The radiation dose to the patient is small and acceptable. Laparoscopy is more invasive and poses a risk of morbidity.
In patients presenting with acute gastrointestinal tract bleeding from a Meckel diverticulum, superior mesenteric angiograms may demonstrate not only the site of bleeding by focal contrast agent extravasation but also the cause of bleeding. Demonstration of the vitelline artery, which is an anomalous end branch of the superior mesenteric artery, is pathognomonic.
The vitelline artery originates as an ileal branch of the superior mesenteric artery; this vessel is nonbranching and directed toward the right lower quadrant of the abdomen. This artery supplies the diverticulum via a network of tortuous and irregular small vessels likened to a basket-weave pattern. Superselective technique and the use of epinephrine are recommended to cause selective constriction of the normal splanchnic circulation for optimal depiction of the site of the lesion. 
Angiography has an accuracy of 59%. Bleeding at a rate of 2-3 mL/min is required in adults for angiographic detection; higher rates of hemorrhage may be required in children for angiographic detection. Rarely, a Meckel diverticulum is supplied by branches arising from the ileocolic artery, which makes it more difficult to differentiate the causes of bleeding related to the cecum and ascending colon.
When diagnostic angiography images depict severe gastrointestinal tract bleeding, superselective embolization should be considered so that surgery can be performed under stable conditions. [3, 18, 19]