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Adrenal scintigraphy, MIBG and phaeochromocytoma
Functional adrenal imaging imitates the tissue's biological pathway — MIBG is taken up like noradrenaline in chromaffin cells, F-DOPA enters the catecholamine synthesis pathway, Ga-68 DOTATATE binds somatostatin receptors, and NP-59 is taken up like cholesterol in the adrenal cortex.
Why it matters in the exam
The exam asks which study is best for finding phaeochromocytoma outside the adrenal (paraganglioma) and metastases, which drug interferes with MIBG, and what NP-59 shows. The joint EANM and SNMMI guidance advises choosing by location and genetics: Ga-68 DOTATATE PET is the most sensitive study in head-and-neck paragangliomas, metastatic disease and SDHx mutations; F-DOPA PET is excellent for adrenal phaeochromocytoma and mutations such as VHL and RET; FDG is particularly sensitive in SDHB mutations. I-123 MIBG remains important mainly to test suitability for I-131 MIBG therapy.
Preparation for MIBG: thyroid blockade with stable iodine (Lugol solution or potassium iodide) to prevent uptake of free iodine, and stopping drugs that interfere with uptake through the noradrenaline transporter or with granule storage — labetalol, tricyclic antidepressants, sympathomimetics, reserpine and some calcium channel blocker preparations. Ordinary beta-blockers interfere less. Normal uptake is seen in the liver, salivary glands, heart and urine, and only faintly in the normal adrenal.
NP-59 (iodomethyl-norcholesterol) is imaged several days after injection, sometimes with dexamethasone suppression; early unilateral uptake points to an aldosterone- or cortisol-secreting adenoma, and bilateral uptake to hyperplasia. Today it is rare and adrenal vein sampling is used instead. In childhood neuroblastoma MIBG is the basis for staging and follow-up, with uptake in more than 90% of tumours. The diagnosis of phaeochromocytoma always starts with plasma or urine metanephrines; imaging comes after biochemical confirmation.
Key points
- Functional imaging imitates a biological pathway.
- Ga-68 DOTATATE — first choice in metastatic and head-and-neck disease.
- I-123 MIBG — for therapy suitability and neuroblastoma.
- Before MIBG: thyroid blockade and stop labetalol and tricyclics.
- Diagnosis starts with metanephrines.
Summary table
| Agent | Principle | When preferred | Note |
|---|---|---|---|
| I-123 MIBG | Noradrenaline transporter | Suitability for I-131 MIBG therapy, neuroblastoma | Block the thyroid; stop labetalol and tricyclics |
| F-18 DOPA PET | Catecholamine synthesis pathway | Adrenal phaeochromocytoma, VHL, RET | Very sensitive |
| Ga-68 DOTATATE PET | Somatostatin receptors | Head and neck, metastases, SDHx | First choice in metastatic disease |
| FDG PET | Glycolysis | SDHB, aggressive disease | Less specific |
| NP-59 | Cortical cholesterol uptake | Secreting adenoma versus hyperplasia | Rare; vein sampling instead |
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Sources
- EANM/SNMMI Practice Guideline for Radionuclide Imaging of Phaeochromocytoma and Paraganglioma, 2019 — Choice of radiopharmaceutical by genotype and location
- Endocrine Society Clinical Practice Guideline: Pheochromocytoma and Paraganglioma, 2014 — Functional imaging
- EANM Procedure Guidelines for I-123 MIBG Scintigraphy, 2010 — Patient preparation and interfering drugs
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.