Phaeochromocytoma - Paraganglioma
Pearls
On imaging: T2 very bright (“light-bulb”), avid enhancement, may be cystic/haemorrhagic. Never biopsy until biochemistry excludes a phaeo. Pre-op: α-blockade first, volume expansion; add β-blocker only after α-blockade.
- Adrenal (phaeo) – usually functional.
- Extra-adrenal sympathetic PG – often functional.
- Extra-adrenal parasympathetic (H&N) PG – usually non-functional, also often less dramatic T2 light-bulb sign.
- Old ‘rule of 10s’ (≈10% bilateral, ≈10% extra-adrenal, ≈10% malignant, ≈10% in children) is outdated but still pops up in exams – now we know ~30–40%+ hereditary.”
Clinical significance
- Crisis risk with procedures/anaesthesia; potentially curable cause of hypertension.
- A substantial fraction are hereditary (e.g., RET/MEN2, VHL, NF1, SDHx); genetics affects surveillance and family screening
- Histology cannot reliably distinguish benign vs malignant; malignancy defined by metastases (nodes, bone, lung, liver).
Risk higher in: extra-adrenal, large size, SDHB mutation.
Imaging pearls
CT
- Solid, usually >10 HU in non-contrast phase, strongly enhancing mass; may be heterogeneous with haemorrhage/cystic change.
- Non-diagnostic to rely on washout CT; phaeos can show brisk “washout” → do not use washout to exclude phaeo.
MRI
- T2 very hyperintense ("light-bulb sign")
- More typical of larger adrenal / sympathetic lesions.
- Small or fibrotic tumours may be only mildly T2 bright.
- T1 variable (blood products ↑T1).
- Avid enhancement; restricted diffusion on DWI (diffusion-weighted imaging) is common.
- Chemical-shift imaging (CSI): typically no signal drop (distinguishes from intracellular-lipid adenoma). Rare lipid-containing phaeos exist → correlate with labs.
Nuclear medicine
- MIBG scintigraphy/SPECT: catecholamine-specific.
Classically for adrenal phaeo and some sympathetic PG; less sensitive in SDHB / aggressive disease. - FDG PET: especially good for SDHB-mutant / metastatic PPGL.
- DOTATATE PET: great for paragangliomas and for planning PRRT.
Differential diagnosis
- Adrenal adenoma
- CSI signal drop OR
- Unenhanced HU ≤10
- Adrenocortical carcinoma
- Giant, irregular, invasive, necrotic; variable enhancement
- Especially if hormone excess is cortisol/androgen rather than catecholamine phenotype.
- Metastasis
- Oncology history
- Variable appearance, often less T2 bright
- Myelolipoma with haemorrhage
- Macroscopic fat foci
- Adrenal cyst/pseudocyst
- No internal enhancement; T2 bright, T1 dark unless blood).
Management pearls
First-line workup
- Plasma free or urinary fractionated metanephrines (most sensitive screening).
- Borderline results → consider clonidine suppression test (per endocrine protocol).
Safety & biopsy
Do not biopsy an adrenal mass until phaeochromocytoma is excluded
Needle manipulation can trigger catecholamine crisis (hypertensive emergency, arrhythmia, pulmonary oedema, intracranial haemorrhage). If tissue is essential (e.g., staging with known cancer), do biochemical testing first and proceed only after α-blockade with full monitoring.
Pre-operative optimisation
- α-blockade before any β-blocker typically for 7–14 days pre-op.
- Liberal salt and fluid intake to restore intravascular volume.
- Add short-acting β-blocker after adequate α-blockade for tachyarrhythmia.
- Anaesthesia: arterial line, vasodilators and magnesium available.
Post-op / follow-up
- Monitor for hypotension and hypoglycaemia immediately post-resection.
- Repeat metanephrines for biochemical cure; interval imaging if hereditary or metastatic risk.
Genetics workup
High hereditary yield; consider genetic counselling/testing (e.g., RET, VHL, NF1, SDHB/SDHD), especially if young, bilateral, extra-adrenal, multifocal, or metastatic.
- SDHB → higher metastatic risk, often extra-adrenal trunk disease → favour FDG/DOTATATE over MIBG.
- SDHD / SDHAF2 → multiple head & neck PG
Potential pitfalls
- Cystic phaeos can mimic a “simple cyst”—look for enhancing mural nodules/septa.
- Brisk washout does not rule out phaeo.
- Rare lipid-containing phaeos can show partial CSI drop—labs decide.
- Small extra-adrenal paragangliomas along sympathetic chain can be missed without careful search or functional imaging.
- Head & neck paragangliomas are often non-functional – normal catecholamines do not exclude PG here. Use somatostatin-receptor imaging if multifocal disease suspected.
