Inclusion Criteria:

        Patients meeting the following inclusion criteria will be eligible for the study:

          -  Age ≥ 3 years of age and ≤ 21 years of age at the time of study enrollment

          -  Patients must have a pathologically proven malignant high-grade glioma (including
             glioblastoma multiforme, giant cell glioblastoma, anaplastic astrocytoma, midline
             diffuse glioma) which is progressive or recurrent despite standard care including
             surgery, radiotherapy, and/or chemotherapy

          -  Lesion must be ≥ 1.0 cm and ≤ 4.0 cm in longest dimension and surgically accessible as
             determined by MRI. Larger tumors may be surgically debulked and treated if ≤ 4.0 cm
             after debulking

          -  Multifocal disease on the unilateral side is eligible if at least one catheter can be
             placed in all multifocal areas

          -  Performance score ≥ 60% (Karnofsky for children ≥16 years old; modified Lansky for
             children < 16 years old)

          -  Patients with neurological deficits should have deficits that are stable for ≥ 1 week
             prior to enrollment. A baseline detailed neurological exam should clearly document the
             neurological status of the patient at the time of enrollment on the study

          -  Prior therapy: patients must have recovered from acute treatment related toxicities of
             all prior surgery, chemotherapy, immunotherapy, radiotherapy, differentiation therapy,
             biologic therapy, or virotherapy prior to entering this study

          -  Myelosuppressive chemotherapy: patients must have received their last dose at least 3
             weeks prior and demonstrated count recovery as defined below

          -  Investigational/Biologic agents: patients must have recovered from any acute
             toxicities potentially related to the agent and received the 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 or cellular therapy, patients must have received therapy ≥ 3 months
             prior to study entry and have recovered from all acute toxicities potentially related
             to the agent.

          -  Monoclonal antibodies: patient must have received last dose ≥ 28 days prior

          -  Radiation: Patients must have received their last fraction of radiation (≥ 54 Gy) ≥ 3
             months prior to study entry. Patients must have received local palliative radiation ≥
             28 days prior to study entry

          -  Patient must have adequate organ and marrow function as defined by the following:
             Hemoglobin ≥8 g/dL (may receive blood transfusions); absolute neutrophil count ≥ 1.0 x
             10^9 cells/L; platelet count ≥ 100 x 10^9 cells/L (transfusion independent defined as
             not receiving platelets transfusions ≥ 7 days prior to enrollment); alanine
             aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 3 times the
             institutional upper limit of normal for age; creatinine within normal institutional
             limits OR creatinine clearance > 60 mL/min/1.73 m^2 for patients with creatinine
             levels above institutional normal

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

        Exclusion Criteria:

        Patients with the following conditions will be excluded from participation in the study:

          -  Primary cerebellar, brainstem or spinal tumors

          -  Metastatic disease or gliomatosis cerebri

          -  Acute infection or medical condition precluding surgery

          -  Pregnant or lactating

          -  Diagnosis of encephalitis or central nervous system (CNS) infection < 3 months prior,
             or receiving ongoing treatment for encephalitis, CNS infection or multiple sclerosis

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

          -  Required steroid increase within 1 week prior to G207 inoculation or patients
             requiring >4 mg of dexamethasone daily

          -  Known HIV seropositivity

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

          -  Other current malignancy

          -  Concurrent anticancer or investigational drug