Pheochromocytoma

Detailed Overview

These tumors cause severe, secondary hypertension that can be sustained or paroxysmal. The classic triad of episodic headache, sweating, and tachycardia is highly suggestive but not universally present. Because of the excessive catecholamine release, patients are at high risk for fatal hypertensive crises, arrhythmias, or myocardial infarction, especially during surgery or induction of anesthesia. Genetic testing is now recommended for all diagnosed patients due to high rates of familial syndromes.

Epidemiology & Demographics

Incidence is 2-8 per million persons per year. Peaks between the 3rd and 5th decades of life. Found in about 0.2% of patients with hypertension.

Etiological Mechanism

Approximately 60% are sporadic. The remaining 40% are associated with germline mutations in susceptibility genes (RET, VHL, NF1, SDHx).

Primary Causes

Neoplastic proliferation of chromaffin cells in the adrenal medulla (90%) or extra-adrenal paraganglia (10%), commonly driven by genetic mutations (e.g., Multiple Endocrine Neoplasia type 2, von Hippel-Lindau disease, Neurofibromatosis type 1).

• Family History: A first-degree relative with a known pheochromocytoma or hereditary syndrome (MEN2, VHL, NF1).
• Known Genetic Mutation: Carriers of RET, VHL, NF1, or SDH gene mutations have a lifetime risk approaching 50% for tumor development.

Chromaffin cells synthesize catecholamines from tyrosine. In pheochromocytoma, autonomous and uncontrolled secretion of norepinephrine (binds alpha-1 receptors causing profound vasoconstriction and hypertension) and epinephrine (binds beta-1 receptors causing tachycardia and increased cardiac output) occurs. The release is often episodic due to changes in tumor blood flow, physical compression, or induction by drugs. Sustained high catecholamine levels lead to alpha-receptor downregulation and chronic volume depletion, making patients paradoxically susceptible to severe hypotension after tumor removal.

Characteristic Clinical Presentation

• Paroxysmal Headaches: Severe, sudden-onset pounding headaches during a catecholamine surge.
• Diaphoresis: Profuse, inappropriate sweating, particularly involving the trunk.
• Palpitations: Sensation of a rapid, forceful heartbeat (tachycardia).
• Anxiety and Panic: Feelings of impending doom mimicking panic attacks.

Physical Examination Signs

• Hypertension (sustained in 50-60%, paroxysmal in 30%).
• Orthostatic hypotension (due to chronic volume depletion and blunted sympathetic reflexes).
• Pallor of the face and extremities during an attack (due to severe vasoconstriction).

• Hypertensive Crisis: Blood pressure >180/120 mmHg leading to hypertensive encephalopathy or hemorrhagic stroke.
• Catecholamine-induced Cardiomyopathy: Reversible stress cardiomyopathy (Takotsubo-like) causing acute heart failure.
• Arrhythmias: Ventricular tachycardia or fibrillation due to beta-1 receptor hyperstimulation.

Diagnostic Criteria & Guidelines

Biochemical confirmation of catecholamine excess followed by anatomical localization. Diagnosis requires significantly elevated levels (usually >2-3 times the upper limit of normal) of plasma free metanephrines or 24-hour urine fractionated metanephrines.

Differential Diagnosis

• Essential Hypertension (poorly controlled)
• Panic Disorder
• Hyperthyroidism
• Cocaine or Amphetamine Intoxication

Laboratory Tests & Biomarkers

• Plasma Free Metanephrines: Elevated (e.g., Normetanephrine > 400 pg/mL or Metanephrine > 236 pg/mL). Test of choice for high suspicion.
• 24-hour Urine Fractionated Metanephrines and Catecholamines: Markedly elevated (e.g., Total metanephrines > 1800 mcg/24h). Test of choice for lower suspicion.
• Clonidine Suppression Test: Failure of plasma normetanephrine to suppress by 50% or fall below normal limits after 0.3 mg clonidine administration (used for equivocal results).

Imaging Modalities & Findings

• CT Abdomen/Pelvis with contrast: Adrenal mass, typically >3 cm, heterogeneous with areas of necrosis/cystic change, showing high unenhanced attenuation (>20 Hounsfield units) and marked contrast enhancement.
• MRI Abdomen: Hyperintense adrenal mass on T2-weighted imaging (the classic 'lightbulb' sign, though not universally present).
• MIBG Scan (123I-metaiodobenzylguanidine): Functional imaging showing radiotracer uptake in the adrenal mass or ectopic extra-adrenal tissue; highly specific.

• Benign / Localized
  Tumor confined to the adrenal gland with no evidence of metastasis (approx. 90% of cases).
• Malignant / Metastatic
  Presence of chromaffin tissue in non-chromaffin organs (e.g., bone, liver, lungs); more common with extra-adrenal or SDHB mutations.

Second-Line & Adjunctive Therapy

Metyrosine (250 mg PO QID up to 4g/day) inhibits tyrosine hydroxylase, reducing catecholamine synthesis; used for pre-op optimization in extensive/metastatic disease or if standard blockade is ineffective.

Surgical & Procedural Management

Laparoscopic adrenalectomy is the definitive treatment for localized tumors. Open adrenalectomy is reserved for large (>6 cm) or likely malignant tumors. Extreme hemodynamic monitoring during surgery is required.

Recommended Lifestyle Changes

• Increase sodium (>5g/day) and fluid intake during the alpha-blockade phase to expand intravascular volume and prevent severe post-operative hypotension.
• Avoid medications that can precipitate crises (e.g., metoclopramide, MAOIs, ephedrine).

Patient Counseling & Advice

Warn the patient that initiating beta-blockers before alpha-blockers is strictly prohibited, as it can cause unopposed alpha-adrenergic stimulation, leading to a fatal hypertensive crisis. Genetic counseling is essential post-diagnosis.

Follow-Up & Monitoring Schedule

Recheck plasma or urine metanephrines 2-6 weeks post-operatively to confirm cure. Annual biochemical screening for at least 10 years, and lifelong for those with genetic mutations or extra-adrenal tumors.

Preventive Strategies

No primary prevention exists. Secondary prevention relies on prophylactic screening of family members in cases of known hereditary syndromes (e.g., checking plasma metanephrines yearly in MEN2 gene carriers).

The 5-year survival rate for localized completely resected pheochromocytoma is >95%. For metastatic disease, 5-year survival is highly variable (40-60%). Hypertension resolves post-operatively in about 70% of patients.