2018 Volume 27 Issue 8 Pages 581-588
According to a new concept for cerebrospinal fluid (CSF) dynamics, CSF is not produced mainly from the choroid plexus, and it is not absorbed from the arachnoid granule near the superior sagittal sinus, rather it is drained mainly by the lymphatic systems around the cranial nerves or lower cervical nerve root. Furthermore, CSF moves in a pulsatile fashion with blood circulation and respiration as the driving force and does not flow in one direction from the ventricle to the subarachnoid space (bulk flow theory). The CSF pulsatile movement is normally the largest around the cisterna magna and prepontine cistern. The mean total volume of intracranial CSF was ≥300 ml in the healthy controls at 70 years, <300 ml in the patients with secondary normal pressure hydrocephalus (sNPH) in which pathogenesis is thought to be due to the inflammatory adhesion in the widespread subarachnoid spaces, and ≥400 ml in the patients with idiopathic NPH (iNPH). Compared with the healthy 70-year-old controls, the patients with iNPH have about 100 ml larger ventricles and almost the same size of subarachnoid space, but the CSF distribution in the subarachnoid spaces was very different between the iNPH patients and age-matched controls. In iNPH, the Sylvian fissure and basal cistern were conspicuously enlarged, whereas the convexity part of the subarachnoid space was severely decreased. The CSF distribution in the subarachnoid space in iNPH is known to be characterized as disproportionately enlarged subarachnoid space hydrocephalus (DESH) which might be due to direct CSF communication between the lateral ventricles and the basal cistern at the inferior choroidal point of the choroidal fissure, acting as the overflow device for the ventricular drainage system. These alternative direct CSF pathways between ventricles and subarachnoid spaces other than the foramina of Luschka and Magendie have been reported. Also, the CSF distribution pattern in iNPH differed strongly from that in sNPH.
