A 58-year-old man presents with a 3-week history of progressive morning headaches and recent-onset seizures. MRI brain reveals a large heterogeneous mass with the characteristic "butterfly" appearance crossing the midline. The structure marked **A** in the diagram represents the tumor crossing the corpus callosum and involving both cerebral hemispheres. Which of the following histopathological features would be MOST characteristic of this lesion and support the diagnosis of glioblastoma (IDH-wildtype, WHO Grade 4)?