Diverticulum of meckel

true diverticulum of the ileum, containing the three layers of the bowel wall.

Diverticulum of Meckel results if the omphalomesenteric or vitelline duct, which connects the primitive midgut with the yolk sac fails to obliterate which should normally occur at 78 weeks of gestation. Meckels diverticulum is found in 23% of individuals at autopsy and constitutes the most common congenital anomaly of the gastrointestinal tract. The duct remnant may persist as a diverticulum which at its dome may be connected to the umbilicus by a fibrous band (Fig.1) or it may remain unattached to the umbilicus. If the vitelline duct may remain attached and a patent fistula may be present.

Heterotopic tissue is present in the diverticulum in 50% of cases: most frequent are gastric mucosa or pancreatic tissue or an association of both. More rarely colon mucosa or hepatobiliary tissue is found. The site of origin of the diverticulum is on the antimesenteric border of the ileum and is located within 100 cm from the ileocaecal valve.

Symptoms due to Meckels diverticulum are due to complications and are observed mainly in children, less frequently in adults. These complications include bleeding, which is mostly related to ulceration of ectopic gastric mucosa and intestinal obstruction, which is due either to intussusception of the diverticulum into the bowel lumen (inverted diverticulum) or to volvulus around a fibrous band. Single or multiple enteroliths in the diverticulum may occur in up to 10% of cases. Most are only peripherally calcified. Stone ileus due to extrusion of the enterolith into the lumen of the bowel has been described. Extrusion of the diverticulum into an inguinal hernia may occur and is known as hernia of Littre.

Radiological features

The diagnosis of Meckels diverticulum is notoriously difficult and remains a continuing challenge for the radiologist.

Scintigraphy can be useful in order to visualize a bleeding diverticulum of Meckel particularly in children because in this age group bleeding is frequently due to ulceration of gastric mucosa present within the diverticulum. Scintigraphy is useful to identify the bleeding but it will not identify the source of the bleeding as a Meckel diverticulum unless a subsequent specific scintigraphic examination demonstrates the presence of ectopic gastric mucosa.

Plain radiography may show typical features of mechanical bowel obstruction. Moreover, an enterolith or, if the diverticulum is very large, an abnormal gas shadow may point to the lesion.

Ultrasonography may show an obstructed and dilated fluid-filled diverticulum. Isolated cases of intussusception of a Meckels diverticulum diagnosed by ultrasound have been reported as a target-like mass containing a central area of increased echogenicity but generally ultrasound cannot make an important contribution to the diagnosis. Although the conventional small bowel barium series is considered mostly as not being able to routinely detect Meckels diverticulum in a high percentage of patients, the lesion may be demonstrated if careful fluoroscopic technique is applied. The inability to adequately distend and separate the bowel loops and the failure to visualize the mucosal fold pattern of the distal ileum are common in barium follow-through studies. In addition the wide neck and the diverticulums peristaltic activity tend to keep the diverticulum empty or only partially filled, often preventing a correct diagnosis. Small bowel enema will typically depict the diverticulum as a single, contrast filled blind outpouching arising on the antimesenterial border with a broad base (Fig.2). It may have an ovoid, a tubular or a bilobed shape. The confirmation of the Meckel origin of the diverticulum rests on the visualization of its fold patterns, especially at the site of its attachments to the small bowel. A "triradiate" fold pattern in which higher rate of bleeding may be necessary.

In patients with inconclusive imaging findings and who are not actively bleeding angiography is still useful because it may detect vascular anomalies that are suggestive for Meckels diverticulum. Angiography will typically show a long nonbranching "vitelline" artery originating as an ileal branch of the superior mesenteric artery and directing towards the right lower quadrant. It supplies a network of tortuous and irregular small vessels, arranged in a "basket" pattern. Less frequently the Meckels diverticulum is supplied by branches originating from the ileocolic artery which makes the differential diagnosis with bleeding causes related to the caecum and ascending colon more difficult. Superselective injection and the use of epinephrin to induce selective constriction of the normal splanchnic circulation are recommended in order to obtain an optimal visualization of the site of the lesion. In case of severe bleeding transcatheter embolization should be considered in order to have the subsequent surgical procedure performed under more stable conditions.

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