The importance of CSF distribution for target values and risk profiling for idiopathic Normal Pressure Hydrocephalus shunt surgery

BACKGROUND AND PURPOSE: Idiopathic Normal Pressure Hydrocephalus is characterized by gait disturbance, cognitive impairment, and urinary incontinence. Symptom improvement can be achieved by shunt surgery, especially regarding gait difficulties. This study investigated whether CSF volumetry can define postoperative target values associated with clinical improvement and, secondly, predict potential non-response or overdrainage complications. MATERIALS AND METHODS: Forty-seven patients with iNPH were prospectively followed for three years after shunt surgery. Quantitative MRI was performed at baseline and at 3, 12, and 36 months postoperatively. Automatic segmentation yielded ventricular volume, subarachnoid CSF volume, ratio of ventricular and total CSF volume and ratio of total brain volume and intracranial volume. Clinical outcome was assessed using the Hellström iNPH scale. Patients were classified as responders and non-responders and further subdivided with and without overdrainage complications. RESULTS: Eighty-seven percent of patients were classified as responders. Responders demonstrated a 26% reduction in ventricular volume(139 ml at baseline and 102 ml at three years) accompanied by a >60% improvement in iNPH score. The ventricular/total CSF ratio decreased from 0.34 to 0.25. Non-responders exhibited low ratios already at baseline, due to a significantly higher subarachnoid CSF volume. Overdrainage-related postural headaches were associated withlow subarachnoid CSF volume, younger age, higher baseline iNPH score, and higher BPV/ICV ratio. Aggregate z-scores combining multiple baseline metrics improved discrimination between responders, non-responders, and patients at risk for overdrainage. CONCLUSIONS: Baseline volumetry may provide target values and risk stratification for shunt surgery in iNPH. Responders showed a reduction of ventricular volume to ∼100 ml and ventricle/total CSF ratio to ∼0.25. High subarachnoid CSF volumes at baseline, however, was associated with poor response, while low subarachnoid CSF volume indicated an increased risk of postural headache. Quantitative CSF segmentation may improve patient selection and postoperative management in iNPH.