Methotrexate Infusion Into Fourth Ventricle in Children With Recurrent Malignant Fourth Ventricular Brain Tumors

The goal of this clinical research study is to establish the maximum tolerated dose (MTD) of direct administration of methotrexate into the fourth ventricle of the brain in patients with recurrent malignant brain tumors including medulloblastoma, primitive neuroectodermal tumors (PNET), atypical teratoid/rhabdoid tumors (AT/RT), and ependymoma. Methotrexate is designed to block cancer cells from dividing, which may slow or stop their growth and spread throughout the body. This may cause the cancer cells to die.