Mechanical instability as a signature of viscoelastic decoupling at the tumor-brain interface.

Brain tumors alter the viscoelastic equilibrium of surrounding tissue, but how these changes shape the mechanics of tumor-brain coupling remains unclear. This study introduces mechanical instability mapping, a voxelwise measure of imbalance between elastic storage and viscous dissipation derived from magnetic resonance elastography (MRE). Twenty-eight patients (15 meningiomas, 13 glioblastomas) were analyzed using standardized 3 T MRE and tumor segmentation. Quantitative descriptors of instability topology-including skeleton length and branch-point densities, and radial persistence (radial-AUC)-were compared across WHO I, WHO II, and glioblastoma groups. Glioblastomas showed diffuse, branched instability fields with significantly higher skeleton and branch-point densities and lower radial-AUC compared with WHO I meningiomas, which exhibited compact, radially coherent patterns. Group-average probability maps indicated a transition from coherent to fragmented instability with increasing malignancy. These findings demonstrate that peritumoral mechanical topology reflects the degree of viscoelastic coupling at the tumor-brain interface. Instability mapping thereby extends conventional stiffness-based MRE metrics, offering a quantitative framework for assessing interface integrity and heterogeneity that may aid in elasticity-guided treatment strategies and biomechanical phenotyping of brain tumors.