Normal-pressure hydrocephalus is associated with increases in the intracranial pressure during the night sleep. Sleep apnea also increases the intracranial pressure during the apneic spells. When patients are operated the distal part of the shunt is inserted inside the abdominal cavity, which pressure also increases during the sleep apnea episodes. this is particularly important considering that the recumbent position used to sleep further increases the intraabdominal pressure and that impairs the CSF drainage through the shunt system. The purpose of this study is to analyze the intracranial and intraabdominal pressures during the sleep, particularly during the sleep apnea episodes to see which shunt should be used, to which cavity should be drained (peritoneum or heart) and if correcting the sleep apnea has some positive result on the hydrocephalus symptoms.

Chronic hydrocephalus in adults, also known as normal pressure hydrocephalus or normal pressure hydrocephalus, occurs with the classic Hakim-Adams triad, gait ataxia, or "magnetic gait", urinary incontinence and dementia.

Most of the cases have an idiopathic origin and are the only potentially reversible cause of dementia with surgical treatment (by shunting the cerebrospinal fluid or CSF from the lateral ventricles or the thecal sac to the peritoneal cavity or the right atrium), so it is especially important to diagnose it and treat it properly.

Unfortunately, and despite all the diagnostic arsenal, the results of treatment using cerebrospinal fluid shunts (lumbo-peritoneal or ventricle-peritoneal), even in the best series, show 20-25% of poor results. These poor results have been attributed to many factors, including associated cerebral vascular pathology problems, co-existing dementia symptoms not always well diagnosed, Parkinson's disease, and, lastly, alterations in ventilatory rhythm. during the night, specifically obstructive sleep apnea or OSA.

In reality, the name of normotensive hydrocephalus or hydrocephalus at normal pressure is inaccurate because the intracranial pressure does rise and very markedly during sleep, particularly during the REM phase of sleep. What is no longer so well known is because of such significant increases in intracranial pressure occur. One possible explanation would be that obstructive sleep apnea causes increased intracranial pressure. But it remains to be clarified whether all patients with adult chronic hydrocephalus have sleep apnea, the mechanism of action, and to what extent the treatment of hydrocephalus acts on sleep apnea and vice versa.

Another aspect to consider is that the cerebrospinal fluid shunts work by the pressure gradient between the intracranial cavity and the cavity into which the cephalo-spinal fluid is drained66, usually the peritoneal fluid. During sleep apnea, there should be an increase in intra-abdominal pressure, which would result in the ventricle-peritoneal and lumbo-peritoneal shunts working suboptimally precisely at the time of day when they are most needed, that is when intracranial pressure increases. But this correlation has never been investigated or at least there are no publications about it.

Therefore, it is necessary to know the relationship between intracranial pressure, sleep apnea, and intra-abdominal pressure at night. With these data, it will be possible to better understand the dynamics of the circulation of the cerebrospinal fluid during the night (when it is more pathological in chronic hydrocephalus in adults), what type of bypass valve is the most indicated (whether or not it must have an anti-system siphon if it must be a gravitational or flow valve) and in which patients the implantation of a ventricle-atrial shunt may be an option to consider.

Inclusion Criteria:

• Clinical condition compatible with normal-pressure hydrocephalus

Exclusion Criteria:

• Cerebral vascular disease
• Dementia not due to normal-pressure hydrocephalus
• Parkinson's disease

Patients will not be informed of the final treatment decided