Predicting Pseudoprogression and Progression in Vestibular Schwannoma After Radiosurgery Using Dynamic GRASP MRI

Introduction: Pseudoprogression, transient volumetric increase, can be commonly observed in vestibular schwannomas after radiosurgery, and may be explained by inflammation, necrosis, and scarring. A clinical biomarker would be valuable for pseudoprogression as it can occur even years after radiosurgery. Golden-angle radial sparse parallel (GRASP) dynamic contrast-enhanced MRI measures how fast contrast enters and exits the tumor. Our hypothesis is that fast contrast entry on GRASP MRI is more consistent with tumor and slow entry with scar tissue.

Methods: We calculated the tumor peak, wash-in and washout slopes, normalized to the superior sagittal sinus, from longitudinal GRASP images obtained from twenty patients with vestibular schwannomas. Six cases were categorized as progression, seven pseudoprogression and seven response after radiosurgery at NYU. Comparisons were made to the images prior to volume increase in the case of pseudoprogression/progression, or to the pre-radiosurgery images otherwise.

Results: The wash-in slope was significantly reduced over time (p = 0.02) with pseudoprogression but not in cases of progression (p = 0.31). The appearance of intra-tumoral necrosis was correlated with pseudoprogression as opposed to progression (p = 0.001). The absolute washout slope was reduced over time with pseudoprogression (p = 0.02), and increased in cases of progression (p = 0.03). Pseudoprogression and regressed tumors had similar longitudinal changes in contrast washout profile, while progressed tumors demonstrated a significant relative increase in slope (p = 0.005). The absolute and relative changes in washout parameter differentiated cases of progression and pseudoprogression with AUC of 1.00 (95% confidence interval, 1.00-1.00).

Conclusion : The changes in washout slope is keeping with our hypothesis of faster dynamics demonstrated by tumor growth. Our study show GRASP is a promising imaging biomarker to assess tissue characteristics and help differentiate vestibular schwannoma progression from pseudoprogression after radiosurgery. Further studies will validate this approach.