Pheochromocytoma: Basic to Clinical

1. Definition and Etymology

• Incidence: 2-8 cases per million per year; found in ~0.2-0.6% of hypertensive patients
• Peak age (sporadic): 40-50 years; familial cases manifest earlier
• Males and females affected equally

"Pheochromocytoma has been described as a biologic time bomb because of the potentially lethal cardiovascular effects of the bioactive compounds secreted by these tumors." - Sabiston Textbook of Surgery

2. The "10% Rule" - Historical and Modern Revisions

3. Embryology and Cell of Origin

• The adrenal medulla (most common site - ~80-85% of PPGLs)
• Extra-adrenal sympathetic ganglia chain along the aorta
• The organ of Zuckerkandl - the largest collection of extra-adrenal chromaffin tissue, located at the bifurcation of the aorta or the origin of the inferior mesenteric artery (most common site for extra-adrenal paraganglioma)
• Carotid body, jugular-tympanic region, urinary bladder

4. Genetics and Molecular Pathogenesis

Cluster 1 - Pseudohypoxia Pathway (HIF activation)

Cluster 2 - Kinase Signaling / RAS-MAPK-PI3K

• RET, NF1: enhance growth factor receptor/RAS signaling
• VHL, SDHx, EPAS1: increase HIF activity → pseudohypoxic response → tumor growth
• All pathways ultimately drive uncontrolled chromaffin cell proliferation

Genetic testing is indicated in: bilateral/multiple tumors, extra-adrenal location, age <40 years, family history, or malignant disease. Cascade testing for SDHx, VHL, and RET should be pursued.

5. Pathology

Gross Morphology

• Range from small circumscribed nodules to large hemorrhagic masses weighing several kilograms
• Cut surface: yellow-tan (small tumors) to hemorrhagic, necrotic, cystic (large tumors)
• Fresh tissue + potassium dichromate → dark brown (positive chromaffin reaction)

Pheochromocytoma: (A) Hemorrhagic tumor enclosed within attenuated cortex. (B) Characteristic nests of chromaffin cells with abundant cytoplasm and rich vascular network.

Microscopic Features

• Polygonal to spindle-shaped chromaffin cells with supporting (sustentacular) cells
• Arranged in characteristic "Zellballen" (cell balls) - small nests compartmentalized by a rich vascular network
• Finely granular cytoplasm containing catecholamine-laden granules (highlighted by silver stains; electron-dense on EM)
• Nuclei often pleomorphic - this does NOT indicate malignancy
• Capsular and vascular invasion may be present in benign lesions

Photomicrograph showing characteristic nests of cells with abundant cytoplasm. Bizarre/pleomorphic cells (such as the large cell in center) can appear even in benign tumors.

Defining Malignancy

6. Catecholamine Biochemistry

Tyrosine → DOPA → Dopamine → Norepinephrine → Epinephrine
                                   ↓              ↓
                           Normetanephrine    Metanephrine
                                   ↓              ↓
                           Vanillylmandelic acid (VMA)

• Rate-limiting step: Tyrosine hydroxylase (converts tyrosine → DOPA)
• Catecholamines are stored in chromaffin granules and released by exocytosis
• Metanephrines (normetanephrine, metanephrine) are formed by continuous O-methylation within the tumor cells even between episodes - this is why they are more sensitive markers than catecholamines themselves
• Final common metabolite: VMA (vanillylmandelic acid), excreted in urine

7. Clinical Features

The Classic Triad (present in ~95% in large series)

1. Episodic headache (severe, pounding)
2. Diaphoresis (generalized sweating)
3. Palpitations / tachycardia

Hypertension Patterns

• Sustained hypertension: most common (~50%)
• Paroxysmal hypertension (episodic "spells"): ~2/3 of patients also have paroxysmal episodes superimposed on chronic hypertension
• ~10% are normotensive (incidentally discovered "silent pheos")

Paroxysmal Episodes ("Spells")

• Abrupt BP elevation
• Headache, sweating, palpitations
• Tremor, anxiety, sense of doom
• Abdominal/chest pain, nausea, vomiting
• Duration: minutes to hours

