Thresholds of resistance to CSF outflow in predicting shunt responsiveness

Objectives: Disturbances in cerebrospinal fluid (CSF) absorption capacity represent one of the primary causes of normal pressure hydrocephalus (NPH). The resistance to CSF outflow (Rout) may reflect the severity of this disturbance and has been used as a supplementary parameter to predict shunt responsiveness. However, there is no widely accepted threshold of Rout in this scenario. This study aimed to determine the most appropriate threshold through meta-analyses. Methods: A total of four previously reported cutoff values of Rout (10, 12, 15, and 18 mmHg/ml/minutes) were selected as potential thresholds. A systematic review of existing studies involving NPH, shunt surgeries, and Rout was conducted. The pooled results from retrieved articles were subjected to statistical analyses. Results: A total of nine studies were included in the meta-analyses based on the available preoperative Rout and postoperative improvement of subjects. The odds ratios of the four thresholds were 2.82, 3.58, 2.72, and 2.38 for 10, 12, 15, and 18 mmHg/ml/minutes of Rout, respectively. The Rout of 12 mmHg/ml/minutes yielded high accuracy (72.95%), high sensitivity (80.26%), and moderate specificity (46.79%). Discussion: The presented study conducted meta-analyses and revealed that a Rout of 12 mmHg/ml/minutes is the most suitable threshold for predicting shunt responsiveness in NPH patients.