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KEY FACTS

Terminology
- Rare catecholamine-secreting tumor arising from chromaffin cells of adrenal medulla
- Termed paraganglioma if extraadrenal
Imaging
- Best diagnostic clue - Adrenal mass in setting of clinical symptoms or biochemical abnormality - Paroxysmal headache, palpitations, sweating - ↑ levels of 24-hour urine-fractionated metanephrines
- "Imaging chameleon": Variable US/CT/MR appearance; mimics other lesions - Commonly solid and hypervascular ± cystic change, necrosis, and calcification - Can be purely cystic
- 1st line: CT or MR
- US: Comparable to CT in detecting adrenal tumors; limited for extraadrenal disease
- I-123 MIBG: For extraadrenal, metastatic, or recurrent disease
Top Differential Diagnoses
- Adrenal adenoma
- Adrenal metastases or lymphoma
- Adrenocortical carcinoma
- Adrenal neuroblastoma
- Adrenal granulomatous infection
Diagnostic Checklist
- Remembered as "r****ule of 10s" - 10% extraadrenal (paraganglioma) - 10% bilateral (suggest hereditary disease) - 10% pediatric (suggest hereditary disease) - 10% contain calcification - 10% malignant (↑ extraadrenal cases) - 25% familial (previously thought to be 10%)

TERMINOLOGY

Definitions
- Paraganglioma: Neuroendocrine tumor arising from paraganglia anywhere in sympathetic chain
- Pheochromocytoma: Adrenal medullary paraganglioma arising from catecholamine-secreting chromaffin cells of adrenal medulla

IMAGING

General Features

Best diagnostic clue

- Adrenal mass in setting of clinical symptoms or biochemical abnormality

Location

- Paragangliomas can occur along sympathetic chain from neck to urinary bladder
- Majority are subdiaphragmatic (98%)
        - Adrenal (90%)
        - Extraadrenal (10%)
                  - Organ of Zuckerkandl, 2.5% [from superior mesenteric artery (SMA) to aortic bifurcation, mostly around inferior mesenteric artery]
                  - Urinary bladder sympathetic chain, 1%
- Typically unilateral
- Bilateral: Commonly with hereditary conditions

Size

- Variable: Typically 3-5 cm (can be up to 15 cm)

Morphology

- Well-circumscribed, encapsulated tumor
- Variable size and appearance on morphology and imaging renders name "chameleon tumors"
        - Commonly solid and hypervascular ± cystic change, necrosis, and calcification
        - Can be purely cystic
- Pheochromocytomas and paragangliomas demonstrate similar imaging features but vary in location

Ultrasonographic Findings

Grayscale ultrasound

- Variable appearance: Solid (75%) > solid/cystic or cystic
        - Iso-/hypoechoic (75%) or hyperechoic (25%) to renal cortex
- Small tumors: Solid, well-circumscribed; uniform echoes → can be poorly delineated due to obscuration from overlying bowel gas
- Large tumors: Solid, heterogeneous, or homogeneous echotexture
        - Heterogeneity due to necrosis (hypoechoic) and hemorrhage (hyperechoic)
- Can be predominantly cystic due to chronic hemorrhage and necrotic debris (fluid-fluid level)
- Always evaluate bladder wall, renal hilum, and organ of Zuckerkandl at origin of inferior mesenteric artery (CT more sensitive)

Color Doppler

- Hypervascular ± heterogeneous
- Compression/invasion of inferior vena cava (IVC)/renal vein
        - Seen with both benign and malignant tumors

CT Findings
- NECT: Well-defined mass with low soft tissue attenuation - Generally attenuation > 10 HU; however, rarely intracellular fat may result in lower attenuation → posing challenge to differentiate from adenoma - ± ↑ density (hemorrhage), ↓ density (cystic degeneration; necrosis), calcification (rare; 10%)
- CECT: Marked enhancement; may be heterogeneous due to hemorrhage/necrosis - Variable washout characteristics: Can show rapid washout that mimics adenoma - No convincing evidence that IV injection of iodinated contrast precipitates hypertensive crisis
MR Findings
- T1WI: Isointense to muscle and hypointense to liver - Variable signal intensity if necrosis/hemorrhage present - Rarely, contain microscopic fat on chemical shift imaging, mimicking adenoma
- T2WI: T2 hyperintense due to ↑ water content (cystic/liquefactive necrosis) - Classic light bulb appearance of marked T2-bright signal intensity (SI), variably (present in up to 2/3) - 35% have low T2 SI (isointense to spleen) - Most common: Heterogeneously enhancing lesion with multiple high-SI pockets
- T1WI C+: Characteristic salt and pepper pattern - Salt (enhancing parenchyma); pepper (↑ vascular flow voids due to hypervascular tumor)
Nuclear Medicine Findings
- 1st line: I-123 metaiodobenzylguanidine (MIBG) - Norepinephrine analog - After 24-72 hours: ↑ uptake of I-123 MIBG in tumor - Useful for extraadrenal, metastatic, recurrent disease - Sensitivity (77-90%); specificity (95-100%)
- 2nd line: 111In-pentetreotide FDG PET
- F-18 fluorodopamine, F-18 dihydroxyphenylalanine (DOPA) analogs