Life-threatening Presentations

• Hypertensive crisis → stroke, ICH
• Acute MI, ventricular fibrillation
• Catecholamine-induced cardiomyopathy (dilated or Takotsubo-like)
• Pulmonary edema
• Pheochromocytoma crisis: multiorgan failure with fever, encephalopathy, shock

Special Presentations

• Micturition syncope/headache: bladder paraganglioma
• Cushing features: ACTH-secreting tumor
• Hypoglycemia: insulin or IGF-secreting component
• Heart failure as presenting complaint (catecholamine cardiomyopathy)
• Incidental adrenal mass on imaging ("incidentaloma")

Physical Exam Clues to Familial Syndromes

8. Biochemical Diagnosis

First-Line Tests (either or both recommended)

"Plasma free metanephrine testing carries an extremely high sensitivity, approaching 99%... the primary usefulness of plasma free metanephrine testing is to exclude pheochromocytoma when the test result is negative." - Sabiston Textbook of Surgery

• Plasma/urine free metanephrine concentrations above 2x the upper limit of normal are diagnostic and essentially confirmatory.
• For borderline results: clonidine suppression test (clonidine 0.3 mg PO → normetanephrine suppresses in essential hypertension but NOT in PPGL)

Second-Line / Supplementary Tests

• 24h urine catecholamines (norepinephrine, epinephrine, dopamine)
• 24h urine VMA (less sensitive than metanephrines)
• Urine dopamine elevated in SDHB-related or dopamine-secreting tumors

Interfering Substances (cause false positives)

• Tricyclic antidepressants, SNRIs
• Labetalol (interferes with HPLC-based assays)
• Levodopa
• Acetaminophen (some assays)
• Physical stress, catecholamine infusions

9. Imaging and Localization

Anatomic Imaging

• Sensitivity: 90-100% for adrenal PPGL
• HU >10 on unenhanced CT (pheos are lipid-poor; adenomas typically <10 HU)
• Vigorous early enhancement with <60% venous phase washout
• Typical HU 40-50 on non-contrast CT
• CT neck/chest/abdomen/pelvis (with and without contrast) for complete survey

• Preferred in: pregnant or lactating patients, pediatric patients, CT contrast allergy, desire to avoid radiation
• Classic: very bright on T2-weighted sequences ("light bulb sign") due to high vascularity and water content - but not always present
• No chemical shift dropout (unlike adrenal adenoma)
• Higher sensitivity for extra-adrenal PGL than CT

MRI of right adrenal pheochromocytoma. Note no signal dropout on OOP sequence (no lipid content), with T2 hyperintensity - characteristic features distinguishing it from adrenal adenoma.

Functional Imaging (when anatomic imaging inconclusive, or for metastatic workup)

10. Preoperative Management

Step 1: Alpha-Adrenergic Blockade (MANDATORY - start FIRST)

• Non-selective, non-competitive, irreversible alpha-blocker
• Start 10 mg BID, titrate every 2-3 days up to 40 mg TID
• Long half-life (24h) allows decay in parallel with catecholamines postoperatively
• Side effects: postural hypotension, nasal congestion, reflex tachycardia
• Duration: at least 10-14 days preoperatively

• Increasingly preferred due to cost/availability issues with phenoxybenzamine
• Selective alpha-1 blockade; less reflex tachycardia
• More intraoperative hemodynamic fluctuation; requires excellent anesthesia-surgery communication

Step 2: Beta-Blockade (ONLY AFTER alpha-blockade established)

• For persistent tachycardia (often in epinephrine-predominant tumors)
• NEVER give beta-blocker first - unopposed alpha-adrenergic tone will worsen hypertension and may precipitate crisis

Volume Expansion

• Alpha-blockade creates venous capacitance increase - encourage high-salt diet and oral fluid intake
• IV fluids preoperatively if significant orthostasis

Goals of Preoperative Optimization

• BP <130/80 mmHg seated, no orthostatic drop >10 mmHg
• HR 60-70 bpm seated; no more than 80 standing
• No ST/T wave changes on ECG
• Nasal stuffiness = sign of adequate alpha-blockade

