Pheochromocytoma
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Pheochromocytoma
A pheochromocytoma is a catecholamine-secreting tumor arising from chromaffin cells of the adrenal medulla. Together with extra-adrenal paragangliomas, these tumors are collectively termed PPGLs (pheochromocytomas and paragangliomas). Though rare (estimated 2-8 cases per million per year), they are clinically important because they can cause fatal hypertensive crises, are potentially curable with surgery, and carry a significant hereditary component.
Epidemiology & the "Rule of 10s"
The traditional "rule of 10s" describes the distribution of pheochromocytomas:
- ~10% are extra-adrenal (paragangliomas)
- ~10% are bilateral
- ~10% occur in children
- ~10% are malignant at presentation (more recent data suggests this may exceed 10%)
- ~10% are familial (this figure has substantially increased - now estimated >30-40% carry germline mutations)
Pheochromocytomas are found in 0.2%-0.6% of hypertensive patients, and may be more common in hypertensive children (~1.7%). They are discovered incidentally or, in tragic cases, only at autopsy. - Brenner and Rector's The Kidney
Pathology
Gross Morphology
Pheochromocytomas range from small circumscribed lesions to large hemorrhagic masses; the average weight is ~100 g (range: >1 g to nearly 4,000 g). Smaller tumors are yellow-tan on cut section; larger ones tend to be hemorrhagic, necrotic, and cystic. A key histochemical feature: incubation with potassium dichromate turns the tumor dark brown due to oxidation of stored catecholamines - the origin of the term "chromaffin."
Histology
The classic pattern is the "zellballen" (German: "cell balls") - clusters of polygonal to spindle-shaped chromaffin cells (chief cells) surrounded by sustentacular cells, arranged in small nests or alveoli supplied by a rich vascular network. The cytoplasm has a finely granular appearance due to catecholamine-containing granules. Nuclei show characteristic "salt-and-pepper" chromatin typical of neuroendocrine tumors. Electron microscopy reveals membrane-bound, electron-dense secretory granules.
Immunohistochemistry:
- Chief cells: positive for chromogranin and synaptophysin
- Sustentacular cells: positive for S-100
Determining Malignancy
Malignancy cannot be determined histologically. Cellular pleomorphism, mitoses, and even vascular/capsular invasion can be seen in benign tumors. Paradoxically, cellular monotony may be associated with aggressive behavior. The only reliable indicator of malignancy is the presence of metastases - to regional lymph nodes, liver, lung, or bone. - Robbins, Cotran & Kumar Pathologic Basis of Disease
Hereditary Syndromes & Genetics
More than 30% of pheochromocytomas are now associated with germline mutations. Key syndromes include:
| Syndrome | Gene | Key Features |
|---|---|---|
| MEN2A | RET proto-oncogene | Pheo (~50%, usually bilateral), medullary thyroid carcinoma, parathyroid adenomas, cutaneous lichen amyloidosis |
| MEN2B | RET | Bilateral pheo, medullary thyroid Ca, submucosal neuromas, marfanoid body habitus, Hirschsprung disease |
| Von Hippel-Lindau (VHL) type 2 | VHL (chr 3p25-26) | Pheo/paraganglioma in ~20%, retinal/cerebellar hemangioblastomas, clear cell RCC, pancreatic NET |
| Neurofibromatosis type 1 | NF1 (chr 17q11.2) | Pheo in ~2%, neurofibromas, café-au-lait spots, Lisch nodules |
| Familial paraganglioma | SDHB (chr 1p35-36), SDHD (chr 11q23) | Paragangliomas of skull base, neck, thorax, abdomen, bladder |
| Sturge-Weber | GNAQ | Port wine stain, leptomeningeal angiomas |
Current guidelines recommend genetic testing for all patients with pheochromocytoma, with a shared decision-making process often involving family members. - Brenner and Rector's The Kidney
Molecular Clusters
Tumors are broadly divided into two molecular clusters based on secretory behavior:
- Cluster 1 (noradrenergic): VHL, SDHB, SDHD mutations - constitutive, Ca2+-independent secretory pathway; predominantly norepinephrine
- Cluster 2 (adrenergic): MEN2, NF1 - regulated, Ca2+-dependent secretory pathway; produce both epinephrine and norepinephrine
Clinical Features
Symptoms
The classic triad is: headache, sweating, and hypertension (reported in ~95% in large series). Other features include:
- Tachycardia and palpitations
- Tremor and sense of apprehension
- Abdominal or chest pain, nausea, vomiting
- Pallor (due to vasoconstriction)
Hypertension is present in ~90% of patients. Approximately two-thirds experience paroxysmal episodes - abrupt, precipitous BP elevation superimposed on chronic hypertension. Isolated paroxysms without sustained hypertension occur in less than half.
Precipitants of paroxysms: emotional stress, exercise, posture change, tumor palpation, micturition (bladder paragangliomas), certain drugs (metoclopramide, beta-blockers, glucocorticoids, histamine, tyramine).
Cardiac Complications
- Congestive heart failure, pulmonary edema, myocardial infarction, ventricular fibrillation, stroke
- Catecholamine cardiomyopathy: focal myocardial necrosis, mononuclear infiltrates, and interstitial fibrosis due to catecholamine-induced vasospasm or direct catecholamine toxicity
- One of the most dangerous presentations is unexplained shock, possibly followed by multisystem organ failure
- Pheo in pregnancy masquerading as preeclampsia carries high maternal and fetal mortality if undiagnosed
Differential Diagnosis
Many conditions mimic pheochromocytoma:
- Anxiety disorders and panic attacks
- Essential hypertension
- Hyperthyroidism
- Carcinoid syndrome
- Systemic mastocytosis
- Migraine/cluster headaches
- Baroreflex failure, POTS
- Factitious (self-administered catecholamines)
Clues from physical exam: café-au-lait spots/neurofibromas (NF1), retinal hemangiomas (VHL), port wine stain (Sturge-Weber), subungual fibromas/ash leaf patches (tuberous sclerosis), marfanoid habitus (MEN2B). - Brenner and Rector's The Kidney
Biochemical Diagnosis
The first critical step is simply thinking of the tumor. Given the rarity and many mimics, clinical suspicion must be high.
