Ventricular size and isotope cisternography in patients with acute transient rises of intracranial pressure (plateau waves)

Abstract

The size of the ventricular system and cerebrospinal fluid (CSF) flow were determined in 17 patients with plateau waves, using computerized tomography (CT) and isotope cisternography. Some patients had increased intracranial pressure (ICP) resulting from space-occupying lesions and other causes, and some had normal ICP observed in normal-pressure hydrocephalus. The size and shape of the ventricular system during plateau wave phases as ascertained by CT showed little or no change as compared with its size and shape during the interval phases between two waves. It was also noticed that, in patients with supratentorial masses, the midline shift showed no difference in degree between the two phases. These findings suggest that there is little change in the intracranial CSF volume between the two phases, that is, there is little compensatory outflow of the intracranial CSF for the ICP variations. These results may also support the assumption that the plateau waves are not caused by an intermittent obstruction of the CSF pathways. Isotope cisternography showed a marked delay of clearance of radioactivity from the intracranial CSF in 15 patients. The cisternographic pattern in patients with increased ICP and the absence of ventricular dilatation demonstrated an abnormally large accumulation of radioactivity over the cerebral convexities, and the pattern in patients with normal-pressure hydrocephalus showed complete obstruction of the subarachnoid space over both cerebral convexities. These observations suggest that, in patients with plateau waves, there is a marked delay in CSF absorption. The authors postulate that the reduction of CSF absorption may create a critically tight condition within the cranial cavity and act as a contributory factor in the development of the plateau waves.