11. Surgical Management

Approach

• Laparoscopic adrenalectomy is now the standard of care for most adrenal pheochromocytomas (tumors <6 cm, no local invasion)
• Open adrenalectomy for large (>6 cm), invasive, or malignant-appearing tumors, or those requiring en-bloc resection
• Cortical-sparing adrenalectomy is recommended for bilateral tumors (to preserve adrenocortical function) - supported by recent meta-analysis [PMID 40214691, 2025]
• For extra-adrenal PGL: laparoscopic or open resection depending on location

Intraoperative Considerations

• Arterial line, large-bore IV access, central line
• Minimize tumor manipulation
• Intraoperative hypertension: IV phentolamine (non-selective alpha), sodium nitroprusside, or nicardipine
• Intraoperative tachyarrhythmias: esmolol, lidocaine
• Post-ligation hypotension (after adrenal vein ligation): sudden withdrawal of catecholamines → vasodilation + increased venous capacitance → cardiovascular collapse. Manage with aggressive IV fluids and vasopressors (vasopressin often more effective due to preoperative alpha-blockade)

Postoperative Care

• Hypoglycemia monitoring (catecholamine-mediated gluconeogenesis/glycogenolysis resolves)
• Hypotension: treat with IV fluids, vasopressors
• Watch for adrenal insufficiency after bilateral adrenalectomy

12. Malignant Pheochromocytoma

• Diagnosed only by presence of metastases - not histology
• Metastatic sites: liver, bone, lung, lymph nodes
• SDHB mutation = strongest predictor of malignant behavior (up to 50% metastatic rate)
• 5-year survival for metastatic PPGL: ~35-60%

Treatment of Metastatic Disease

13. Special Populations

Pheochromocytoma in Pregnancy

• Rare but potentially fatal - 12% fetal mortality if diagnosed antenatally
• Unrecognized PPGL in pregnancy: 27x increase in maternal and fetal complications
• Management: alpha-blockade is the cornerstone
• If diagnosed <24 weeks: laparoscopic adrenalectomy in 2nd trimester is an option
• If diagnosed in 3rd trimester: alpha-blockade until cesarean delivery, then tumor resection

Pediatric PPGL

• 70-80% are hereditary (vs ~40% in adults)
• Higher rate of bilateral, multifocal, extra-adrenal, and metastatic disease
• Genetic testing is essentially universal

14. Familial Syndromes Summary

15. Postoperative Follow-up

• Biochemical testing (plasma free metanephrines or 24h urine) at 2-6 weeks post-op to confirm biochemical cure
• Annual biochemical surveillance for life (recurrence risk ~17%)
• Imaging if biochemistry becomes elevated again
• Genetic counseling and cascade family screening for all mutation carriers

Key Clinical Pearls

1. Never give beta-blockers alone to a hypertensive patient with suspected pheo - it will worsen the crisis by unopposed alpha-stimulation.
2. Plasma free metanephrines are the most sensitive test (99%) - a negative result essentially rules out pheo.
3. SDHB mutation = think malignancy, pursue whole-body functional imaging.
4. The chromaffin reaction (dichromate turns tissue brown) = the basis of the tumor's name.
5. Histologic pleomorphism and capsular invasion do not define malignancy - only metastasis does.
6. "Silent pheos" (normotensive, incidentally found) are increasing in frequency as cross-sectional imaging becomes more widespread.
7. Postoperative hypoglycemia and hypotension are expected consequences of sudden catecholamine withdrawal.
8. In bilateral disease, cortical-sparing adrenalectomy is preferred to avoid lifelong steroid replacement.
9. Bladder paraganglioma classically presents with micturition-induced hypertensive spells or syncope.
10. Any adrenal incidentaloma workup must include pheochromocytoma screening before biopsy or surgery to prevent triggering a crisis.

• Robbins & Kumar Basic Pathology (9780323790185), pp. 761-763
• Sabiston Textbook of Surgery (9780443124341), Adrenal Surgery chapter
• Current Surgical Therapy 14e (9780323796835), pp. 869-872
• Brenner and Rector's The Kidney, 2-vol (9780323532655), pp. relevant sections
• Campbell-Walsh-Wein Urology (9780323546423), Chapter 106

• A 2025 meta-analysis [PMID 40214691] on partial adrenalectomy for pheochromocytoma confirms cortical-sparing surgery has comparable oncological outcomes to total adrenalectomy with preserved adrenal function - supporting its use in bilateral disease.
• Japan Endocrine Society [PMID 41083371] published updated 2025 guidelines on PPGL diagnosis and management, incorporating ⁶⁸Ga-DOTATATE PET as a major imaging advance and updating genetic testing recommendations.

