Ventricular Volume Is More Strongly Associated with Clinical Improvement Than the Evans Index after Shunting in Idiopathic Normal Pressure Hydrocephalus

BACKGROUND AND PURPOSE

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.

MATERIALS AND METHODS

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.

RESULTS

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).

CONCLUSIONS

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.

Perioperative risk factors for short term shunt revisions in adult hydrocephalus patients

OBJECTIVES

The aim of this study was to prospectively study perioperative variables associated with revision after shunt surgery for adult hydrocephalus.

METHODS

Two protocols were designed to prospectively study perioperative risk factors during shunt insertion. Over 10 years (1995-2004), 450 adult (age >16 years) patients with first time shunt implantations were studied. Patients who had been treated with endoscopic third ventriculostomy were excluded from the study. All shunts were designated as meeting one of two end points: (1) shunt failure requiring revision within 6 months or (2) no shunt failure within 6 months. Shunt revision within 6 months postoperatively was considered to be related to the shunting procedure.

RESULTS

85 shunt revisions were performed within 6 months after insertion. During the study period the revision rate declined from 21.1% to 9.1%. Revision rates were the same for ventriculoperitoneal (n = 411) and ventriculoatrial (n = 39) shunts. The predictive values of variables related to the patient, operating room, surgical technique and shunt system were analysed to determine shunt outcome.

CONCLUSIONS

Right frontal placement of the ventricular catheter was associated with the lowest rate of revisions. Adjustable valves were associated with a lower risk for shunt revision. Shunt revision rates did not differ between ventriculoperitoneal and ventriculoatrial shunts.