What imaging modalities are recommended for localizing a suspected pheochromocytoma?

Pheochromocytoma Imaging

Start with contrast-enhanced CT of the abdomen and pelvis as your first-line anatomical imaging modality once biochemical diagnosis is confirmed. 1

Initial Imaging Approach

Anatomical Imaging (First-Line)

CT with contrast is the preferred initial imaging study for localizing pheochromocytomas and paragangliomas (PPGLs), offering excellent spatial resolution with sensitivity between 88-100% for detecting these tumors. 1 Modern CT can detect tumors as small as 5 mm, and because most PPGLs are located in the abdomen, CT of the abdomen and pelvis should be your starting point.

Important safety note: Nonionic contrast is safe and can be administered without prior adrenergic receptor blockade—you do not need to wait for alpha-blockade before performing contrast CT. 1

When to Use MRI Instead

Switch to MRI as your primary anatomical imaging in these specific situations: 1

• Metastatic disease (MRI superior for extra-adrenal, residual, or recurrent tumors)
• Head and neck paragangliomas (MRI sensitivity 90-95%)
• Patients with surgical clips causing CT artifacts
• CT contrast allergy
• Radiation exposure concerns: children, pregnant women, known germline mutation carriers, or recent excessive radiation exposure

Avoid ultrasound—it has suboptimal sensitivity and is not recommended. 1

Functional Imaging: When and What to Use

For Sporadic, Non-Metastatic Pheochromocytoma

123I-MIBG scintigraphy is sufficient for confirming diagnosis and ruling out extraadrenal disease in apparently sporadic cases. 2 It has comparable sensitivity to PET imaging (81-88%) and provides whole-body screening capability. Reserve PET tracers for:

• MIBG-negative cases
• Multifocal tumors on MIBG
• Patients on medications interfering with MIBG accuracy

For Paragangliomas (Extra-Adrenal)

18F-FDOPA PET is the most sensitive functional imaging modality for paragangliomas, with higher sensitivity than 123I-MIBG and greater specificity than 18F-FDG PET. 2

For head and neck paragangliomas specifically: 18F-FDOPA PET approaches 100% sensitivity. 2 If unavailable, use somatostatin receptor scintigraphy with 111In-pentetreotide SPECT/CT or 68Ga-DOTATATE PET as alternatives.

For Metastatic Disease

Your imaging strategy must be genotype-driven: 2, 3

• SDHB-related metastatic disease: Use 18F-FDG PET (sensitivity 83% per lesion in SDHB-positive patients) or 18F-FDA PET
• Non-SDHB metastatic disease or unknown genotype: Use 18F-FDOPA PET or 18F-FDA PET
• 18F-FDA PET has the highest sensitivity and specificity across all genetic subtypes but suffers from limited availability 2, 3

Critical pitfall: 123I-MIBG scintigraphy alone significantly underestimates metastatic disease burden and can lead to inappropriate management decisions. 2

For MEN2-Related Pheochromocytoma

18F-FDOPA PET is preferred over 123I-MIBG (which has suboptimal sensitivity/specificity in MEN2) and 18F-FDG PET (only 40% sensitive in MEN2). 2 The absence of physiologic 18F-FDOPA uptake in normal adrenal glands makes it particularly useful for MEN2 staging and restaging.

Practical Algorithm

1. Confirm biochemical diagnosis first—never start imaging without clear biochemical evidence 1

2. Perform contrast-enhanced CT abdomen/pelvis (or MRI if contraindications exist)

3. Add functional imaging based on clinical scenario:

   • Sporadic adrenal: 123I-MIBG sufficient
   • Extra-adrenal/paraganglioma: 18F-FDOPA PET preferred
   • Metastatic SDHB: 18F-FDG PET
   • Metastatic non-SDHB: 18F-FDOPA PET
   • Head/neck: 18F-FDOPA PET (nearly 100% sensitive)

4. Consider genetic testing to guide functional imaging selection and long-term surveillance 4, 5

Common Pitfalls to Avoid

• Don't delay contrast CT for alpha-blockade—nonionic contrast is safe without pretreatment 1
• Don't rely solely on 123I-MIBG for metastatic disease—it misses significant disease burden 2
• Don't use 18F-FDG PET in MEN2 patients—sensitivity is only 40% 2
• Don't forget that CT is preferred over MRI for detecting lung metastases 1
• Remember that 50% of normal adrenal glands show physiologic 123I-MIBG uptake, potentially causing false-positives 1