Abstract
Ventricular enlargement in idiopathic normal pressure hydrocephalus is often estimated using the Evans index. However, the sensitivity of the Evans index to estimate changes in ventricular size postoperatively has been questioned. Here, we evaluated the postoperative change in ventricle size in relation to shunt response in patients with idiopathic normal pressure hydrocephalus, by comparing ventricular volume and the Evans index. Fifty-seven patients with idiopathic normal pressure hydrocephalus underwent high-resolution MR imaging preoperatively and 6 months after shunt insertion. Clinical symptoms of gait, balance, cognition, and continence were assessed according to the idiopathic normal pressure hydrocephalus scale. The ventricular volume of the lateral and third ventricles and the Evans index were measured using ITK-SNAP software. Semiautomatic volumetric analysis was performed, and postoperative changes in ventricular volume and the Evans index and their relationships to postoperative clinical improvement were compared. The median postoperative ventricular volume decrease was 25 mL (P < .001). The proportional decrease in ventricular volume was greater than that in the Evans index (P < .001). The postoperative decrease in ventricular volume was associated with a postoperative increase in the idiopathic normal pressure hydrocephalus scale score (P = .004). Shunt responders (75%) demonstrated a greater ventricular volume decrease than nonresponders (P = .002). Clinical improvement after shunt surgery in idiopathic normal pressure hydrocephalus is associated with a reduction of ventricular size. Ventricular volume is a more sensitive estimate than the Evans index and, therefore, constitutes a more precise method to evaluate change in ventricle size after shunt treatment in idiopathic normal pressure hydrocephalus.
Highlights
BACKGROUND AND PURPOSEVentricular enlargement in idiopathic normal pressure hydrocephalus is often estimated using the Evans index
Clinical improvement after shunt surgery in idiopathic normal pressure hydrocephalus is associated with a reduction of ventricular size
We evaluated the correlation between postoperative change in the Idiopathic normal pressure hydrocephalus (iNPH) scale score and postoperative decreases in ventricular volume and the Evans index (EI), respectively, using regression models, assuming approximate normal distributions and adjusting for heteroscedasticity
Summary
Fifty-seven patients with idiopathic normal pressure hydrocephalus underwent high-resolution MR imaging preoperatively and 6 months after shunt insertion. The ventricular volume of the lateral and third ventricles and the Evans index were measured using ITK-SNAP software. Semiautomatic volumetric analysis was performed, and postoperative changes in ventricular volume and the Evans index and their relationships to postoperative clinical improvement were compared. Clinical assessments and MR imaging examinations were performed preoperatively and after 6 months in all patients. Two patients demonstrated shunt obstructions before the postoperative examinations. These 2 patients underwent shunt revision and were included in the study, with clinical assessment and MR imaging performed 6 months after the shunt revision. Seven patients demonstrated motion artifacts on preoperative (n 1⁄4 4) or postoperative (n 1⁄4 3) MR imaging and were excluded from the study.
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