Investigations of Pheochromocytoma

Critical Rule: Biochemical diagnosis MUST precede imaging. Never proceed to biopsy of any adrenal mass before excluding pheochromocytoma - catecholamine release during needle biopsy can precipitate a fatal hypertensive crisis.

Phase 1 - Biochemical Diagnosis

Why Metanephrines, Not Catecholamines?

• Norepinephrine → Normetanephrine (via COMT)
• Epinephrine → Metanephrine (via COMT)
• Both → VMA (vanillylmandelic acid) after further MAO metabolism
• The term "free" = unconjugated (not sulfonated); "fractionated" = individual subtype measurements (normetanephrine and metanephrine separately, not as a combined total)

Test 1: Plasma Free Metanephrines (First-Line)

• Collect supine after 30 minutes of rest (standing increases normetanephrine by ~2x physiologically)
• Discontinue interfering medications if possible before testing
• A negative result effectively excludes pheochromocytoma - the primary value of this test is its negative predictive power
• False positive rate is high: in a tertiary hypertension clinic, an estimated 97% of patients with abnormal plasma metanephrines do NOT have pheochromocytoma - because the disease is rare (~0.2% of hypertensives)
• False positives outnumber true positives by as much as 30:1 when used as a population screening tool

Test 2: 24-Hour Urine Fractionated Metanephrines + Catecholamines (First-Line / Confirmatory)

Normetanephrine 8760 µg/24h (normal <900 µg), norepinephrine 781 µg/24h (normal <170 µg) - 5-cm right adrenal pheochromocytoma confirmed on CT

Test 3: VMA (Vanillylmandelic Acid) - Urine

• End metabolite of catecholamine degradation (via both MAO and COMT)
• Long used historically but now least sensitive of the catecholamine tests (sensitivity only 46-77%)
• High specificity (86-99%), especially useful when positive
• No longer recommended as a first-line test; largely replaced by metanephrine assays

Test 4: Clonidine Suppression Test (Adjunctive/Confirmatory)

• Patient supine; baseline plasma normetanephrine measured
• Oral clonidine 0.3 mg administered
• Repeat plasma normetanephrine at 3 hours

• Normal response (excludes pheo): Normetanephrine falls to <0.61 nmol/L (suppressed)
• Positive (supports pheo): Normetanephrine remains elevated (NOT suppressed) despite clonidine
• A normal clonidine suppression test also defined by total catecholamines falling to <500 pg/mL within 2-3 hours

Test 5: Chromogranin A (Supplementary)

• Acidic monomeric protein co-stored in chromaffin granules and released alongside catecholamines
• Sensitivity ~83%, specificity ~96%
• Useful as a supplementary marker, not first-line
• Elevated in other neuroendocrine tumors (non-specific)
• Can help confirm neuroendocrine origin

Test Hierarchy Summary

• If negative → diagnosis excluded (observe; repeat only if suspicion remains high)
• If positive → proceed to Step 2

• If positive → biochemical diagnosis confirmed → proceed to localization
• If negative/equivocal → proceed to Step 3

• Normetanephrine suppressed → essential hypertension or adrenergic excess (not pheo)
• Normetanephrine NOT suppressed → pheochromocytoma confirmed → proceed to localization

Causes of False-Positive Results

Phase 2 - Anatomical Localization

CT Scan (First-Line Anatomic Imaging)

Classic CT appearance: heterogeneously enhancing right adrenal mass. This patient had normetanephrine 28.6 nmol/L (normal <0.9) and urine normetanephrine 8760 µg/24h (normal <900 µg).

