Diagnostic Ultrasound - Abdomen and Pelvis

Pheochromocytoma
TERMINOLOGY
Definitions
• Paraganglioma: Neuroendocrine tumor arising from
paraganglia anywhere in sympathetic chain
• Pheochromocytoma: Adrenal medullary paraganglioma
○ Arises 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 occur along sympathetic chain: Neck to
urinary bladder
○ Majority are subdiaphragmatic (98%)
– Adrenal (90%); extraadrenal (10%)
□ Aortic bifurcation: Organ of Zuckerkandl, 2.5%
○ Typically unilateral
○ Bilateral: Commonly with hereditary conditions; 10% of
sporadic cases
• Size
○ Variable: Up to 15 cm (typically 3-5 cm)
• Morphology
○ Well-circumscribed, encapsulated tumor
○ Variable size & appearance, "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 (77%) or hyperechoic (23%) to kidney
○ Small tumors: Solid, well-circumscribed; uniform echoes
○ Large tumors: Solid; homogeneous (46%) or
heterogeneous (54%) echo pattern
– Complex echo pattern: Necrosis (hypoechoic) &/or
hemorrhage (hyperechoic)
○ Can be predominantly cystic lesions due to chronic
hemorrhage and necrotic debris (fluid-fluid level)
○ Overlying bowel gas can obscure extraadrenal masses
○ Always evaluate bladder wall, renal hilum, and organ of
Zuckerkandl at origin of inferior mesenteric artery
• Color Doppler
○ Hypervascular
○ Compression/invasion of IVC/renal vein
– Seen with both benign & 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
○ ±: ↑ 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 (previous belief)
MR Findings
• T1WI: Isointense to muscle & hypointense to liver
○ Variable signal intensity if necrosis/hemorrhage present
○ If microscopic fat present (rare), chemical shift signal loss
may mimic adenoma
• T2WI: T2 hyperintense due to ↑ water content
(cystic/liquefactive necrosis)
○ Classic "light-bulb" appearance of marked T2-bright SI,
variably seen (11-65%)
○ 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
• First-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 (79-88%); specificity (~ 100%)
• 2nd line: In-111 Pentetreotide, FDG PET, DOPA analogs
Imaging Recommendations
• Best imaging tool
○ US: Comparable sensitivity to CT for detection of adrenal
disease; poor detection of extraadrenal tumors
○ NE + CECT: Overall 93-100% sensitive; however, up to
40% extraadrenal lesions may be missed on CT
○ I-123 MIBG: Superior detection of extraadrenal,
metastatic, &/or recurrent disease
• Protocol advice
○ Include aortic bifurcation in CT/MR field of view to
evaluate for paragangliomas
DIFFERENTIAL DIAGNOSIS
Adrenal Adenoma
• Most common adrenal lesion; benign
• Pheochromocytomas tend to be larger than adenomas
• Cystic and rare microscopic fat-containing
pheochromocytomas may also be hypodense on NECT
• Adenoma: Characteristic CT washout & MR signal dropout
Adrenal Metastases
• Most common malignant adrenal neoplasm (27% of all
cancer)
• Typically bilateral; delayed contrast washout
Adrenal Lymphoma
• Large infiltrative, bilateral masses; adrenals maintain shape
• 25% secondary to non-Hodgkin lymphoma; primary is rare
Diagnoses: Adrenal Gland
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