A 7-year-old, M/N, Boxer dog is presented for evaluation of an acute onset of cluster seizures. Neurologic examination between events reveals an altered mental status with a left-sided menace response deficit but normal vision (verified by tracking). Fundic examination is unremarkable. MRI of the brain reveals a poorly demarcated, T2-hyperintense, contrast-enhancing mass in the right parietal/piriform lobe that crosses the midline at the level of the corpus callosum. CSF analysis is unremarkable. Which is the MOST likely diagnosis?