Pheochromocytoma is a catecholamine-secreting neuroendocrine tumor originating from the adrenal medulla. It is characterized by the triad of paroxysmal hypertension, headache, sweating, and palpitations. The classic '10% rule' is known: 10% bilateral, 10% extra-adrenal (paraganglioma), 10% malignant, 10% in childhood, 10% hereditary — however genetic studies have shown the hereditary rate is up to 40% (SDH, VHL, MEN2, NF1 mutations). On MRI, markedly hyperintense T2 signal ('light bulb sign') is characteristic. Biopsy is ABSOLUTELY CONTRAINDICATED — can cause catecholamine crisis and death. Diagnosis is confirmed biochemically (plasma free metanephrines).
Age Range
20-60
Peak Age
40
Gender
Equal
Prevalence
Uncommon
Pheochromocytoma originates from chromaffin cells located in the adrenal medulla. These cells are neural crest-derived and normally synthesize catecholamines (epinephrine, norepinephrine, dopamine). Tumor cells produce catecholamines uncontrollably, causing paroxysmal or sustained catecholamine discharge. Catecholamine activation of α and β adrenergic receptors produces hypertension, tachycardia, sweating, headache, and metabolic disturbances. The pathophysiological basis of imaging findings: the marked T2 hyperintensity on MRI results from the tumor's high vascularity, myxoid stroma, large extracellular water pools, and cystic/necrotic changes — these large water compartments provide long T2 relaxation time. High attenuation (>20 HU) and avid enhancement on CT reflect the rich vascular architecture. MIBG (meta-iodobenzylguanidine) scintigraphy uptake results from tumor cells actively taking up MIBG via the norepinephrine transporter (NET) — MIBG is a norepinephrine analog and is stored in chromaffin vesicles.
The marked hyperintensity shown by pheochromocytoma on MRI T2-weighted images is called 'light bulb brightness' or 'light bulb sign.' This name comes from the lesion's bright signal intensity on T2 resembling a lit light bulb. This finding is a direct result of pheochromocytoma's myxoid stroma, high vascularity, and large extracellular water pools prolonging T2 relaxation. It is seen in 65-75% of all pheochromocytomas. Sensitivity is 65-75%, specificity approximately 85-90%. In an adrenal mass showing marked T2 hyperintensity with negative washout and negative chemical-shift, pheochromocytoma is the most likely diagnosis and biochemical confirmation is mandatory.
On T2-weighted images, pheochromocytoma shows markedly hyperintense signal compared to surrounding tissues and especially the spleen — known as 'light bulb brightness' or 'light bulb sign.' This is the most characteristic imaging finding for pheochromocytoma. Signal intensity may approach cerebrospinal fluid. However, this finding is not present in all pheochromocytomas — particularly in lesions with cystic degeneration or hemorrhage, appearance may be heterogeneous. T2 hyperintensity can also be seen in some metastases, so it is not pathognomonic alone but is highly suggestive.
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On T2-weighted images, the adrenal lesion shows markedly hyperintense signal ('light bulb sign'), highly suggestive of pheochromocytoma; biochemical confirmation (plasma metanephrines) is recommended.
On non-contrast CT, pheochromocytoma typically shows attenuation >20 HU (typically in the 20-40 HU range). Does not meet the <10 HU threshold for lipid-rich adenoma. The lesion may be heterogeneous — containing cystic areas, hemorrhagic foci, and calcification. Size is usually 3-5 cm but can be very large (>10 cm). Calcification is seen in 10-15% of cases.
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A heterogeneous adrenal mass measuring approximately ___ cm in the left/right adrenal gland demonstrates ___ HU attenuation on non-contrast CT, containing areas of cystic degeneration and/or calcification.
In the arterial phase, pheochromocytoma shows avid, heterogeneous enhancement. Solid components enhance markedly while cystic/necrotic areas do not enhance. Enhancement intensity reflects the tumor's high vascularity and is generally more intense than adenoma enhancement. 'Ring enhancement' (peripheral enhancement) may be seen — reflecting viable peripheral tumor tissue surrounding central necrosis or cystic degeneration.
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In the arterial phase, the lesion demonstrates avid, heterogeneous enhancement, with central cystic/necrotic areas remaining unenhanced.
On delayed phase, pheochromocytoma shows slow washout — absolute washout <60% and relative washout <40%. This is distinctly different from adenoma's rapid washout (>60%) and is of critical importance in differential diagnosis. Slow washout results from contrast pooling in the interstitium longer due to irregular vessels and increased vascular permeability in tumor neovascularization.
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On delayed phase, the lesion shows slow washout (absolute washout: __%, relative washout: __%), this kinetic profile is consistent with pheochromocytoma and argues against adenoma.
On MRI chemical-shift sequences, pheochromocytoma does not show signal drop on opposed-phase images. This reflects its solid structure without intracellular lipid and is the key differentiating finding from lipid-rich adenoma. The combination of chemical-shift negative + T2 hyperintense + slow washout is the characteristic triad for pheochromocytoma.
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No signal drop is seen on opposed-phase chemical-shift images, indicating absence of intracellular lipid; this finding argues against adenoma and favors pheochromocytoma.
On DWI, pheochromocytoma shows variable diffusion restriction. Mild-to-moderate diffusion restriction may be seen in solid components. Diffusion may be free in cystic/necrotic areas. ADC values are heterogeneous, ranging from 0.8-1.5 × 10⁻³ mm²/s in solid regions. DWI is not a primary tool for pheochromocytoma diagnosis but provides complementary information.
