Also known as stereotaxic surgery; guided brain surgery. Stereotactic surgery is performed through a tiny hole in the skull and guided by CT (computed tomography) scanning. This procedure may be performed in people with advanced Parkinson disease (a progressive, degenerative disease of the nervous system characterized by muscle rigidity, weakness, and tremor), for whom medications are no longer effective. It can also be used to remove deep brain tumors or abscesses.