This exhibit features four illustrations of the brain comparing normal brain anatomy with the effects of a cystic cerebellar tumor. The normal circulation of CSF begins with its production by modified ependymal cells in the choroid plexus, around blood vessels, and along ventricular walls. CSF then circulates into the lateral ventricles, third ventricle, fourth ventricle, median aperture, lateral apertures, into the subarachnoid space around the spinal cord and brain. The presence of a cystic cerebellar tumor compresses the midbrain and cerebellum. The cerebral aqueduct is compressed, stopping the circulation of CSF and causing it to collect in the ventricles. The pressure within the ventricles increases, causing the CSF to migrate into the brain tissue. Brain tissue then swells with fluid, restricting blood supply to the brain. This results in oxygen deprivation and more swelling.