In modern medicine, doctors attempt to monitor all physiological variables to assess their evolution and to decide, based on their changes, the therapeutic attitudes to adopt. Furthermore, this helps to establish a forecast of the evolution to be expected.

The measurement of Intracranial Pressure (ICP) has become indispensable for managing brain pathology at the anterior and middle fossa level. Doctors generally carry out this measurement at the frontal level. However, experimental and clinical studies have shown that supra-tentorial ICP measurement does not precisely predict the ICP situation in the posterior fossa.

The increased ICP in the posterior fossa is directly responsible for the clinical deterioration and eventual death in patients with tumour, hemorrhagic, or ischemic pathology of the posterior fossa structures. Some of these lesions are treatable, and their effects reversible if the increase in ICP in the posterior fossa is controlled by pharmacological or even surgical means, preventing it from reaching high levels. This need for on-time ICP control is genuine in the cerebellar hemispheres' lesions, not so much in lesions involving the brainstem. Therefore, the increase in ICP in the posterior fossa needs to be known and documented to facilitate decision-making regarding the therapy to be adopted, be it medical or surgical.

It is known what the abnormal ICP levels are at the supratentorial level, but what is not known whether these same levels apply to the posterior fossa. In other words, what it is not know with certainty is whether the same levels of ICP in the posterior fossa and its elevation during the same time are going to have equally pernicious effects or these effects are greater or lesser. Doctors need to have tables of ICP values in the posterior fossa to help them decide when these values are in the physiological range. When posterior fossa intracranial pressure lye in the pathological range, and patients need pharmacological treatment or surgical decompression, knowing for sure the posterior fossa ICP is essential. Finally, when doctors also need to know when any therapeutic attempt is useless.

Currently, doctors only monitor the ICP at the supra-tentorial level and deduce the changes in the posterior fossa from the CT and MRI images, that is, the size of the lesions, the occlusion of the cisterns, the internal cerebral hernias (cerebellar tonsils, trans-tentorial hernia from bottom to top). However, doctors do not have a tool that can objectify the pathophysiological situation of the posterior fossa's structures in real-time.

Monitoring the posterior fossa ICP will help doctors in decision-making in patients with traumatic, hemorrhagic, ischemic, or tumour pathologies (in the latter case, in the postoperative period of posterior fossa tumours). This posterior fossa ICP measurement will lead to improvements in morbidity/mortality in this subgroup of patients.

The purpose of our study is to register the posterior fossa pressure in normal postoperative conditions and in patients with different kinds of posterior fossa pathologies. The aim of the study is to get a range of posterior fossa intracranial pressure values in physiological situations and then to get the same data in patients with posterior fossa pathologies. The ideal would be to monitor the posterior fossa ICP in normal subjects but this is something that does not seem ethically correct. That is why, instead, the posterior fossa ICP will be measured in posterior fossa post-operative time. These patients will have to be operated any way for their posterior fossa pathologies, and adding a posterior fossa ICP sensor does not seem a problem from the ethical point of view. In any case, patients will be asked to sign informed consent. The second aim of our study will be to compare the supratentorial (frontal area) ICP monitoring with the posterior fossa ICP monitoring to see if their values coincide or if there are deviations. This will help doctors to decide when posterior fossa ICP must be done and not to rely only on supratentorial (frontal) ICP monitoring.

1. A study will be done on 12 patients. The series published to date are very short.
2. Inclusion criteria: age 18 years, traumatic pathology, tumour, ischemic or hemorrhagic posterior fossa, GCS 8 or lower.
3. EXCLUSION CRITERIA coagulation disorders, fault multi-organic, multiple pathologies, head trauma open posterior fossa with output nerve tissue.
4. Inserting PIC level sensor above-tentorial (1 sensor PIC) and another level infra-tentorial (2nd sensor PIC).
5. Verification that the ICP sensor in the posterior fossa can be implanted at the same point as we implanted it in cadavers without more significant clinical repercussions than those seen with the insertion of the ICP at the supra-tentorial level. In that sense, we have to confirm the technique's safety at the selected point away from the lateral sinus and sigmoid sinus and the lateral part of the occipital shell. We must also verify that it is not incredibly annoying for patients (in any case, it will be patients in a coma and probably sedated), but it is about confirming that the movements of the patients do not cause problems in the ICP sensor of the posterior fossa and if they do will be sought (in collaboration with the manufacturer) technical amendments necessary to avoid any problems that go detecting
6. Data Collection ICP level supra and infra-tentorial. These data will be recorded continuously on a computer for later analysis.
7. Data analysis ICP supra and infra-tentorial comparing the figures obtained in the two compartments (the supra and infra-tentorial).
8. Analysis of the correlation or non-correlation between the supra-tentorial ICP and infra-tentorial ICP figures.
9. Correlating data PIC infra-tentorial with the clinical status of patients and their evolution.
10. Analysis of possible complications attributable to the inclusion of the ICP monitor posterior fossa, analyzing possible areas for improvement to minimize any possible risk. In particular, we will analyze the risk of bruising-hematoma in the cerebellar hemisphere at the insertion point.
11. Analysis of therapeutic decisions based on figures from the PIC in the posterior fossa.
12. Analysis of the results and their correlation with therapeutic attitudes adopted.
13. Preparation of recommendations.

Inclusion Criteria:

• minimum age of 18 years
• traumatic, tumor, ischemic, or hemorrhagic pathology of the posterior fossa
• GCS of 8 or less.

Exclusion Criteria:

• coagulation disorders
• multi-organ failure
• multiple pathologies
• open head trauma to the posterior fossa with leakage of nervous tissue

Patients with posterior fossa lesions, traumatic, neoplastic, ischemic, or hemorrhagic

To collect all the data and publish them