ICP and CBF regulation: effect of the decompressive craniectomy

The view of the intracranial system as a rigid and closed box has been criticised by many authors who take into account the possibility of a certain degree of elastic bulk accommodation, mainly in the spinal sac. In nine patients, who underwent decompressive craniectomy for treatment of life-threatening intracranial hypertension, when the clinical conditions improved, just before cranioplasty, the blood flow velocities at middle cerebral artery (MCA) and at superior sagittal sinus (SSS) level were simultaneously recorded. The measurements were repeated after cranioplasty. The blood flow velocity recorded from SSS in craniectomized patients appeared flat, without evident pulsation; after cranioplasty a clear-cut pulsatile wave became again evident. The disappearance of a pulsatile shape in the blood flow velocity recorded from the SSS when the intracranial system was "open" and the reappearance of a pulsatile blood flow waveform after the "closure" of the skull confirm that the venous bed acts as a bulk compensatory system in order to maintain the intracranial volume absolutely constant.