DISEASE CHARACTERISTICS: Patients with or without neurofibromatosis type 1 (NF1) with low grade glioma not previously treated with chemotherapy or radiotherapy Tumor types considered are: Low grade astrocytoma (Kernohan grade 1/2) Oligodendroglioma Mixed oligoastrocytoma Ganglioglioma Patients with NF1 and hypothalamic/visual pathway glioma are eligible without biopsy All CNS sites are eligible, including biopsy proven low grade spinal tumors and intrinsic brain stem tumors No malignant (anaplastic) glioma (Kernohan grade 3/4), glioblastoma multiforme, and ependymal tumors