[Derivation of cerebrospinal fluid: consequences on inner ear biomechanics in adult patients with chronic hydrocephalus]

Abstract

Background and purpose: Patients suffering from hydrocephalus are often treated by the surgical placement of a shunt, directing the excess of cerebrospinal fluid towards another body compartment. However, the degree of clinical improvement is variable and the dynamics of cerebrospinal fluid pressure in shunted hydrocephalus is poorly understood. A recently developed noninvasive technique makes it possible to follow pressure variations: it is based on otoacoustic emissions, sounds naturally emitted by the cochlea and routinely detected in audiology. When cerebrospinal fluid pressure changes, emissions undergo a phase shift while crossing the oval window. The goal of this work is to study how this shift is affected by shunt placement.

Method: Otoacoustic emissions were recorded repeatedly in 22 adult patients who suffered from chronic hydrocephalus. Their phase shifts were measured, in sitting and recumbent positions, before and after surgical placement of a ventriculo-peritoneal shunt (Sophysa SM8).

Results: Postural shift in normal subjects is a phase lead, and this outcome was found in 17 of 22 patients preoperatively. After shunt placement, the postural effect became a phase lag in 18 patients of 20. In a given posture, sitting or recumbent, phase shifts changed from pre to postoperative measurements in a systematic manner.

Conclusion: Otoacoustic emissions respond in a characteristic way to posture changes in normal adults, and having received a shunt for chronic hydrocephalus reverses the effect, presumably in relation to the existence of a "vacuum" in the inner ear.