The Development of Reduced Diffusion Following Bevacizumab Therapy Identifies Regions of Recurrent Disease in Patients with High-grade Glioma

Rationale and Objectives The treatment of glioma with bevacizumab results in decreased enhancement, making it challenging to diagnose tumor recurrence. Therefore, the primary aim of this retrospective study was to determine if the underlying biological processes occurring within regions of recurrent glioblastoma in patients undergoing bevacizumab therapy influence morphologic and diffusion-weighted magnetic resonance (MR) imaging characteristics. Materials and Methods In this Health Insurance Portability and Accountability Act–compliant and institutional review board–approved study, 26 patients treated with bevacizumab for high-grade glioma underwent lesion-wide apparent diffusion coefficient analysis before therapy and at the time of clinical/radiological progression, allowing for stratification by the presence or absence of reduced diffusion. Lesions with reduced diffusion were classified into “block” or “salt & pepper” phenotypes. Eight of the 26 patients underwent image-guided tissue sampling at the time of suspected disease recurrence allowing for direct biological correlation. Clinical, histologic, and MR imaging differences between diffusion groups were assessed using a two-sample Welch t test. Results All patients had histologic evidence of recurrent disease with or without a background of treatment effect. Sixty-two percent of the cohort had developed reduced diffusion at clinical progression following bevacizumab. Image-guided tissue sampling demonstrated that treatment effect was not observed within regions of reduced diffusion. Recurrent tumor intermixed with treatment effect was more likely to be observed within the “salt & pepper” phenotype when compared to “block” phenotype. Conclusions Following bevacizumab therapy, recurrent glioblastoma can manifest as nonenhancing regions characterized by reduced diffusion. Histologically, these MR imaging characteristics correlate with aggressive biological features of disease recurrence.