Intracranial pressure following complete removal of a small demarcated brain tumor: a model for normal intracranial pressure in humans

Object. Current published normal values for intracranial pressure (ICP) are extrapolated from lumbar CSF pressure measurements and ICP measurements in patients treated for CSF pressure disorders. There is an-emerging agreement that true normal ICP values are needed for diagnostic and therapeutic purposes. This study documents normal ICP in humans. Methods. In this study the authors included adult patients scheduled for complete removal of a solitary, clearly demarcated, small brain tumor. The mean age of these patients was 67 years old (range 58-85 years old). Exclusion criteria were intended to create a study population with as normal brains as possible. A new telemetric ICP monitoring device was implanted at the end of surgery and monitoring was conducted 2 and 4 weeks postoperatively. Results. In the supine position, mean ICP was 0.5 +/- 4.0 mm Hg at 4 weeks postoperatively. Postural change to the standing position resulted in a decrease in mean ICP to 3.7 +/- 3.8 mm Hg. These results show ICP to be considerably lower than previously estimated. Conclusions. This study provides a preliminary reference range for normal ICP in humans. It is the first study to show that ICP in the healthy human brain decreases to negative values when assuming the upright position. If these results are later confirmed in a larger series, they might provide reference values for diagnosis and treatment in patients with CSF-related disorders. New normal values also have implications for future shunt design and the ICP target range in hydrocephalus treatment.