What is a Meckel's scan (Technetium-99m pertechnetate scan)?

From the Guidelines

A Meckel's scan is a nuclear medicine imaging test that involves the intravenous administration of 99mTc pertechnetate to detect a Meckel's diverticulum, a congenital pouch on the small intestine that contains gastric mucosa. The scan is used to investigate for a Meckel diverticulum, particularly in children and young adults with unexplained gastrointestinal bleeding 1. The technique involves scintigraphy performed dynamically for a period of 30–60 minutes to identify a fixed abdominal region of ectopic gastric mucosa.

Key Points

• The scan is particularly useful in children with unexplained gastrointestinal bleeding, as Meckel's diverticulum is a common cause of significant lower GI bleeding in this population.
• A Meckel scan can be considered to identify the cause of unexplained intermittent GI bleeding in children and adolescents after negative endoscopic evaluation, including capsule endoscopy if available, and cross-sectional evaluation of the small bowel 1.
• The scan has a high sensitivity and specificity for detecting Meckel's diverticulum containing gastric mucosa, making it a valuable diagnostic tool in clinical practice.

Clinical Considerations

• Patients typically fast for 4-6 hours before the test, and medications that might interfere with the scan should be discontinued 48-72 hours prior.
• Some centers administer pentagastrin or cimetidine before the scan to enhance sensitivity.
• Images are taken immediately after injection and continue for about 30-60 minutes.
• The test is useful in identifying Meckel's diverticulum, which can help guide treatment and management of gastrointestinal bleeding.

From the FDA Drug Label

INDICATIONS AND USAGE: The Technelite generator is a source of sodium pertechnetate Tc 99m for use in the preparation of FDA-approved diagnostic radiopharmaceuticals, as described in the labeling of these diagnostic radiopharmaceutical kits. Sodium Pertechnetate Tc 99m Injection is used IN ADULTS as an agent for: Thyroid Imaging Salivary Gland Imaging Urinary Bladder Imaging (direct isotopic cystography) for the detection of vesico-ureteral reflux. Nasolacrimal Drainage System Imaging Sodium Pertechnetate Tc 99m Injection is used IN CHILDREN as an agent for: Thyroid Imaging Urinary Bladder Imaging (direct isotopic cystography) for the detection of vesico-ureteral reflux.

The FDA drug label does not answer the question.

From the Research

Definition and Purpose of Meckel's Scan

• A Meckel's scan, also known as a Technetium-99m pertechnetate scan, is a diagnostic imaging test used to detect Meckel's diverticulum, a congenital abnormality of the gastrointestinal tract 2, 3, 4, 5, 6.
• The scan involves the use of a small amount of radioactive material, Technetium-99m pertechnetate, which accumulates in the mucous cells of ectopic gastric mucosa, allowing for the detection of Meckel's diverticulum 2, 3, 4, 5, 6.

Sensitivity and Specificity of Meckel's Scan

• The Meckel's scan has a high sensitivity and specificity for detecting Meckel's diverticulum, with a positive predictive value of 0.93 and a negative predictive value of 0.74 in patients with lower GI bleeding and a hemoglobin level less than 11.0 g/dL 4.
• The scan has a true positive rate of 84.2% for detecting gastric mucosa in pediatric patients with Meckel's diverticulum 5.

Clinical Applications of Meckel's Scan

• The Meckel's scan is commonly used to evaluate children with unexplained gastrointestinal tract bleeding, particularly in cases where other imaging modalities such as endoscopy and ultrasound are normal 2, 3, 6.
• The scan can help identify the presence of a Meckel's diverticulum and guide surgical intervention to achieve the best possible outcome for the patient 6.

Limitations and Challenges of Meckel's Scan

• The Meckel's scan may have a relatively low negative predictive value, which can result in the need for operative evaluation despite the scan data 4.
• False-negative scans can occur, and clinical suspicion may play a major role in the decision-making process, leading to exploratory laparoscopy or laparotomy despite the scan results 4.