Preferred tests:
- Plasma free metanephrines - highest sensitivity; brief snapshot of catecholamine production and metabolism. Preferred when rapid, accurate assay is available.
- 24-hour urinary fractionated metanephrines - integrates catecholamine production over time; more widely available and less costly.
Why metanephrines rather than catecholamines themselves?
Pheochromocytomas continuously O-methylate catecholamines to metanephrines within the tumor (even between episodic secretory bursts), so metanephrines provide more consistent elevation than the parent catecholamines.
Causes of false-negative results: familial tumors, normotensive tumors, dopamine-beta-hydroxylase deficiency, intermittently secreting tumors.
Pharmacologic testing (used in equivocal cases):
- Clonidine suppression test (preferred) - failure of clonidine to suppress plasma norepinephrine supports the diagnosis
- Glucagon stimulation (rarely used due to risk)
The definitive diagnosis of malignancy requires evidence of metastasis. - Tietz Textbook of Laboratory Medicine, 7th Edition
Imaging & Localization
Imaging is ordered ONLY after biochemical confirmation - to improve cost-effectiveness and reduce radiation exposure.
| Modality | Notes |
|---|---|
| CT (adrenal, thin cuts) | First-line; high resolution for adrenal and peri-adrenal tissue |
| MRI | Preferred for extra-adrenal, pelvic, bladder locations; avoids radiation; pheo appears bright on T2 |
| 123I-MIBG scintigraphy | Functional imaging; useful for locating extra-adrenal and metastatic disease; confirms catecholamine-synthesizing tissue |
| FDG-PET | Particularly useful for SDHB-mutated tumors and metastatic disease |
| 68Ga-DOTATATE PET | Increasingly used for paragangliomas |
Extra-adrenal paragangliomas most commonly occur at the organ of Zuckerkandl (aortic bifurcation) or near the bladder. - Brenner and Rector's The Kidney
Treatment
Preoperative Preparation (Critical)
Proper pharmacologic preparation is essential for safe surgery:
- Alpha-blockade first - phenoxybenzamine (long-acting, irreversible) orally, or phentolamine IV. Start 7-14 days before surgery to normalize BP, HR, and intravascular volume.
- Beta-blockers second (only after adequate alpha-blockade is established) - to control tachycardia. Never start beta-blockers alone, as this can cause paradoxical hypertension from unopposed alpha-stimulation.
- Volume expansion - liberal salt and fluid intake pre-operatively to prevent postoperative hypotension.
- Calcium channel blockers - often added before beta-blockers.
- Metyrosine (tyrosine hydroxylase inhibitor) - occasionally used for very large tumors or nonsurgical candidates to reduce catecholamine synthesis.
Intraoperative Management
- Anticipate hypertensive episodes during tumor manipulation
- IV agents with rapid onset/short half-life: nitroprusside, phentolamine, nitroglycerin, nicardipine
- Short-acting beta-blockers: labetalol, esmolol
- Aggressive fluid management upon tumor removal to counter sudden loss of tonic vasoconstriction
Postoperative Management
- Monitor for hypotension (guided by invasive monitoring; phenylephrine and fluids)
- Correct hypoglycemia (rebound from loss of catecholamine-mediated glycogenolysis)
- Electrolyte correction
- Persistent hypertension is not uncommon and may require continued antihypertensives
Surgical Approach
- Laparoscopic adrenalectomy is preferred for small, localized adrenal pheochromocytomas
- Open approach for large or locally invasive tumors
- Recent evidence: A 2025 systematic review and meta-analysis (PMID 40214691) examined outcomes of partial adrenalectomy for pheochromocytoma, relevant for bilateral or hereditary cases to preserve adrenocortical function.
Follow-Up
- Repeat biochemical testing 4-6 weeks post-operatively to confirm complete resection
- Annual or individualized long-term surveillance, especially with hereditary syndromes
- Metastatic disease: treated with MIBG therapy, sunitinib, chemotherapy (cyclophosphamide/vincristine/dacarbazine regimen), or PRRT (peptide receptor radionuclide therapy) - Campbell Walsh Wein Urology; Brenner and Rector's The Kidney
Summary Table
| Feature | Detail |
|---|---|
| Origin | Adrenal medulla chromaffin cells |
| Incidence | 2-8/million/year |
| Classic triad | Headache, sweating, hypertension |
| Hypertension | ~90% of patients |
| Malignancy diagnosis | Metastases only (histology unreliable) |
| Preferred biochemical test | Plasma free metanephrines or 24-hr urinary fractionated metanephrines |
| First-line imaging | CT (after biochemical confirmation) |
| Key preop drug | Alpha-blocker (phenoxybenzamine) FIRST |
| Surgery | Laparoscopic adrenalectomy (preferred for small tumors) |
| Hereditary proportion | >30% carry germline mutations |
| Malignancy marker | Distant metastases (lymph nodes, liver, lung, bone) |
Sources: Robbins, Cotran & Kumar Pathologic Basis of Disease; Brenner and Rector's The Kidney; Tietz Textbook of Laboratory Medicine, 7th Edition; Campbell Walsh Wein Urology; Fuster and Hurst's The Heart, 15th Edition.
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