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On DWI, the lesion shows heterogeneous diffusion pattern, with mild diffusion restriction in solid components and free diffusion in cystic areas.
On I-123 or I-131 MIBG scintigraphy, pheochromocytoma shows avid uptake. MIBG is a norepinephrine analog actively taken up by chromaffin cells via the norepinephrine transporter (NET) and stored in catecholamine storage vesicles. Sensitivity is 85-95%, specificity 95-100%. I-123 MIBG provides higher image quality than I-131 (better with SPECT/CT). In MIBG-negative cases (5-15%), 68Ga-DOTATATE PET-CT or 18F-FDOPA PET-CT are alternative functional imaging options.
Report Sentence
On I-123 MIBG scintigraphy, avid uptake is observed in the left/right adrenal lesion, supporting the diagnosis of pheochromocytoma; extra-adrenal uptake areas should be evaluated.
On FDG PET-CT, pheochromocytoma shows variable FDG uptake — most cases show uptake above liver SUV. SDH-mutant pheochromocytomas typically show very high FDG uptake. However, some pheochromocytomas may have low FDG uptake. FDG PET-CT is used especially for staging in metastatic pheochromocytoma and localization in MIBG-negative cases.
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On FDG PET-CT, increased FDG uptake is observed in the adrenal lesion (SUVmax: ___); whole-body evaluation should be performed for metastatic disease.
Criteria
No hereditary syndrome association. 60% of all pheochromocytomas. Usually unilateral, solitary. Mean age at diagnosis 40-50.
Distinct Features
Genetic testing recommended in all cases (ESE 2016 guideline). Even sporadic cases may carry 15-20% germline mutations. Laparoscopic adrenalectomy is standard treatment.
Criteria
RET proto-oncogene mutation. MEN2A: pheochromocytoma + medullary thyroid carcinoma + hyperparathyroidism. MEN2B: pheochromocytoma + medullary thyroid carcinoma + mucosal neuromas + marfanoid habitus. 50% bilateral.
Distinct Features
Bilateral adrenalectomy requires lifelong steroid replacement. Cortical-sparing adrenalectomy (partial) is an alternative. Simultaneous screening of thyroid and parathyroid needed.
Criteria
VHL gene mutation. VHL type 2: pheochromocytoma + renal RCC + cerebellar/spinal hemangioblastoma + retinal angiomatosis + pancreatic cysts. 40% bilateral.
Distinct Features
Predominantly secretes norepinephrine (low epinephrine). MIBG sensitivity may be slightly lower. Multiorgan screening (kidney, CNS, retina, pancreas) needed. Usually diagnosed at young age.
Criteria
SDHA/B/C/D or SDHAF2 mutation. Extra-adrenal paraganglioma common (especially SDHB). SDHB: malignancy risk 30-40% (highest). May be bilateral. May be multifocal.
Distinct Features
Very high FDG PET-CT uptake (Warburg effect — mitochondrial dysfunction). MIBG may be negative. 68Ga-DOTATATE PET-CT may be preferred. Lifelong follow-up mandatory (high malignancy and recurrence risk).
Distinguishing Feature
Lipid-poor adenoma is isointense/mildly hyperintense on T2 (no light bulb sign), shows rapid washout (>60%). Pheochromocytoma is markedly hyperintense on T2, slow washout (<60%). Plasma metanephrines elevated in pheochromocytoma, normal in adenoma.
Distinguishing Feature
Metastasis shows variable T2 signal (usually mild-moderate hyperintense), slow washout, MIBG negative, known primary malignancy history. Pheochromocytoma markedly hyperintense on T2, MIBG positive, plasma metanephrines elevated.
Distinguishing Feature
Adrenocortical carcinoma usually >6 cm, irregular margins, invasion signs, virilization/Cushing. Heterogeneous on T2 (marked hyperintensity rare). Catecholamine elevation, MIBG positivity, and paroxysmal symptoms distinguish pheochromocytoma.
Distinguishing Feature
Ganglioneuroma shows variable T2 signal (usually homogeneous moderate hyperintensity), late progressive enhancement, non-functional. Pheochromocytoma brighter on T2, avid arterial enhancement, catecholamines elevated.
Urgency
urgentManagement
surgicalBiopsy
Not NeededFollow-up
annualPheochromocytoma requires urgent management — untreated catecholamine crisis can lead to hypertensive crisis, myocardial infarction, cerebrovascular event, and death. BIOPSY IS ABSOLUTELY CONTRAINDICATED — needle biopsy can trigger catecholamine discharge. Diagnosis is confirmed biochemically: plasma free metanephrines (>97% sensitivity, >93% specificity). Preoperative alpha-adrenergic blockade (phenoxybenzamine or doxazosin) must be started at least 10-14 days before surgery — beta-blockade is then added (beta-blockade without alpha-blockade is contraindicated). Laparoscopic adrenalectomy is curative. Postoperative hypotension and hypoglycemia risk exists. Genetic testing is recommended in all cases (SDH, VHL, MEN2, NF1). Malignant pheochromocytoma (10-15%) is defined by metastatic disease (bone, liver, lung, lymph node). Lifelong follow-up is required — recurrence risk 5-15%.
Biochemical confirmation (plasma/urine metanephrines) is essential for pheochromocytoma diagnosis. Pre-surgical alpha-blockade is mandatory. May be associated with hereditary syndromes (MEN 2, VHL, NF1, SDH mutations).