FIG 4. 68-year-old man with history of left parietooccipital glioblastoma multiforme has new abnormal enhancement on follow-up imaging after surgery and proton beam irradiation therapy. Arrows on this postcontrast axial T1-weighted image illustrate enhancement and thickening of the septum pellucidum. Arrowhead points to involvement of the corpus callosum. Open arrow points to subependymal spread. Multiple new lesions were identified. Biopsy of a portion of the corpus callosum abnormality (arrowhead) yielded recurrent tumor.