Meckel diverticulum is the most common congenital anomaly of the gastrointestinal tract, secondary to the failure of regression of the onphalomesenteric duct. It is defined as a blind ending tubular structure originating from the antimesenteric end of the distal ileum. Contains all of the intestinal layers (mucosa, muscular layers and serosa), corresponding to a true diverticulum [1,3].
Location, frequency and complication rates of Meckel diverticula differ among different sources and publications. In an effort to sum up all of the information, the "rule of the 2s" has been described [1,2,4,5,13]:
- Meckel diverticulum is present in 2% of the population.
- It is up to 2 inches (5 cm) long.
- It is located up to 2 feet (50-60 cm) proximal to the ileocecal valve.
- 2/3 of them present with ectopic mucosal tissue.
- The ectopic mucosal tissue consists most likely of 2 types: gastric (62%) and pancreatic (6%).
- 2% of Meckel diverticula become symptomatic.
- Most of the complications occur in the first 2 years of life.
As it can be deduced from the "rule of the 2s", even if 1 in 50 people have Meckel diverticulum, only a few of them (approximately 0,04% of the population) will eventually develop symptoms related to this congenital anomaly.
Though the prevalence of Meckel diverticulum does not differ significantly between males and females, a higher complication risk in male patients has been described. Symptoms and complications related to Meckel diverticula tend to be mild to moderate, with a higher risk for severe complications reported in early childhood [2-5,8-10].
Even if the presence of ectopic mucosal tissue is frequent, it should be noted that the presence of gastric (frequently associated to gastrointestinal bleeding) or pancreatic mucosa (associated to intestinal intususception) increases the risk of complication development[3,6].
The normal sonographic (US) features of the uncomplicated Meckel diverticulum are [2-10] (Fig. 15-17):
- Blind ending fluid and/or air-filled tubular structure.
- Commonly located in the right lower quadrant (but can lie elsewhere in the abdomen).
- Thick walled.
- Presenting a normal hyperechoic intestinal mucosa.
- Connected to the normal peristaltic small bowel.
- Arising from the antimesenteric bowel wall.
- Some of them may show an enterolith (hyperechoic with posterior acoustic shadowing).
Other imaging techniques, such as abdominal CT scan or abdominal MRI, may fail in the detection of the uncomplicated Meckel diverticulum.
A Nuclear Medicine imaging technique, 99mTc-pertechnetate gammagraphy, might be useful in the detection of ectopic gastric mucosa, as the radiotracer is only uptaken by the mucin secretory cells of the stomach .