Imaging Recommendations

Best imaging tool

- **NE + CECT**: Overall 93-100% sensitive; however, up to 40% of extraadrenal lesions may be missed on CT
- **I-123 MIBG**: Superior detection of extraadrenal, metastatic, &/or recurrent disease
- US limited for smaller adrenal tumors; poor sensitivity for extraadrenal lesions

Protocol advice

- Include aortic bifurcation in CT/MR FOV to evaluate for paragangliomas (along sympathetic chain)

DIFFERENTIAL DIAGNOSIS

Adrenal Adenoma
- Most common benign adrenal lesion
- Pheochromocytomas tend to be larger than adenomas
- Cystic and rare microscopic fat-containing pheochromocytomas may also be hypodense on NECT
- Adenoma: Characteristic CT washout and MR signal dropout (majority)
Adrenal Metastases
- Most common malignant adrenal neoplasm (up to 25%)
- Typically bilateral; delayed contrast washout
Adrenal Lymphoma
- Large infiltrative, bilateral masses; maintain adrenal contour
- 25% secondary to non-Hodgkin lymphoma; primary is rare
Adrenocortical Carcinoma
- Rare; aggressive; large, unilateral, heterogeneous solid mass with necrosis; hemorrhage ± calcification
- T2 hyperintense and T1 hypointense to liver (as with "classic" pheochromocytomas)
- Aggressive, often with IVC extension
Adrenal Neuroblastoma
- Large pediatric adrenal mass; calcification (80-90%)
Adrenal Granulomatous Infection
- TB, histoplasmosis, other fungal diseases; usually bilateral - Acute (hypoechoic masses) or chronic (small and calcified)

PATHOLOGY

General Features

Associated abnormalities

- Majority are sporadic
- 25% have autosomal dominant gene mutation
        - **Multiple endocrine neoplasia type 2 (MEN2)**
                  - *MEN2*mutation; 50% have pheochromocytoma
                  - Medullary thyroid carcinoma, hyperparathyroidism, neuromas, and marfanoid habitus
        - **von Hippel-Lindau (VHL) disease**
                  - *VHL*tumor suppressor gene; 10-25% risk
                  - Multiple benign and malignant tumors
        - **Neurofibromatosis type 1**
                  - Rare cause of pheochromocytomas; 1% risk
                  - Cutaneous/plexiform neurofibromas, optic nerve gliomas, peripheral nerve sheath tumors, gastrointestinal stromal tumors
        - **Pheochromocytoma-paraganglioma syndromes**
                  - Mutations of succinate dehydrogenase gene family; 50% risk
                  - ↑ incidence of extraadrenal tumors and head/neck paragangliomas

Most are benign; 10% are malignant - Diagnosis of malignancy is based solely on presence of direct local tumor invasion or metastatic disease - Extraadrenal paragangliomas are more likely to be malignant

Gross Pathologic & Surgical Features
- Small tumor: Well-circumscribed, yellow-tan lesion confined to adrenals
- Large tumor: Hemorrhagic, cystic/necrotic masses
Microscopic Features
- Predominantly chromaffin cells; occasionally spindle cells are dominant feature - Term pheochromocytoma refers to dusky color of cells stained with chromium salts
- No single histologic feature of pheochromocytoma consistently predicts malignancy - Definitive pathologic diagnosis of malignancy is based on presence of metastatic disease

CLINICAL ISSUES

Presentation

Most common signs/symptoms

- Majority are asymptomatic; symptoms may be episodic or paroxysmal
- Classic triad (arises from adrenergic excess)
        - Paroxysmal headache, palpitations, sweating
        - 90% specific but uncommon (only present in 10.0-36.5% of patients)

Other signs/symptoms

- Hypertensive crisis: Palpitations, tremors, arrhythmias, pain, myocardial infarction

Laboratory data - Tumors typically secrete norepinephrine > epinephrine - **↑**levels of 24-hour urine-fractionated metanephrines - 90-97% sensitivity; 69-98% specificity

Demographics

Age

- Sporadic cases, 3rd and 4th decades
- Hereditary cases, 3rd decade
- 10% are found in children

