Astrocytomas are the most common type of childhood glioma -- a type of central nervous tumor Like all gliomas, astrocytomas consist of glial cells, which form the connective tissue of the brain. Astrocytomas can occur in both the brain and spine, but most often occur in the cerebellum (the part of the brain that coordinates movement and balance), optic nerve and in the brainstem. Astrocytomas can be benign or malignant.