Predictors of distal malfunction after ventriculoperitoneal shunting for idiopathic normal pressure hydrocephalus and effect of general surgery involvement

Objectives: Distal obstruction is a common cause of shunt failure and need for revision in patients undergoing ventriculoperitoneal shunting (VPS) for idiopathic normal pressure hydrocephalus (iNPH). Patients and Methods: Records of patients with iNPH treated with VPS between 2001 and 2017 were reviewed. Patients undergoing initial shunt placement at our institution were included for analysis and the incidence of revision surgery due to distal obstruction was noted. Risk factors for distal obstruction were identified using a stepwise Cox proportional hazards model. Results: There were 341 patients included for analysis. Assistance from a general surgeon in placement of the peritoneal catheter was provided in 54 patients (15.8%). Shunt revision was necessary in 69 patients (20.2%), with 17 patients (5.0%) found to have a distal malfunction. On univariate analysis, increasing age was associated with reduced risk of distal malfunction (Unit RR 0.92, 95% CI 0.89–0.96; p < 0.001). BMI ≥ 38.9 (RR 6.60, 95% CI 1.84–19.00), prior abdominal surgery (RR 2.95, 95% CI 1.11–7.70; p = 0.032), and fixed-setting valve (RR 6.24, 95% CI 1.27–112.72; p = 0.020) were associated with increased likelihood of distal malfunction. General surgery involvement had no effect on distal malfunction rates (OR 1.30, 95% CI 0.25–3.21; p = 0.693). On multivariate analysis, increasing age (Unit RR 0.92, 95% CI 0.89–0.95; p < 0.001) and prior abdominal surgery (RR 3.30, 95% CI 1.23–8.71; p = 0.019) were independently associated with decreased and increased risk of distal obstruction, respectively. Conclusions: We identify multiple factors associated with distal shunt obstruction, and found that general surgery assistance was not protective against distal malfunction. These data may aid in the risk-stratification of patients undergoing VPS for iNPH.