What is the next step in managing a cerebral pontine angle (CPA) lesion identified on contrast-enhanced computed tomography (CECT) of the brain?

Management of Cerebellopontine Angle Lesion on CECT

The next step after identifying a CPA lesion on CECT is to obtain MRI brain without and with IV contrast, which is the definitive imaging modality for characterizing these lesions and guiding treatment planning. 1

Why MRI is Essential

CECT has significant limitations for CPA lesions and should be considered only a screening tool 1:

• MRI provides superior soft tissue resolution necessary to differentiate between the various CPA pathologies 2
• Contrast-enhanced MRI is critical for surgical and radiation treatment planning due to excellent tissue characterization 1
• CT may miss up to 25% of small pontine/CPA lesions initially 3, 4

Specific MRI Protocol Recommendations

The optimal MRI study should include 1:

• 3D heavily T2-weighted sequences (particularly useful for identifying vascular loops and characterizing cisternal anatomy) 1
• High-resolution 3D T1 pre- and post-contrast imaging 1
• Axial T2 FLAIR sequences 1
• Diffusion-weighted imaging (DWI) 1

Differential Diagnosis by Location

For CPA lesions specifically, the primary diagnostic considerations are 1:

1. Schwannoma (most common, typically acoustic neuroma)
2. Meningioma (second most common)
3. Metastasis
4. Choroid plexus tumors 1
5. Exophytic brainstem tumors (gliomas, ependymomas) 5

Critical Imaging Features to Assess on MRI

When reviewing the MRI, specifically evaluate 6, 5:

• Site of origin (extraaxial vs. intraaxial) - this is the most important factor for diagnosis 6
• Margin characteristics - blurring between tumor and brainstem suggests intraaxial origin 5
• Internal auditory canal involvement - extension into IAC strongly suggests schwannoma 5
• Enhancement pattern - helps differentiate tumor types 6
• Peritumoral T2 hyperintensity - disproportionate edema suggests intraaxial origin 5
• Fourth ventricle lateral recess dilation - may indicate exophytic intraaxial tumor 5

Additional Considerations

For hypervascular lesions (hemangioblastoma, hemangiopericytoma, paraganglioma), pre-surgical angiography may be warranted both diagnostically and therapeutically for embolization 7

Assess cranial nerve function clinically, particularly nerves V-VIII which traverse this region, as this helps narrow the differential diagnosis 1, 3

Consider spine imaging if there is concern for neurofibromatosis type 2 (multiple schwannomas) or leptomeningeal spread 1