Input advanced MRI parameters to differentiate between post-radiation pseudoprogression and actual tumor recurrence.
Guidelines & Evidence
Clinical Details
Section 1
When to Use
When to Use
Evaluating new enhancing lesions 3 to 6 months following stereotactic radiosurgery (SRS) or whole-brain radiation.
Differentiating true disease progression requiring salvage surgery from self-limiting radiation death (pseudoprogression) which only requires steroids.
Section 2
Literature
Development
Standard T1 contrast MRI is notoriously blind to this distinction because both active tumors and dead irradiated brain break the blood-brain barrier, causing contrast leak. Multimodal MRI techniques (developed heavily over the 2000s) exploit the physiological differences: tumors have massive blood flow (Perfusion) and rapid cell turnover (Spectroscopy), while radiation necrosis is an avascular dead zone of lipid breakdown.
Section 3
Pearls/Pitfalls
The T1/T2 Quotient
The "T1/T2 Quotient" or mismatch tool relies on a simple observation: True metastases are highly cellular, so they are dark (isointense) on standard T2, matching the exact size of the T1 enhancement. Radiation necrosis is mostly fluid/edema, so the T2 signal is massive and blows past the borders of the T1 enhancement.
Section 4
Evidence Appraisal
Primary Reference
Radiation necrosis versus glioma recurrence: conventional MR imaging clues to diagnosis
Mullins ME et al. • AJNR Am J Neuroradiol. 2005;26(8):1967-72
