Valve inclination influences the performance of gravity-assisted valve

The performance of GAV may be affected by its inclination as a tantalum sphere in the valve, which generates a downhill force in proportion to the sine of the angle with respect to level. Accordingly, the aim of this study was to evaluate the effect of valve inclination relative to the vertical on shunt performance.

In 24 adult patients who underwent ventriculoperitoneal shunting using a GAV for hydrocephalus, valve inclination relative to the vertical was measured using AP and lateral projections of skull x-rays that were taken in a standing position, and the relationship between valve inclination and ventricular volume change after ventriculoperitoneal shunting in CT scans was evaluated.

The Pearson correlation coefficient between valve inclination in a sagittal plane and ventricular volume change was -0.768 (P < .01), whereas lateral valve inclination had no correlation with ventricular volume change. Eleven patients with a posterior valve inclination relative to the vertical exhibited a greater ventricular volume reduction of 34.1% +/- 8.2% compared to the volume reduction of 13.4% +/- 9.2 % in 13 other patients with an anterior valve inclination (P = .000). Two (40%) of 5 patients with a severe anterior valve inclination of more than 20 degrees relative to the vertical underwent shunt revision for underdrainage.

A severe anterior inclination of the valve by more than 20 degrees relative to the vertical can lead to underdrainage owing to an increased OP in a lying position, especially in patients who are nonambulatory at the time of GAV implantation.