• Unenhanced HU: typically 40-50 HU (lipid-poor; adenomas are <10 HU)
• If non-contrast HU >10 → suspicious, warrants further evaluation
• Vigorous early arterial enhancement with post-contrast HU often >100
• Venous phase washout <60% (adenomas wash out >60%)
• Morphology: homogeneous (small tumors) to heterogeneous with necrosis, calcification, cystic change (large tumors)
• Can be solid, cystic, or mixed

MRI (Preferred in Specific Populations)

• Pregnant or lactating women (no radiation)
• Pediatric patients
• CT contrast allergy
• Patients declining radiation
• Extra-adrenal paraganglioma (higher MRI sensitivity)

• T2-weighted: classic "light bulb" bright signal due to high vascularity and water content - though not invariably present
• T1: isointense to hypointense relative to liver
• No chemical shift dropout on out-of-phase imaging (no lipid content - key distinction from adrenal adenoma, which loses signal on OOP)
• Post-gadolinium: vigorous enhancement
• Variable: can be homogeneous intermediate, heterogeneous with swirl pattern, or multiple pockets of T2 brightness (cystic)

Comparison: CT vs MRI for Pheo

Phase 3 - Functional Imaging

1. CT/MRI negative but biochemistry strongly positive (extra-adrenal location)
2. Suspected metastatic or multifocal disease
3. High-risk patients: SDHB mutation, large tumor (>5 cm), young age
4. Pre-treatment planning for MIBG-directed therapy

¹²³I-MIBG Scintigraphy

• MIBG (metaiodobenzylguanidine) is a structural analogue of guanethidine, taken up by the norepinephrine transporter (NET) and stored in chromaffin granules
• Sensitivity: 77-90% (adrenal); lower for SDHB-mutated and metastatic tumors
• Specificity: 95-100%
• Normal physiological uptake: liver, salivary glands, thyroid, bladder
• MIBG-negative tumors: VHL and SDHB-mutated PPGLs often show "cold" MIBG scans → use ¹⁸F-FDG PET instead
• Also used for pre-treatment staging before ¹³¹I-MIBG therapy

¹⁸F-FDG PET/CT

• Best for SDHB-mutated and metastatic disease
• Aggressive metastatic lesions that lose MIBG uptake often retain FDG avidity
• Sensitivity ~49% overall for sporadic localized pheo, but superior to MIBG for SDHB/malignant
• Particularly useful when MIBG scan is negative

¹⁸F-DOPA (F-dihydroxyphenylalanine) PET/CT

• Highly sensitive for sporadic, non-metastatic adrenal pheochromocytoma
• Sensitivity ~75%; superior to MIBG for head/neck PGL
• Less useful for SDHB-related disease

⁶⁸Ga-DOTATATE/DOTATOC PET/CT (Best Overall)

• Uses radiolabeled somatostatin analogue targeting somatostatin receptors (SSTR2) on neuroendocrine tumors
• Currently the best single functional imaging agent for PPGL localization
• Lesion detection rate: 97.6% - higher than FDG PET (49%) and ¹⁸F-FDOPA (75%)
• Particularly superior for SDHB-associated metastatic disease
• Increasingly available; previously limited to academic centers
• Also guides ¹⁷⁷Lu-DOTATATE PRRT (peptide receptor radionuclide therapy) selection

Functional Imaging Selection Guide

What NOT to Do

Additional Investigations (General + Genetic)

Routine Labs

• Electrolytes, renal function (hypokalemia may occur with dopamine excess; renal ischemia from vasoconstriction)
• Blood glucose (catecholamines inhibit insulin; hyperglycemia common)
• CBC (polycythemia in HIF2α/EPAS1 mutations)
• ECG (LVH, ST/T changes, arrhythmias from catecholamine effect)
• Echocardiogram (catecholamine cardiomyopathy evaluation before surgery)

Genetic Testing

Key Numbers to Remember

• Campbell-Walsh-Wein Urology (9780323546423), Table 106.8, pp. 3148-3154
• Sabiston Textbook of Surgery (9780443124341), Table 75.4, pp. 1571-1574
• Schwartz's Principles of Surgery 11e (9781259835346), pp. 1721-1722
• Goldman-Cecil Medicine (9780323930345), Fig. 209-1, pp. 341-355
• Current Surgical Therapy 14e (9780323796835), pp. 869-872