Comparison of elevated intracranial pressure pulse amplitude and disproportionately enlarged subarachnoid space (DESH) for prediction of surgical results in suspected idiopathic normal pressure hydrocephalus

Background: To compare the prognostic value of pulse amplitude on intracranial pressure (ICP) monitoring and disproportionately enlarged subarachnoid space hydrocephalus (DESH) on magnetic resonance imaging (MRI) for predicting surgical benefit after shunt placement in idiopathic normal pressure hydrocephalus (iNPH).

Method: Patients with suspected iNPH were prospectively recruited from a single centre. All patients received preoperative MRI and ICP monitoring. Patients were classified as shunt responders if they had an improvement of one point or more on the NPH score at 1 year post-surgery. The sensitivity, specificity, Youden index, and positive and negative predictive values of the two diagnostic methods were calculated.

Results: Sixty-four of 89 patients clinically improved at 1 year post-surgery and were classed as shunt responders. Positive DESH findings had a sensitivity of 79.4 % and specificity of 80.8 % for predicting shunt responders. Fifty-five of 89 patients had positive DESH findings: 50 of these responded to VP shunt, giving a positive and negative predictive value of 90.9 % and 61.8 %, respectively. Fifty-seven of 89 patients had high ICP pulse amplitude. High ICP pulse amplitude had a sensitivity of 84.4 %, specificity of 88 %, positive predictive value of 94.7 % and negative predictive value of 61.8 % for predicting shunt responders.

Conclusions: Both positive DESH findings and high ICP pulse amplitude support the diagnosis of iNPH and provide additional diagnostic value for predicting shunt-responsive patients; however, high ICP amplitude was more accurate than positive DESH findings, although it is an invasive test.