Meckel Diverticulum Imaging
Meckel diverticulum represents a true diverticulum of the ileum containing all 3 layers of the bowel wall. Meckel diverticulum develops if the omphalomesenteric (vitellointestinal 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. Generally, a Meckel diverticulum ranges from 1 to 12 cm in length and is found 45-90 cm proximal to the ileocecal valve. It frequently contains heterotopic tissue; when it does, gastric mucosa accounts for 50%. The so called “rules of 2” states that the Meckel diverticulum occurs in about 2% of the population, is about 2 inches in length, is usually located within 2 feet of the ileocecal valve, and usually presents before 2 years of age. [1, 2]
Technetium-99m pertechnetate scintigraphy, commonly known as Meckel scan, is considered to be the modality of choice to evaluate patients with suspected Meckel diverticulum, based on its diagnostic accuracy of approximately 90% in pediatric patients. However, a diagnostic accuracy of less than 50% has been reported when the Meckel scan is used in adults. Therefore, various modalities have been adopted for the diagnosis of Meckel diverticulum in adults, with the diagnostic accuracy often considered to be unsatisfactory for clinical practice. 
Plain radiography, barium studies, angiography, computed tomography (CT), and ultrasonography 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. 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. [4, 5, 6, 7]
Direct observation of the Meckel diverticulum can be done surgically, either by laparoscopy or laparotomy, or with endoscopy of the small intestine. Double-balloon endoscopy is a technique that allows the endoscope to travel further into the ileum until the Meckel diverticulum is found. Capsule endoscopy is a different technique, where a swallowed camera records the bowels while they propel it forward. A downside to capsule endoscopy is the lack of control, as it may move past the opening of the Meckel diverticulum before it is able to record it, or the camera may be facing the wrong direction when passing the mouth of the Meckel diverticulum. [8, 9]
In a study by He et al comparing the 2 advanced endoscopy techniques, double-balloon endoscopy was able to observe 64 of 74 possible Meckel diverticula. Out of 26 patients who underwent both techniques, 20 of 22 Meckel diverticula detected on double-balloon endoscopy went undetected on capsule endoscopy. The 10 diverticula that went undetected by double-balloon endoscopy were subsequently found on surgery. 
(See the images of Meckel diverticulum below.)
Meckel diverticulum occurs as a spectrum of abnormalities. In general, it is usually asymptomatic, with a 4.2–6.4% lifetime risk of complication. Meckel diverticulum manifests more commonly in children, with GI bleeding and small-bowel obstruction being the most common presentations; diverticulitis is rare.  . Complications can occur in adults, including GI bleeding, intussusception, obstruction, and diverticulitis. 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 around the Meckel diverticulum or intussusception with the diverticulum as the lead point. Meckel diverticulum is notoriously difficult to diagnose because the symptoms and imaging features are nonspecific. Imaging plays a pivotal role in the prompt recognition and differentiation from other common conditions that can have a similar clinical presentation. 
The Society of Nuclear Medicine and Molecular Imaging (SNMMI) and the European Association of Nuclear Medicine (EANM) have published joint guidelines for Meckel diverticulum scintigrapy, which include the following key recommendations  :
Plain radiographs may demonstrate appearances typical of an intestinal obstruction. [13, 14, 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. [13, 17] 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 older than 40 yr) and bowel duplications.
CT is rarely used as a primary imaging modality in patients in whom Meckel diverticulum is suspected. Most diagnoses made by using CT scans are incidental. CT has low sensitivity for the detection of uncomplicated Meckel diverticulum because its appearance mimics that of a normal bowel loop. Complicated Meckel diverticulum represents an important cause of acute abdominal pain, and most cases with inflamed Meckel diverticulum may be visualized on CT. However, diagnosis of secondary intestinal obstruction caused by Meckel diverticulum is difficult. 
Meckel diverticulum may appear as a fluid- or air-filled blind-ending pouch that arises from the antimesenteric side of the distal ileum.  It can be difficult to discern the Meckel from the adjacent loops in the small intestine, but sometimes an attached band tethering the Meckel to the umbilicus or mesentery offers additional aid in finding the right diagnosis. The amount of peritoneal fat separating the bowel loops from each other may increase the chances of detection on CT images.  Intussusception from other causes may appear similar to intussusception associated with Meckel diverticulum on CT scans. [4, 6]
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.
When observed on ultrasound, the Meckel diverticulum takes the shape of a cyst or blind pouch diverging from the ileum.  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.
