A 3 year old boy is brought to the emergency depament after the acute onset of headache, vomiting, nuchal rigidity, and impaired mental status. MRI reveals a posterior fossa tumor that fills the 4th ventricle. Surgery is immediately staed, and intraoperative consultation leads to a "frozen section" diagnosis of medulloblastoma. Which of the following pathologic mechanisms most likely accounts for this child's clinical presentation?