Pheochromocytoma

Pheochromocytoma – High‑Yield Study Guide for Medical Students

Definition

Pheochromocytoma is a catecholamine-secreting neuroendocrine tumor that arises from chromaffin cells of the adrenal medulla and is characterized by excess production of catecholamines, mainly norepinephrine and epinephrine.⁵ Extra-adrenal tumors arising from sympathetic paraganglia are termed paragangliomas but share similar clinical behavior and diagnostic principles.

Epidemiology

Pheochromocytoma is rare, with an estimated incidence of about 2–8 cases per million per year, but it is an important cause of secondary hypertension. A significant proportion (up to 30–40%) are associated with germline mutations in susceptibility genes such as RET, VHL, NF1, and SDHx. Multiple endocrine neoplasia type 2A (MEN2A), often due to RET C634 variants, is a classic hereditary syndrome in which pheochromocytoma coexists with medullary thyroid carcinoma and primary hyperparathyroidism.^{1, 4}

Pathophysiology

Pheochromocytomas arise from neural crest–derived chromaffin cells that undergo neoplastic transformation, often driven by germline or somatic mutations affecting pathways such as RET (MEN2), VHL, and SDHx. These tumors synthesize, store, and episodically or continuously secrete catecholamines (norepinephrine, epinephrine, and sometimes dopamine). Excess catecholamines stimulate alpha- and beta-adrenergic receptors, causing vasoconstriction, tachycardia, and metabolic effects.

The biochemical phenotype can vary with tumor genetics and disease stage. In MEN2A-related pheochromocytoma, studies have demonstrated shifts in catecholamine and metabolite patterns with advancing disease, which has implications for biochemical testing and surveillance strategies.¹

Catecholamine excess leads to:

• Cardiovascular effects: systemic vasoconstriction, increased heart rate and contractility, paroxysmal or sustained hypertension, and risk of cardiomyopathy.
• Metabolic effects: increased glycogenolysis and lipolysis, impaired insulin secretion, and hyperglycemia.
• Other organ effects: splanchnic vasoconstriction and altered gut motility, predisposing to rare presentations such as pseudo-obstruction (e.g., Ogilvie syndrome).⁵

Clinical Presentation

Clinical manifestations range from classic adrenergic paroxysms to subtle, nonspecific symptoms. Many patients present with resistant or paroxysmal hypertension, but some are normotensive.

Classic Triad

• Headache – typically severe, throbbing.
• Palpitations – due to tachycardia or arrhythmias.
• Diaphoresis (profuse sweating).

This triad in the setting of episodic hypertension is highly suggestive of pheochromocytoma.

Other Symptoms and Signs

• Paroxysmal or sustained hypertension.
• Anxiety, tremor, sense of impending doom during attacks.
• Chest pain, dyspnea, or features of catecholamine-induced cardiomyopathy.
• Weight loss, heat intolerance, hyperglycemia.
• Orthostatic hypotension (from chronic vasoconstriction and volume depletion).
• Abdominal pain or flank pain if tumor is large or hemorrhagic.

Atypical and Rare Presentations

• Gastrointestinal manifestations: ileus, pseudo-obstruction, or acute colonic pseudo-obstruction (Ogilvie syndrome) due to catecholamine effects on gut motility.⁵
• Drug-triggered crises: acute hypertensive crisis precipitated by dopamine antagonists (e.g., metoclopramide), beta-blocker monotherapy, glucocorticoids, or anesthesia induction in undiagnosed patients.²
• Incidentaloma: asymptomatic adrenal mass detected on imaging done for unrelated reasons.

Diagnosis

Diagnosis rests on biochemical confirmation of catecholamine excess followed by localization of the tumor and evaluation for hereditary syndromes.

Who to Test

• Patients with paroxysmal hypertension and classic triad (headache, palpitations, diaphoresis).
• Resistant or labile hypertension, especially at a young age.
• Adrenal incidentaloma >1 cm, particularly if imaging is suggestive of pheochromocytoma.
• Known hereditary syndromes (MEN2, VHL, NF1, SDHx) or family history of pheochromocytoma/paraganglioma.⁴

Biochemical Testing

• First-line tests:
  • Plasma free metanephrines (metanephrine and normetanephrine) measured in the supine position after rest.
  • or 24‑hour urinary fractionated metanephrines and catecholamines.
• Metanephrines are more stable metabolites and provide higher sensitivity than direct catecholamine measurement.
• Marked elevations (>3× upper limit of normal) are highly suggestive of pheochromocytoma; mild elevations may require repeat testing, medication review, or clonidine suppression testing in selected cases.
• Consider biochemical phenotype patterns, which can differ by genotype and disease stage (e.g., shifts in catecholamine profiles in MEN2A-related tumors).¹

