Best CT Phase for Visualizing Pheochromocytoma
The arterial phase is the optimal CT phase for visualizing pheochromocytoma, with arterial phase enhancement values above 110 HU strongly suggesting pheochromocytoma over other adrenal masses. 1
Imaging Characteristics of Pheochromocytoma
- Pheochromocytomas demonstrate significantly higher enhancement in the arterial phase compared to adrenal adenomas, with mean arterial enhancement of 104 HU for pheochromocytomas versus 37 HU for adenomas 2
- Most pheochromocytomas (58%) appear heterogeneous on CT imaging, compared to only 22% of adenomas 2
- In a recent study, arterial phase attenuation provided high discriminatory value with 100% sensitivity at 87.6 HU and 100% specificity at 139.9 HU for distinguishing pheochromocytomas from adenomas 1
CT Protocol Recommendations
A complete CT protocol for evaluating suspected pheochromocytoma should include:
- Unenhanced phase (to assess for baseline density)
- Bolus-tracked arterial phase (critical for pheochromocytoma detection)
- Venous phase (45 seconds post-arterial)
- Delayed phase (15 minutes post-arterial) 1
Venous phase enhancement ≥85 HU has a sensitivity of 88.2% and specificity of 83.7% for diagnosing pheochromocytoma versus adenoma 3
Safety Considerations
- While MRI has traditionally been preferred for suspected pheochromocytoma due to theoretical risk of hypertensive crisis with IV contrast for CT, modern nonionic contrast agents appear safe 4, 5
- A retrospective study of 25 patients with 40 pathologically proven pheochromocytomas or paragangliomas who received nonionic IV contrast material for CT found no adverse events, even without alpha-blocking medication 5
Important Diagnostic Pitfalls
- Relying solely on washout characteristics can lead to misdiagnosis, as a significant subset of pheochromocytomas (66.7%) may demonstrate washout patterns mimicking lipid-poor adenomas 3
- Arterial phase enhancement should be evaluated alongside washout calculations to avoid potential misdiagnosis 3
- Small pheochromocytomas or those in atypical locations may be missed on conventional CT imaging without proper arterial phase assessment 6
Additional Imaging Considerations
- For biochemically confirmed pheochromocytoma with negative initial CT imaging, consider extending imaging to include chest and neck 6
- Functional imaging with 123I-MIBG scintigraphy, 18F-FDOPA PET, or 18F-FDG PET provides higher sensitivity for detecting small or atypically located tumors 6
- In patients with established pheochromocytoma, FDG-PET appears superior to MIBG for detecting malignant tumors, particularly in patients with SDHB mutation 4