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. • Introduces mechanical instability mapping as a quantitative framework to characterize tumor–brain interaction from in vivo magnetic resonance elastography. • Demonstrates that instability topology distinguishes benign from malignant intracranial tumors, separating elastically coupled meningiomas from mechanically decoupled glioblastomas. • Reveals fragmented, dissipative peritumoral instability fields as a biomechanical signature of invasive tumor growth. • Establishes instability topology as a mechanistic link between imaging, histopathology, and operative behavior, with implications for elasticity-guided neurosurgery and MR-based histopathology.