Sex

- Slight female predilection (M:F = 1:1.4)

Epidemiology

- Exact incidence: Unknown
        - Prevalence in hypertensive adults 0.1-0.6%
- Majority of pheochromocytomas are likely asymptomatic (incidentalomas)

Natural History & Prognosis
- Hypertensive crises and cardiovascular complications ↑ morbidity/mortality
- Prognosis: Noninvasive and nonmetastatic: Typically favorable
Treatment
- Symptomatic therapy: α-adrenergic blockade and calcium channel antagonists
- Laparoscopic resection/debulking for both benign and malignant tumors
- Adjuvant therapy (malignant tumors): I-131 MIBG therapy ± chemotherapy (cyclophosphamide, vincristine, dacarbazine)

DIAGNOSTIC CHECKLIST

Consider
- Imaging can mimic other diagnoses; labs essential for diagnosis
Image Interpretation Pearls
- Extraadrenal tumors arise anywhere along sympathetic ganglia (neck to bladder), attention to these locations

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References

Selected References

Images

Selected Images

Graphic shows a typical pheochromocytoma , moderate in size with a well-circumscribed margin and solid appearance. Note hypervascularity of the mass, which commonly results in necrosis and cystic change.

Transverse (left) and longitudinal (right) transabdominal ultrasound show a well-demarcated, heterogenous, solid right adrenal mass hyperechoic to the renal cortex , proven to be a pheochromocytoma.

Longitudinal transabdominal ultrasound demonstrates well-circumscribed, round, heterogeneous, hypoechoic mass in the right suprarenal region medially, proven to be a paraganglioma.

Axial CECT in the previous patient shows a well-circumscribed, round, heterogeneous, hypodense mass , anteromedial to the upper pole right kidney , proven to be a paraganglioma.

Longitudinal transabdominal ultrasound shows a large left adrenal mass , slightly heterogeneous and hypoechoic to the renal cortex .

Axial CECT in the same patient confirms the left adrenal mass , along with right adrenal mass and a liver lesion , confirmed lung cancer metastases.

Axial T2WI MR shows 2 well-circumscribed, paraaortic paragangliomas .

Corresponding axial T1WI C+ FS MR demonstrates the same paragangliomas . Notice the salt and pepper appearance of the right-most paragangliomas, consisting of enhancing parenchyma and internal flow void (hypervascularity).

Transverse transabdominal color Doppler ultrasound shows heterogenous, hypervascular mass anteromedial to the left kidney, confirmed paraganglioma.

Axial arterial-phase CECT in the same patient confirms a large heterogeneously enhancing mass in the left retroperitoneum , confirmed paraganglioma.

Additional Images

Transverse transabdominal color Doppler ultrasound of a right adrenal pheochromocytoma shows a well-defined, heterogenous mass .

Coronal CECT shows a large, well-defined mass with avidly enhancing solid portions and large, hypodense areas of necrosis , confirmed paraganglioma.

Axial fused PET/CT demonstrates ↑ radiotracer uptake within the solid portions of the paraganglioma, whereas the necrotic areas appear photopenic . The mass is distinct from the left kidney , but notice abutment/narrowing of the main left renal vein .

Transverse color Doppler ultrasound shows a right adrenal pheochromocytoma displacing and compressing the inferior vena cava .

Axial CECT shows a large, well-circumscribed, moderately enhancing right adrenal pheochromocytoma with hypodense area of necrosis .

DTPA-MIBG scan of the same patient shows uptake within the pheochromocytoma . Note DTPA uptake in kidneys . MIBG is useful to detect extraadrenal tumors.

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KEY FACTS

Terminology

Imaging

Top Differential Diagnoses

Diagnostic Checklist

TERMINOLOGY

Definitions

IMAGING

General Features

Best diagnostic clue

Location

Size

Morphology

Ultrasonographic Findings

Grayscale ultrasound

Color Doppler

CT Findings

MR Findings

Nuclear Medicine Findings

Imaging Recommendations

Best imaging tool

Protocol advice

DIFFERENTIAL DIAGNOSIS

Adrenal Metastases

Adrenocortical Carcinoma

Adrenal Neuroblastoma

Adrenal Granulomatous Infection

PATHOLOGY

General Features

Associated abnormalities

Gross Pathologic & Surgical Features

Microscopic Features

CLINICAL ISSUES

Presentation

Most common signs/symptoms

Other signs/symptoms

Demographics

Age

Sex

Epidemiology

Natural History & Prognosis

Treatment

DIAGNOSTIC CHECKLIST

Consider

Image Interpretation Pearls

References

Selected References

Images

Selected Images

Additional Images

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