Glioblastoma Butterfly Corpus Callosum

A 62-year-old right-handed architect presents with 6 weeks of progressive morning headache, projectile vomiting, and personality change. Over the last 2 weeks he has developed left-hand clumsiness, urinary incontinence, and a new-onset focal seizure. MRI shows a large heterogeneous ring-enhancing mass centered on the corpus callosum extending symmetrically into both frontal lobes. Stereotactic biopsy and maximal safe debulking are performed. The gross pathology specimen shown as **B** demonstrates a large poorly demarcated tumor straddling the corpus callosum with a variegated appearance. Which of the following best describes the characteristic gross pathological features of the structure marked **B**?