What is the purpose and procedure of a Meckel (Meckel's diverticulum) scan?

Meckel's Diverticulum Scan: Purpose and Procedure

A Meckel scan is a nuclear medicine imaging test used to detect Meckel's diverticulum containing ectopic gastric mucosa, primarily in patients with unexplained gastrointestinal bleeding, particularly in children and young adults. 1

Purpose of the Meckel Scan

The primary purposes of a Meckel scan include:

• Identifying Meckel's diverticulum containing ectopic gastric mucosa
• Diagnosing the source of unexplained gastrointestinal bleeding
• Localizing ectopic gastric tissue in the abdomen
• Providing a non-invasive diagnostic option before considering surgery

Meckel's diverticulum is a congenital anomaly that represents a remnant of the omphalomesenteric duct. When it contains ectopic gastric mucosa (which occurs in approximately 50% of cases), it can secrete acid and cause ulceration and bleeding.

Patient Selection

Meckel scans are most appropriate for:

• Children and young adults with unexplained gastrointestinal bleeding
• Patients with occult GI bleeding after negative upper and lower endoscopy
• Cases where other tests are negative but clinical suspicion remains high

While most symptomatic Meckel's diverticula are found in children and young adults, they can occasionally be seen in older individuals and should be considered when other diagnostic tests are negative 1.

Procedure Details

The Meckel scan procedure involves:

1. Radiopharmaceutical Administration: Intravenous injection of technetium-99m pertechnetate, which is selectively taken up by gastric mucosa, including ectopic gastric tissue in a Meckel's diverticulum 1, 2

2. Imaging Protocol:

   • Dynamic scintigraphy performed for 30-60 minutes after injection
   • Images acquired to identify a fixed abdominal region of ectopic gastric mucosa
   • Patient positioned supine during imaging 1

3. Dose:

   • Adult dose: Typically 370-555 MBq (10-15 mCi) of technetium-99m pertechnetate
   • Pediatric dose: 2.22-2.96 MBq (60-80 μCi) per kg of body weight 2

4. Duration: The entire procedure typically takes 60-90 minutes, including preparation and imaging time

Diagnostic Accuracy and Limitations

The diagnostic accuracy of Meckel scans varies by age group:

• Pediatric patients: Approximately 90% accuracy
• Adult patients: Lower accuracy with more frequent false-positive and false-negative results 3

Limitations:

• False-negative results can occur despite the presence of ectopic gastric mucosa
• False-positive results are relatively common in adults
• Limited sensitivity for Meckel's diverticula without gastric mucosa
• Decreased accuracy in patients with active bleeding that may wash out the radiotracer

Advanced Techniques

To improve diagnostic accuracy, newer techniques include:

• SPECT/CT fusion imaging: Combines functional and anatomical information, providing better localization and preventing false-negative studies 4
• Pharmacologic augmentation: Use of medications like H2 blockers or proton pump inhibitors prior to scanning to increase tracer uptake

Alternative Diagnostic Methods

When Meckel scan results are equivocal or negative despite high clinical suspicion:

• Double-balloon enteroscopy (DBE) has shown superior diagnostic yield (86.5%) compared to capsule endoscopy (7.7%) for detecting Meckel's diverticulum 5
• CT enterography may help identify small bowel masses and other potential bleeding sources
• Small bowel infusion studies or mesenteric angiography may be considered as supplementary tests 3

Clinical Considerations

• The scan is most valuable in children and young adults with unexplained GI bleeding
• In adults with recurrent, unexplained lower GI bleeding, supplementary diagnostic methods should be considered alongside the Meckel scan
• Surgical exploration may still be necessary in cases with high clinical suspicion despite negative imaging

By providing a non-invasive means to detect ectopic gastric mucosa, the Meckel scan plays an important role in diagnosing this uncommon but clinically significant cause of gastrointestinal bleeding.