Figure 29-1. Schematic representation of the bulk flow of CSF from the lateral ventricles, through the third and fourth ventricles, outward from the basal foramina (Luschka and Magendie), upward around the brainstem and basal cisterns to both the convexities of the hemispheres and downward to spinal subarachnoid space. Most absorption is presumed to occur over the cerebral convexities, abutting the sagittal sinus.
Figure 29-2. Schematic depiction of Lundberg waves that are seen with recordings of intracranial pressure. The A-waves (plateau waves) are appreciated only on trend recordings of pressure and consist of spontaneous or induced elevations of pressure to 25 to 50 mm Hg that begin over less than a minute and persist for many minutes before declining to baseline values. B-waves are ballistic deflections that reflect entry of blood into the main basal arteries and conductance vessels of the brain during cardiac systole. The insert shows the dicrotic and reflected “notches” within a B-wave, (P1, P2, and P3 not all of which are always visible); an increase in P2 amplitude above P1 is indicative or reduced intracranial compliance.
Figure 29-3. MRI of adult tension hydrocephalus from a congenital stenosis of the cerebral aqueduct. There is transependymal movement of water that appears as a T2 signal in a rim surrounding the lateral ventricles. The third ventricle, but not the fourth, is enlarged.
Figure 29-4. CT of a patient with normal-pressure hydrocephalus. There is enlargement of all the ventricles, particularly of the frontal horns of the lateral ventricles (left), which is roughly disproportionate to the cortical atrophy (right). The frontal horn span is over 39 mm. Various formulas have been devised to quantitate the imaging features, but they are difficult to apply.
Figure 29-5. Fluid-attenuated inversion recovery (FLAIR) MRI sequence in a patient man with hydrocephalus, shunt failure, and L-dopa-responsive parkinsonism. There is signal change in the dorsal midbrain and periaqueductal region.
Figure 29-6. MRI after gadolinium infusion (T1 sequence) showing the widespread dural enhancement that is typical of low CSF pressure after lumbar puncture, spontaneous CSF leakage, or shunt overdrainage. Similar changes may be found in the spinal dura.
Figure 29-7. MRI with gadolinium infusion showing diffuse rheumatoid pachymeningitis in an older man with minimal systemic disease. He had severe headaches, hydrocephalus, and mental dullness.
Chapter  29    Disturbances of CSF and Its Circulation
Tumors of the central nervous system constitute a vitally important chapter of neurologic medicine. Their importance derives from their great variety; the numerous neurologic symptoms caused by their size, location, and invasive qualities; the destruction and displacement of tissues in which they are situated; the elevation of intracranial pressure they cause; and, most of all, their lethality. The nature of practice for brain tumors is changing as a result of advances in anesthesiology, stereotactic and microneurosurgical techniques, focused radiation therapy, and the use of new chemotherapeutic agents. Moreover, our understanding of the genetic aspects of brain tumors is undergoing vast changes, which offer the prospect of new treatments.