Imaging

• CT or MRI of the adrenal glands is the initial localization study once biochemical diagnosis is established.
• MRI is preferred in younger patients, pregnancy, or when radiation avoidance is desired; pheochromocytomas classically appear as hyperintense on T2-weighted images.
• Functional imaging (e.g., 123I‑MIBG scintigraphy, PET) is useful in suspected multifocal disease, extra-adrenal paraganglioma, or metastatic disease.
• In MEN2 and other hereditary syndromes, bilateral and multifocal adrenal disease is more common, which should influence imaging strategy and operative planning.^{1, 4}

Genetic Evaluation

• Given the high rate of heritable disease, many guidelines recommend genetic testing for all patients with pheochromocytoma/paraganglioma or at least those diagnosed at a young age, with multifocal/bilateral tumors, or with a positive family history.
• Identification of a RET mutation confirms MEN2; RET C634Y is a common MEN2A mutation, with reported rare homozygous and twin cases emphasising variable expressivity.⁴

Management

Definitive therapy is surgical resection of the tumor, but meticulous preoperative preparation is essential to reduce perioperative morbidity.

Preoperative Medical Optimization

• Alpha-adrenergic blockade is initiated first, usually 7–14 days before surgery:
  • Nonselective, irreversible alpha blocker (e.g., phenoxybenzamine) or selective alpha-1 blockers (e.g., doxazosin).
  • Goal: control blood pressure, reduce paroxysms, and allow volume expansion.
• Volume expansion with liberal salt and fluid intake to correct chronic catecholamine-induced vasoconstriction and reduce postoperative hypotension.
• Beta-blockers are added only after adequate alpha blockade if tachycardia or arrhythmias persist, to avoid unopposed alpha stimulation.
• Review medications that may precipitate crisis (e.g., metoclopramide, certain anesthetics) and coordinate with anesthesia team.²

Surgical Management

• Laparoscopic adrenalectomy is the standard of care for most localized adrenal pheochromocytomas.
• Open surgery may be required for very large tumors, local invasion, or suspected malignancy.
• In hereditary syndromes (e.g., MEN2), cortical-sparing adrenalectomy may be considered to reduce risk of lifelong adrenal insufficiency, especially in bilateral disease.¹

Management of Crisis

• Pheochromocytoma crisis is characterized by severe hypertension or hemodynamic instability, often triggered by drugs (e.g., metoclopramide), surgery, or stress.
• Management includes rapid control of blood pressure with titratable IV vasodilators (e.g., nitroprusside, phentolamine) and treatment in an intensive setting, followed by definitive tumor resection once stabilized.²

Follow-up and Long-Term Surveillance

• Biochemical testing (plasma or urinary metanephrines) is repeated postoperatively to confirm biochemical cure.
• Long-term surveillance is essential due to risk of recurrence, especially in hereditary cases and paragangliomas.
• In MEN2 families, ongoing screening for medullary thyroid carcinoma, hyperparathyroidism, and recurrent pheochromocytoma is required.⁴

Key Clinical Pearls for Exams and Practice

• The classic triad of episodic headache, sweating, and palpitations with paroxysmal hypertension is highly suggestive of pheochromocytoma.
• Always think pheochromocytoma in young patients with resistant or labile hypertension, especially with suggestive symptoms or adrenal incidentaloma.
• Biochemical confirmation (plasma free or urinary fractionated metanephrines) should precede imaging.
• Never start beta-blockers before alpha-blockade; this can precipitate a life-threatening hypertensive crisis due to unopposed alpha-adrenergic stimulation.
• Metoclopramide and other dopamine antagonists can precipitate pheochromocytoma crisis in undiagnosed patients; consider this in sudden hypertensive decompensation after such medications.²
• Pheochromocytoma is a classic endocrine tumor in MEN2A; RET genetic testing is indicated in affected patients and at-risk relatives.⁴
• Rare presentations include gastrointestinal dysmotility and acute colonic pseudo-obstruction (Ogilvie syndrome), reinforcing the need for a high index of suspicion in unexplained autonomic or GI crises.⁵
• In hereditary cases, anticipate bilateral or multifocal disease and consider adrenal-sparing approaches when feasible.¹

Summary

Pheochromocytoma is a rare but critical cause of secondary hypertension and catecholamine excess. For medical students, high-yield points include recognizing the classic triad, understanding the role of plasma or urinary metanephrines in diagnosis, knowing the need for alpha-blockade before surgery (and before beta-blockade), and remembering the strong association with hereditary syndromes such as MEN2A driven by RET mutations. Mastery of these concepts is essential for exams and safe clinical practice.