Quick summary
Tc-99m pertechnetate concentrates in gastric mucosa parietal cells and is used to detect ectopic gastric mucosa within a Meckel's diverticulum. The scan only detects Meckel's diverticula containing ectopic gastric mucosa — present in ~25–50% of all Meckel's, but ~80–90% of symptomatic/bleeding Meckel's. Classic presentation: painless rectal bleeding in a child.
Radiopharmaceutical: Tc-99m pertechnetate, 5–10 mCi (weight-based in pediatric patients).
Findings and Interpretation
| Finding |
Interpretation |
| Focal ectopic activity appearing simultaneously with gastric mucosa, in RLQ or ectopic location, increasing in intensity over time |
Meckel's diverticulum with ectopic gastric mucosa — positive scan (sensitivity ~85–90% in children) |
| Activity appearing after gastric uptake, or not increasing in intensity |
Normal variant (blood pool, ureteral activity) or negative scan — Meckel's not excluded if no ectopic gastric mucosa present |
A negative scan does not exclude Meckel's diverticulum. ~50% of asymptomatic Meckel's lack ectopic gastric mucosa. With high clinical suspicion, surgical exploration remains appropriate even after a negative scan.
Pretreatment to Improve Sensitivity
| Agent |
Dose |
Mechanism |
| Cimetidine (most commonly used) |
300 mg PO q6h × 2 days before scan |
Blocks Tc-99m washout from gastric mucosa; increases sensitivity to ~95% |
| Pentagastrin |
6 µg/kg SQ × 15 min before scan |
Stimulates gastric mucosa uptake; avoid in active GI bleed |
| Glucagon |
50 µg/kg IV |
Reduces bowel motility, decreases redistribution of activity |
Pitfalls
| Pitfall |
Explanation |
| Ureteral activity |
Right ureter can mimic RLQ ectopic uptake; always void before scanning; obtain lateral views; activity clears with voiding |
| Intussusception |
Can trap pertechnetate → false positive; correlate with ultrasound |
| No ectopic gastric mucosa |
Negative scan does not exclude Meckel's; surgical exploration may still be warranted with high clinical suspicion |
| IBD / duplication cyst |
Both can contain ectopic gastric mucosa → false positive; clinical and ultrasound correlation required |
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