What are the considerations and protocols for using CT (Computed Tomography) adrenaline (epinephrine) imaging in patients with suspected pheochromocytoma, particularly those with cardiovascular disease?

CT Imaging for Pheochromocytoma: Protocol and Safety Considerations

For patients with suspected pheochromocytoma requiring CT imaging, use nonionic contrast agents which are safe and do not increase the risk of hypertensive crisis, but biochemical confirmation with plasma free metanephrines or 24-hour urinary fractionated metanephrines must always be obtained before any imaging study. 1, 2

Pre-Imaging Requirements

Biochemical testing is mandatory before proceeding with any imaging or invasive procedures:

• Measure plasma free metanephrines (preferred) or 24-hour urinary fractionated metanephrines to confirm catecholamine excess 1, 2
• This step is critical to avoid triggering a potentially fatal hypertensive crisis during procedures 1, 2
• Never perform fine needle biopsy before excluding pheochromocytoma biochemically 1, 2

CT Technical Protocol

Initial non-contrast CT is the mandatory first imaging study:

• Obtain unenhanced CT of the abdomen as the primary diagnostic approach 2
• Use 100-130 kV with mAs modulation for optimal image quality 3
• Measure Hounsfield units (HU): lesions >10 HU require further evaluation as they are suspicious for pheochromocytoma 2, 3
• Include chest CT concurrently to evaluate for metastatic disease or extra-adrenal locations 2

For biochemically confirmed cases:

• SPECT/CT should be considered mandatory for precise anatomical localization 3
• Perform CT-based attenuation correction for accurate lesion visualization 3
• Extend imaging to include chest and neck if initial abdominal imaging is negative despite positive biochemistry 1, 2

Contrast Administration Safety

Nonionic contrast agents are safe in pheochromocytoma patients:

• The American College of Radiology confirms that nonionic contrast does not increase hypertensive crisis risk 1
• This represents a significant change from older practices that avoided contrast entirely
• Proper arterial phase assessment is essential to avoid missing small or atypically located tumors 1

Interpretation Pitfalls

Be aware of these critical diagnostic challenges:

• High-intensity adrenal uptake (more intense than liver) or inhomogeneous uptake with gland enlargement indicates abnormality 3
• Approximately 1/3 of pheochromocytomas may demonstrate washout patterns mimicking benign adenomas, creating false negatives 3
• CT-based attenuation correction can enhance physiological adrenal medulla visualization, potentially causing false-positive interpretations 4, 3
• Small pheochromocytomas or those in atypical locations may be missed without proper arterial phase imaging 1

Functional Imaging Considerations

When CT findings are negative or equivocal despite positive biochemistry:

• Consider functional imaging with 123I-MIBG scintigraphy, 18F-FDOPA PET, or 18F-FDG PET for higher sensitivity 1, 3
• FDG-PET is superior to MIBG for detecting malignant tumors, particularly in SDHB mutation carriers 1
• Functional imaging helps detect multifocal disease in biochemically confirmed cases 3

Special Cardiovascular Considerations

Patients with cardiovascular disease require meticulous perioperative management:

• Ensure thorough preoperative pharmacological preparation with alpha-blockade before any surgical intervention 4, 5
• Maintain attentive intraoperative monitoring of cardiac function, blood pressure, and fluid status 4
• Address hormonal, glucose, electrolyte, and blood pressure abnormalities as critical components of care 4

Follow-Up Imaging

Long-term surveillance is essential:

• Adrenal masses growing >5 mm/year warrant consideration for adrenalectomy after repeating functional work-up 3
• Lifelong follow-up is recommended due to risk of recurrence and metastatic disease, particularly in extra-adrenal tumors 4, 5
• Extra-adrenal pheochromocytomas have up to 40% malignancy risk and require more aggressive surveillance 5