PLATEAU-WAVE PHENOMENON .2. OCCURRENCE OF BRAIN HERNIATION IN PATIENTS WITH AND WITHOUT PLATEAU WAVES

From 1980 to 1989, during intracranial pressure (ICP) recording, brain herniation (central transtentorial herniation associated with uncal herniation) developed in 15 patients as a result of aneurysmal rebleeding, uncontrollable brain swelling and/or oedema in spite of attempts at treating increased ICP. The relationship between the ICP level at which herniation occurred and the ICP fluctuation patterns in continuous ICP recordings prior to the development of the herniation was studied retrospectively. As for the ICP fluctuation patterns, the patients were assigned to 2 groups on the basis of the presence or absence of plateau waves of Lundberg: group I comprising 8 patients without plateau waves but with a high ICP, and group II comprising 7 patients with both plateau waves and a high ICP. In the group I patients the herniation occurred as a result of aneurysmal rebleeding or brain swelling after subarachnoid haemorrhage, and in the group II patients the herniation resulted from brain tumour, meningitis carcinomatosa and superior sagittal sinus thrombosis. In the group I patients the herniation developed at a mean ICP level of 70-98 mmHg, and in the group II patients it occurred at a mean ICP level of 120-150 mmHg, far higher than the ICP level causing herniation in the group I patients. It has been shown that patients with a plateau-wave phenomenon in continuous ICP recordings have a marked impairment of cerebrospinal fluid (CSF) absorption and a delayed CSF flow. We suggest that the group II patients have an impairment of CSF absorption and a markedly sluggish CSF flow, and this condition produces a large accumulation of CSF either in the cranial or in the spinal canal cavities, creating a critically taut condition in which pressure gradients can no longer be permitted within these cavities, and which act as a defence mechanism against the herniation, despite the marked increase in the ICP.