In the literature, a dichotomous view of cerebral venous drainage is most commonly found. Thus, two drainage pathways are most often considered: the jugular vein network and the vertebral artery plexus. However, several clinical observations seem to indicate a much more complex situation.

The following hypothesis is therefore put forward: there are alternative drainage pathways to these main pathways, which are physiologically present and capable of draining a significant volume of blood. A set of alternative pathways, which can be described as "deep," has been described: in particular, drainage pathways surrounding the vertebral artery (vertebral artery venous plexus), epidural plexuses, and deep cervical veins. However, the so-called "superficial" systems (subcutaneous and muscular) do not appear to have been studied.

There appears to be a change in venous drainage of the craniocervical junction postoperatively (posterior cranial fossa surgery and posterior approach to the upper cervical spine).

These modifications would vary depending on the venous drainage configuration present in each patient. If this hypothesis is confirmed, it could have an impact on the management of each patient. Thus, if venous remodeling models are established, this could enable personalized perioperative patient management: better optimization of body position during installation in the operating room, more effective anticipation of potential intraoperative venous bleeding, and explanation of persistent headaches in the postoperative period due to insufficient compensation of venous drainage. Confirmation of this hypothesis would also improve the understanding of certain pathologies for which the venous hypothesis has been raised (chronic hydrocephalus in adults, idiopathic intracranial hypertension, etc.).

Inclusion:

The inclusion visit will take place during an initial neurosurgery consultation. If the patient meets the inclusion and exclusion criteria and wishes to participate in this study, the study investigator will obtain the patient's consent.

During this visit, a routine MRI will be performed if the patient has not already had one. In addition to the standard procedure, this MRI will include the study-specific T1 GRE GADO MRI sequence, which will add approximately 3 minutes to the usual examination. The patient will also undergo a routine neurological clinical examination and data about them will be collected (informative data about the patient (age, sex, BMI, etc.), medical history, neurological functional signs, reason for treatment, and neurological clinical examination).

First follow-up visit:

During hospitalization in the neurosurgery department, the patient will undergo a routine neurological clinical examination and data will be collected intraoperatively (duration of surgery, blood loss, ligation/clipping/any interventions on venous structures, intraoperative hemorrhage, other complications of all types) as well as early postoperative data (complications, types, headaches).

The time between the preoperative visit and surgery varies and may depend on the patient's surgical indication.

Second follow-up visit:

Finally, the patient will be asked to come to the neurosurgery department for a post-operative visit a few weeks after their surgery.

This visit is part of standard practice and includes a clinical neurological examination.

During this visit, a second MRI will be performed using the specific sequence for the study, T1 GRE GADO, which will add approximately 3 minutes to the routine examination. Data concerning the patient will be collected (complications, types, headaches).

Inclusion Criteria:

Patient:

• Adult
• Surgery of the posterior cranial fossa or posterior approach to the upper cervical spine, regardless of indication, performed in the neurosurgery department at Brest University Hospital
• Having undergone an MRI with T1 echo gradient sequence with gadolinium (T1 TFE GADO)
• Affiliated with a Social Security scheme
• Having given written consent to participate in the study

Exclusion Criteria:

• Pregnant or breastfeeding women
• Allergy to gadolinium
• Any contraindications to undergoing an MRI scan (incompatible medical device implant, claustrophobia, etc.)
• Patients unable to understand the protocol
• Patients under guardianship or conservatorship
• Patients subject to a future protection order, family authorization, or legal protection

All collected data that underlie results in a publication

Data will be available beginning three years and ending fifteen years following the final study report completion

Data access requests will be reviewed by the internal committee of Brest UH. Requestors will be required to sign and complete a data access agreement.