Why is non-contrast Magnetic Resonance Imaging (MRI) preferred over contrast-enhanced MRI in the surveillance of recurrent meningiomas?

Non-Contrast MRI for Surveillance of Recurrent Meningiomas

Non-contrast MRI is preferred for surveillance of recurrent meningiomas because it provides sufficient diagnostic information while avoiding unnecessary gadolinium exposure, with studies showing excellent agreement between non-contrast and contrast-enhanced sequences for monitoring tumor size and growth.

Rationale for Non-Contrast MRI in Meningioma Surveillance

• Non-contrast MRI sequences (T1, T2, FLAIR, DWI, SWI) provide valuable information about tumor cellularity, intratumoral blood products, mineralization, and the presence of CSF clefts and subjacent parenchymal edema 1
• These sequences are particularly helpful in the post-treatment surveillance context for meningiomas, allowing assessment of tumor characteristics without the risks associated with gadolinium-based contrast agents 1
• Recent research demonstrates excellent agreement between tumor size and growth measurements derived from T1 3D-gadolinium and 2D-T2WI sequences, suggesting non-contrast MRI may be appropriate for follow-up of meningiomas 2

Diagnostic Value of Non-Contrast MRI

• Non-contrast MRI has shown high sensitivity (87-93%) in identifying tumor residue or local recurrence in post-operative follow-up of brain meningiomas 3
• The sensitivity is even higher when comparing with a baseline enhanced MRI examination, regardless of magnetic field strength 3
• T2/FLAIR imaging can assist in determining extraaxial location by demonstrating a CSF cleft and can further demonstrate the presence of any subjacent parenchymal edema 1
• SWI sequences are valuable for detecting intratumoral calcifications, which are common in meningiomas 4, 5

Surveillance Protocol Based on WHO Grade

• For WHO grade 1 meningiomas, MRI surveillance is typically recommended every 6-12 months, with consideration for extending intervals after demonstrated stability 4
• More frequent surveillance is required for WHO grade 2 (atypical) and grade 3 (malignant) meningiomas 1
• For WHO grade 2 meningiomas, MRI surveillance every 3-6 months initially is recommended 4
• For WHO grade 3 meningiomas, MRI surveillance every 3 months initially is recommended 4

When Contrast Enhancement May Still Be Needed

• Contrast-enhanced MRI may be necessary in specific scenarios:
  • When evaluating for leptomeningeal metastases 1
  • When differentiating between tumor recurrence and post-treatment changes 5
  • For small residual tumors that might be missed on non-contrast imaging 3, 6
  • When tumor extension is unclear on conventional imaging 5

Limitations and Considerations

• Small residual tumors may occasionally be missed on non-contrast sequences alone 3, 6
• A baseline post-contrast MRI is valuable for future comparison with non-contrast follow-up studies 3
• Post-treatment changes can mimic tumor recurrence on conventional MRI, which may require additional advanced imaging techniques 4
• The postradiotherapy MRI should be considered the "new baseline" rather than the postsurgical MRI 4

Advanced Imaging Considerations

• MR perfusion may be useful as an adjunct tool for meningioma grading and can help detect recurrence 4
• Somatostatin receptor (SSTR) PET imaging provides superior detection sensitivity compared to contrast-enhanced MRI alone and may be useful in distinguishing tumor recurrence from post-treatment changes 5

By using non-contrast MRI for routine surveillance of recurrent meningiomas, clinicians can effectively monitor tumor status while minimizing patient exposure to gadolinium-based contrast agents, which is particularly important for patients requiring long-term follow-up.