Larger hippocampal and brainstem volumes in high volume lumbar puncture responders as a predictor of shunt response in normal pressure hydrocephalus

Background Normal pressure hydrocephalus (NPH) is a treatable cause of dementia, urinary incontinence and gait abnormality which is important to diagnose early as the longer the delay in treatment, the worse the outcome after shunting. Gait improvement following high volume lumbar puncture (HVLP) and continuous lumbar drain (cLD) is widely used to predict shunt responsiveness in patients with suspected NPH. Here, we investigate differences in MRI volumetric and traditional measures between HVLP/cLD responders and non‐responders to identify imaging features that may help predict shunt response. Method 82 patients with suspected NPH were studied retrospectively. Gait testing was performed before and immediately/24‐hours/72‐hours after CSF removal. A positive response to HVLP/cLD was defined as improvement in gait following the procedure. The 36 responders (26 men; mean‐age 79.3±6.3) and 46 non‐responders (25 men; mean‐age 77.2±6.1) underwent pre‐procedure 3T brain MRI including 3D‐MPRAGE sequence. 66 subcortical regional volumes were segmented using FreeSurfer. After normalizing for total intracranial volume, two‐tailed student's t‐test and chi‐square test were used to characterize statistical group‐differences. Assessment of Evan’s‐index (EI), callosal‐angle (CA) and disproportionately enlarged subarachnoid space hydrocephalus (DESH) were also made. Multivariable logistic regression models were tested using Akaike information criterion to determine which combination of metrics is most accurate in prediction of HVLP/cLD response. Result Responders and non‐responders demonstrated no differences in total ventricular and white/gray matter volumes and in EI and DESH. CA (in men) and third and fourth ventricular volumes were decreased; and hippocampal and brainstem volumes were increased in responders (p