The aim of this study is to compare the value of multifrequency tympanometry between patients with surgical indication of treatment for a Chiari type I malformation and healthy volunteers.

Prevalence of Chiari type I malformation in population is between 0.1% and 0.5%. Chiari type I malformation is responsive in perturbation of the cerebro spinal fluid flow at the cranio-cervical junction. Those perturbations caused headaches, and various otological symptoms (dizziness, tinnitus, vertigo, nystagmus, hypoacousis…). The surgical treatment consists in an occipital craniotomy to restore the cerebro spinal fluid flow at the cranio-cervical junction. Symptoms are due to increasing of the pressure in the cerebellar fossa. 81% of the patients with Chiari type 1 malformation suffer of sub clinical otological perturbations especially alteration of the vestibular test.

In the literature, hearing performance could be normalized after posterior fossa decompression. Furthermore, the multifrequency tympanometry measurement and particularly the width of conductance tympanograms at 2 kHz shows that variations of the cerebro spinal fluid pressure have consequences on the pressure of the perilymph.

Investigator's hypothesis is that tympanometry (conductance) could be an effective test to show the variation of the cerebro spinal fluid pressure.

Inclusion criteria:

• Chiari type I malformation proved at MRI or CT-scan with an indication of cranio cervical decompression.
• Patients between 18 and 60 years old.
• Patient should benefit of the national health care system
• Agreement of the patient

Inclusion criteria for healthy volunteers:

• Between 18 and 60 years old.
• Free of otologic pathology
• Benefit of the national health care system
• Agreement of the volunteers

Exclusion criteria:

• Acute hydrocephaly
• Other type of Chiari disease (induced…)
• Medical history of neurosurgery
• Contraindication for MRI
• Cophosis
• Chronic otitis
• Medical history of ontological surgery
• Tympanic perforation
• Disturbance of tonal audiometry with air bone more than 20dB in 4 frequencies with abolition of stapedial reflex
• Pregnant women or nursing women
• Protected adults by French laws

Exclusion criteria for healthy volunteers:

• Medical history of neurosurgery
• Cophosis
• Chronic otitis
• Medical history of ontological surgery
• Tympanic perforation
• Disturbance of tonal audiometry with air bone more than 20dB in 4 frequencies with abolition of stapedial reflex
• Pregnant women or nursing women
• Medical history of Chiari malformation
• Chronic headaches or neck pain
• Protected adults by French laws