[Note on the mechanism of producing the plateau waves]

Isotope cisternography was performed and ventricular system size was evaluated on serial computerized tomography scans in 57 patients with plateau waves in their continuous intracranial pressure recordings. The patients were assigned to three groups based on the presence or absence of communicating hydrocephalus and their intracranial pressure level: the first group comprised 23 patients with high intracranial pressure and without hydrocephalus, resulting from supratentorial brain tumor, benign intracranial hypertension and superior sagittal sinus thrombosis; the second group included 22 patients with either high intracranial pressure or communicating hydrocephalus, resulting from intracranial aneurysmal rupture: and the third group was composed of 12 patients with normal intracranial pressure and communicating hydrocephalus, resulting from intracranial aneurysmal rupture. Plateau waves in the first group patients were characterized as large plateau like formations recurring at varying intervals, with a height of 50-100 mmHg and a duration of 10 to 30 minutes. Plateau waves in the second group patients had a height of 20 to 60 mmHg and a duration of 3 to 15 minutes. The waves in the second group patients were smaller in amplitude and shorter in duration as compared with the waves in the first group patients. Plateau waves in the third group patients had an amplitude of 15 to 40 mm Hg and a duration of 3 to 10 minutes. They were the smallest in amplitude and the shortest in duration as compared with the plateau waves seen in the first and the second group patients.(ABSTRACT TRUNCATED AT 250 WORDS)