Coronal section of the cerebral hemispheres through the midthalamus, subthalamic nucleus and midbrain. The right cerebral hemisphere shows abnormally dilated blood vessels; some of them seem to be arteries, some of them are dilated veins. These abnormal, dilated vessels occupy most of the medial portion of the right hemisphere and the tissue around this area is atrophic and pigmented. Diagnosis: Vascular malformation, most likely arteriovenous, right cerebral hemisphere.