Inclusion Criteria:

          -  Age ≥ 36 months and < 19 years

          -  Pathologically proven malignant cerebellar brain tumor (including medulloblastoma,
             glioblastoma multiforme, giant cell glioblastoma, anaplastic astrocytoma, primitive
             neuroectodermal tumor, ependymoma, atypical teratoid/rhabdoid tumor, germ cell tumor,
             or other high-grade malignant tumor) which is progressive or recurrent despite
             standard care including surgery, radiotherapy, and/or chemotherapy. A pathologically
             proven secondary malignant cerebellar tumor without curative treatment options is
             eligible.

          -  Lesion must be ≥ 1.0 cm ≤ 3.0 cm in diameter and surgically accessible as determined
             by MRI. Larger tumors may be surgically debulked and treated if ≤ 3.0 cm after
             debulking

          -  Patients must have fully recovered from acute treatment related toxicities of all
             prior chemotherapy, immunotherapy or radiotherapy prior to entering this study.

          -  Myelosuppressive chemotherapy: patients must have received their last dose at least 3
             weeks prior (or at least 6 weeks if nitrosurea)

          -  Investigational/Biologic agents: patients must have recovered from any acute
             toxicities potentially related to the agent and received last dose ≥ 7 days prior to
             entering this study (this period must be extended beyond the time during which adverse
             events are known to occur for agents with known adverse events ≥ 7 days). For viral
             therapy, patients must have received viral therapy ≥ 3 months prior to study entry and
             have recovered from all acute toxicities potentially related to the agent.

          -  Monoclonal antibodies: The patient must have received last dose ≥ 21 days prior.

          -  Radiation: Patients must have received their last fraction of craniospinal radiation
             (>24 Gy) or total body irradiation ≥ 3 months prior to study entry. Patients must have
             received focal radiation to symptomatic metastatic sites or local palliative radiation
             ≥ 28 days prior to study entry.

          -  Autologous bone marrow transplant: Patients must be ≥ 3 months since transplant prior
             to study entry.

          -  Normal hematological, renal and liver function (absolute neutrophil count > 1000/mm3,
             platelets > 100,000/mm3, prothrombin time (PT) or partial thromboplastin time (PTT) <
             1.3 x control, creatinine within normal institutional limits OR creatinine clearance
             >60 mL/min/1.73 m2 for patients with creatinine levels above institutional normal,
             total bilirubin < 1.5 mg/dl, transaminases < 3 times above the upper limits of the
             institutional norm)

          -  Patients < 16 years, Modified Lansky performance score ≥ 60; patients ≥ 16 years,
             Karnofsky performance score ≥ 60

          -  Patient life expectancy must be at least 8 weeks

          -  Written informed consent in accordance with institutional and FDA guidelines must be
             obtained from patient or legal guardian

        Exclusion Criteria:

          -  Any treatment outside the allowable guidelines outlined in section 5.1.

          -  Acute infection, granulocytopenia or medical condition precluding surgery

          -  Pregnant or lactating females

          -  Prior history of encephalitis, multiple sclerosis, or other central nervous system
             infection

          -  Tumor involvement which would require ventricular or brainstem inoculation or would
             require access through a ventricle in order to deliver treatment

          -  Required steroid increase within 1 week prior to injection

          -  Known HIV seropositivity

          -  Concurrent therapy with any drug active against HSV (acyclovir, valacyclovir,
             penciclovir, famciclovir, gancyclovir, foscarnet, cidofovir) or any immunosuppressive
             drug therapy (except dexamethasone or prednisone).