I-131 MIBG Scan

I-131 MIBG Scan (Metaiodobenzylguanidine Scan)

An I-131 MIBG scan is a nuclear medicine imaging test used to detect and evaluate tumors that arise from the adrenal glands and nervous system, particularly pheochromocytomas and neuroblastomas. The scan utilizes Iodine-131 labeled metaiodobenzylguanidine (MIBG), which is selectively taken up by adrenergic tissue.

Indications for I-131 MIBG Scan:

• Pheochromocytoma (tumors of the adrenal medulla producing catecholamines).

• Paragangliomas (extra-adrenal pheochromocytomas).

• Neuroblastoma (common pediatric cancer of the nervous system).

• Medullary Thyroid Cancer (MTC) (in some cases).

• Carcinoid Tumors and other neuroendocrine tumors.

Procedure:

1. Preparation:

   • Thyroid blocking with potassium iodide (Lugol’s solution) is required to prevent unnecessary thyroid uptake of radioactive iodine.

   • Certain medications (e.g., calcium channel blockers, labetalol, reserpine) may need to be discontinued.

2. Injection:

   • A small dose of I-131 MIBG is administered intravenously.

3. Imaging:

   • First scan: Performed 24 hours after injection.

   • Delayed scans: May be done at 48 and 72 hours to improve sensitivity.

   • SPECT/CT may be used to enhance localization.

Results Interpretation:

• Positive scan: Areas of increased MIBG uptake indicate the presence of neuroendocrine tumors.

• Negative scan: No abnormal uptake, suggesting the absence of MIBG-avid disease.

• False negatives: Some tumors may not take up MIBG, requiring alternative imaging (e.g., PET scan with Ga-68 DOTATATE).

Advantages of I-131 MIBG Scan:

✅ High specificity for adrenergic tissue tumors.
✅ Useful for staging and detecting metastases.
✅ Can be used therapeutically (high-dose I-131 MIBG therapy) for metastatic neuroblastoma or pheochromocytoma.