Technetium-99m (99mTc) pertechnetate scintigraphy, commonly known as the Meckel scan, is considered to be the modality of choice to evaluate patients with suspected Meckel diverticulum, based on its diagnostic accuracy of approximately 90% in pediatric patients. However, a diagnostic accuracy of less than 50% has been reported when the Meckel scan is used in adults. Therefore, various modalities have been adopted for the diagnosis of Meckel diverticulum in adults, with the diagnostic accuracy often considered to be unsatisfactory for clinical practice.  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 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, 7]
(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 before the procedure. The quality of images is poor in patients who have received perchlorate or atropine.
The administration of certain drugs before 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.
A false-negative result may occur if the patient underwent prior barium fluoroscopy examination or prior administration of perchlorate, and a false-positive result may occur if there was a prior cleansing enema or laxatives that caused bowel irritation. 
A false-positive result may occur if there is focal pooling of tracer in the urinary tract (hydronephrosis, extrarenal pelvis, ectopic kidney, hydroureter, vesicourethral reflux, bladder diverticulum) or if there is a uterine blush. False-positive radiopharmaceutical activity suggestive of Meckel diverticula can result from the following conditions: duplication cyst with ectopic gastric mucosa, bowel inflammation, intussusception or small-bowel obstruction, peptic ulcer, and vascular lesions with increased blood pool (eg, hemangioma or arteriovenous malformation). 
A false-negative result may occur if the image is obscured by brisk gastrointestinal bleeding during circulation of the tracer or by the urinary bladder or dilated ureter, if a focus of ectopic mucosa is small (< 1.8 cm2), and if there is movement of the diverticulum. Other pathologic conditions that may result in a false-negative scan include gastrointestinal bleeding unrelated to ectopic gastric mucosa (eg, pancreatic mucosa). A negative Meckel scan in a patient with significant recent gastrointestinal bleeding where no other etiology for bleeding is discovered over several weeks’ time may warrant a repeated study, optimally using pretreatment with an H2-receptor blocker or proton pump inhibitor. 
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. The vitelline artery is an elongated vessel with few or no branches, which usually arises from a distal ileal branch of the superior mesenteric artery. Visualization of this artery on arteriography is diagnostic for Meckel diverticulum. 
It is also characteristic to see a group of dilated tortuous vessels at the distal portion of the vitelline artery without branches. Superselective vitelline arteriography facilitates the visualization of these distal-most findings. Other angiographic evidence for Meckel diverticulum includes a vascular blush (which may relate to the presence of ectopic gastric mucosa) or active hemorrhage, as evidenced by extravasation of contrast into the bowel lumen. Angiography can detect a Meckel diverticulum even in the absence of acute bleeding via visualization of the vitelline artery. 
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Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR Consultant Radiologist and Honorary Professor, North Manchester General Hospital Pennine Acute NHS Trust, UK
Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR is a member of the following medical societies: American Association for the Advancement of Science, American Institute of Ultrasound in Medicine, British Medical Association, Royal College of Physicians and Surgeons of the United States, British Society of Interventional Radiology, Royal College of Physicians, Royal College of Radiologists, Royal College of Surgeons of England
Disclosure: Nothing to disclose.
Muthusamy Chandramohan, MBBS, DMRD, FRCR Consultant Radiologist, Bradford Teaching Hospitals, UK
Disclosure: Nothing to disclose.
Sumaira Macdonald, MBChB, PhD, FRCP, FRCR, EBIR Chief Medical Officer, Silk Road Medical
Sumaira Macdonald, MBChB, PhD, FRCP, FRCR, EBIR is a member of the following medical societies: British Medical Association, Cardiovascular and Interventional Radiological Society of Europe, British Society of Interventional Radiology, International Society for Vascular Surgery, Royal College of Physicians, Royal College of Radiologists, British Society of Endovascular Therapy, Scottish Radiological Society, Vascular Society of Great Britain and Ireland
Disclosure: Received salary from Silk Road Medical for employment.
Bernard D Coombs, MB, ChB, PhD Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand
Disclosure: Nothing to disclose.
David A Stringer, MBBS, FRCR, FRCPC Professor, National University of Singapore; Head, Diagnostic Imaging, KK Women’s and Children’s Hospital, Singapore
David A Stringer, MBBS, FRCR, FRCPC is a member of the following medical societies: Royal College of Physicians and Surgeons of Canada, Royal College of Radiologists, Society for Pediatric Radiology, British Columbia Medical Association, European Society of Paediatric Radiology
Disclosure: Nothing to disclose.
John Karani, MBBS, FRCR Clinical Director of Radiology and Consultant Radiologist, Department of Radiology, King’s College Hospital, UK
John Karani, MBBS, FRCR is a member of the following medical societies: British Institute of Radiology, Radiological Society of North America, Royal College of Radiologists, Cardiovascular and Interventional Radiological Society of Europe, European Society of Radiology, European Society of Gastrointestinal and Abdominal Radiology, British Society of Interventional Radiology
Disclosure: Nothing to disclose.
Meckel Diverticulum Imaging
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