Diffusion restriction in a non-enhancing metastatic brain tumor treated with bevacizumab - recurrent tumor or atypical necrosis?

A 38-year-old female with metastatic brain cancer developed non-enhancing, diffusion restricted lesions following bevacizumab treatment. From our review of the literature, this is the first reported case of this type of lesion. Clinicians should be wary of these lesions, as they can represent either tumor progression or necrosis/effects of chronic hypoxia from anti-angiogenic therapy. Further investigation is necessary to determine the biological mechanism and clinical significance of this type of imaging appearance.