The CSF Pulse Wave in Hydrocephalus
This was a letter to the editor in response to comments by C. Di Rocco criticizing the paper “The CSF pulse wave in hydrocephalus” (Child’s Nerv Syst 1:248–254). Di Rocco did not agree with our comment that the CSF pressure pulse emanates from the cerebral venous bed but rather is “significant only in conditions of increased return of venous blood to the heart.” Our studies indicate that 1) the pulse is not transmitted from the heart in a retrograde manner because obstruction of the transverse sinuses in dogs with diversion of the venous outflow failed to obliterate the sagittal sinus pulse. 2) the pulse wave measured in the CSF and in the cerebral veins are identical. Thus, the pulse originates in the veins and is transmitted to the CSF, or vice versa. If the pulse originates in the CSF, it must come from some vascular structure in contact with the CSF. The usual explanation is that the pulse originates in the arteries at the base of the brain and is modified by ‘compliance’ of the system with the pulse impressed upon the cerebral veins acting as a tambour. CSF and venous pulse waves were measured in our laboratory so as to eliminate the tambour effect. The pulse waves were still identical. We are left with the conclusion that the venous pulse is an antegrade phenomena and is transmitted from the veins to the CSF. As regards asymmetric ventricles in a shunted patient, the pressure gradient is not between the ventricles. The gradient is between the intracranial contents and the distal end of the shunt. This causes CSF and the viscoelastic brain to flow toward the ventricular catheter. The tendency to flow is more dispersed the further the ventricular surface is from the pressure sink, Le., the ventricular catheter. Thus the ventricle with the catheter is the smaller ventricle.