Decreases in ventricular volume correlate with decreases in ventricular pressure in idiopathic normal pressure hydrocephalus patients who experienced clinical improvement after implantation with adjustable valve shunts

Abstract

Objective: This retrospective study examined whether changes in ventricular volume correspond with changes in adjustable valve pressure settings in a cohort of patients who received shunts to treat idiopathic normal pressure hydrocephalus. We also examined whether these pressure-volume curves and other patient variables would co-occur with a positive clinical response to shunting.

Methods: We selected 51 patients diagnosed with idiopathic normal pressure hydrocephalus who had undergone implantation of a Codman Hakim programmable valve (Medos S.A., Le Locle, Switzerland). Clinical data were gathered from the patients' records and clinical notes by an investigator blinded to patients' ventricular volumes. Ventricular volume was measured using 3D Slicer, an image analysis and interactive visualization software package developed and maintained at the Surgical Planning Laboratory at Brigham and Women's Hospital.

Results: Eighty-six percent of patients with gait disturbance at presentation showed improvement of this symptom, 70% experienced improvement in incontinence, and 69% experienced improvement in dementia. For the group showing 100% clinical improvement, the correlation coefficient of average changes in valve pressure over time (delta P/delta T) and average changes in ventricular volume over time (delta V/delta T) were high at 0.843 (P < 0.05). For the group experiencing no or only partial improvement, the correlation coefficient was 0.257 (P = 0.32), indicating no correlation between average delta V/delta T and average delta P/delta T for each patient.

Conclusion: This was a carefully analyzed modeling study of idiopathic normal pressure hydrocephalus treatment made possible only by adjustable valve technology. With careful volumetric analysis, we found that changes in ventricular volume correlated with adjustments in valve pressure settings for those patients who improved clinically after shunting. This suggests that positive clinical responders retained parenchymal elasticity, emphasizing the importance of dynamic changes in this cohort.

Figures

FIGURE 1.

A and B, slicer software segmentation of the ventricular system of a subject without hydrocephalus (A ) used to produce the three-dimensional model of a normal, nonhydrocephalic ventricular system (B). C and D, slicer software segmentation of the ventricular system of a subject with INPH (C) used to produce the three-dimensional model of a hydrocephalic ventricular system (D).

FIGURE 2.

Three-dimensional bar graph illustrating the clinical outcomes for all patients included in the present study in each symptom category: gait, incontinence, and dementia.

FIGURE 3.

A , and B , three-dimensional model of the ventricular system measuring 180 ml ( A ), segmented from the initial postoperative CT scan date ( B ). C and D , three-dimensional model with a volume of 100 ml ( C ), and CT scan for the same patient 3 years later ( D ). E , graph illustrating our observation that changes in ventricular volume more closely follow changes in valve pressure than does the ventricular index, suggesting that ventricular volume would be a more accurate means of monitoring hydro-cephalus. Ventricular volume (in milliliters) and valve pressure (in millimeters of H 2 O) are graphed on the left axis, and the ventricular index is graphed on the right axis. Time measured in weeks after initial shunt implantation is illustrated on the x axis.

FIGURE 4.

Frequency distribution curve illustrating the number of times across all subjects that ventricular volume was observed to either increase or decrease when the adjustable valve pressure remained constant. This bar graph illustrates the variability in ventricular volume at a given pressure, but it also illustrates that the majority of these variations in volume at a constant pressure are very small, between 0 and 20 ml.

FIGURE 5.

A , diagram plotting the average changes in ventricular volume (ΔV) for the corresponding changes in valve pressure setting (ΔP ) for those patients who experienced 100% clinical improvement. B , diagram plotting the average changes in ventricular volume (ΔV ) for the corresponding changes in valve pressure setting (ΔP ) for those patients who experienced only partial clinical improvement in presenting symptoms.