cephaloceles are rare lesions of the petrous apex, inconsistently listed as meningoceles or arachnoid cysts. They're consistent with a herniation posterolateral of the Meckel cavum within the petrous apex. These lesions may be the cause of a symptomatology varied, or be discovered by chance in subjects who have not been asymptomatic. Currently, there is no evidence in the literature a simple, fast and reproducible radiological marker that allows for the diagnosis of cephaloceles of the petrous apex, in particular the small ones. The purpose of this study is to validate a radiological benchmark simple and reproducible, the trigeminal petrol line, in order to improve the diagnosis of petrous apex cephaloceles

Inclusion criteria:

• Major subjects (≥18 years old)
• patients who underwent an MRI with high resolution 3D T2 sequence between 01/01/2003 and 09/31/2020:
• 200 patients consulting for ENT pathology such as vertigo
• 9 patients presenting the radiological criteria in MRI of a cephalocele of the petrous apex according to the current data of the literature on a T2 3D HR sequence
• - Subject who has not expressed his opposition, after being informed, to the reuse of his data for the purposes of this research.

Exclusion criteria:

• Subject who expressed their opposition to participating in the study
• Kinetic Artifacts
• Subject under guardianship or curatorship
• Subject under safeguard of justice

Major subjects (≥18 years old) who underwent an MRI with high resolution 3D T2 sequence between 01/01/2003 and 09/31/2020:

• consulting for ENT pathology such as vertigo
• or presenting the radiological criteria in MRI of a cephalocele of the petrous