The Role of Cerebrospinal Fluid Dynamics in Normal Pressure Hydrocephalus Diagnosis and Shunt Prognostication

Over the years, there have been several reports and trials of the resistance to cerebrospinal fluid (CSF) outflow (Rout) in normal pressure hydrocephalus (NPH). This work aimed to revisit the utility of testing CSF circulation in a large population of patients clinically presenting with NPH.

We retrospectively analyzed the data of 369 NPH patients-either shunted or with endoscopic third ventriculostomy (ETV)-in Cambridge between 1992 and 2018. We determined the patients' outcomes (improvement versus no improvement at 6 months) by applying a threshold on R _out values and compared our results with those of existing literature. We also conducted a correlation analysis between all variables and calculated Chi-Statistics (as a measure of separability between improvement and no improvement outcomes) to determine a subset of variables which achieved the highest accuracy in prediction of outcome.

In our dataset, R _out of 18 mmHg*min/mL achieved the highest Chi-statistics of 9.7 with p-value <0.01 when adjusted for age. In addition to R _out, intracranial pressure (ICP) values at the baseline and plateau, CSF production rate and ICP amplitude to slope ratio showed significant Chi-Statistics values (more than 5). Using these variables, an overall accuracy of 0.70 ± 0.09 was achieved for prediction of the shunt outcome.

Rout can be used for selecting patients for shunt surgery but not for excluding patients from treatment. Critical, multivariable approaches are required to comprehend CSF dynamics and pressure-volume compensation in NPH. Outcome definition and assessment could also be brought to question.