RATIONALE: Drugs used in chemotherapy, such as methotrexate, cyclophosphamide, etoposide phosphate, dexamethasone, and cytarabine, work in different ways to stop cancer cells from dividing so they stop growing or die. Osmotic blood-brain barrier disruption uses certain drugs to open the blood vessels around the brain and allow anticancer substances to be delivered directly to the brain. Giving methotrexate, cyclophosphamide, and etoposide phosphate with osmotic blood-brain barrier disruption plus dexamethasone and cytarabine may kill more cancer cells.