Deafness caused by cochlear and postcochlear lesions is called sensorineural deafness, with cochlear lesions being the most common, and the resulting deafness is also called cochlear or sensorineural deafness. The postcochlear lesions include the auditory nerve and the central auditory conduction pathway, so the deafness caused by postcochlear lesions is also called postcochlear deafness, neurological deafness or central deafness.
I. Cochlear deafness
[Etiology
1. Congenital: It can be divided into hereditary deafness caused by genetic or chromosomal abnormalities, and non-hereditary deafness caused by maternal factors during pregnancy or delivery.
2. Noise: Strong noise exposure can lead to mechanical or metabolic damage to the cochlea, which in turn can cause deafness.
3.Trauma: Temporal bone fracture or pneumatic injury can lead to vagal concussion or vagal contusion, which can cause deafness.
4.Infection: Ear infection invading the bone vagus or membrane vagus of the inner ear can lead to vaginitis.
5. Ototoxic drugs: Some drugs have toxic effects on the inner ear hearing or vestibular function, which in turn can cause deafness or vestibular symptoms. Common ototoxic drugs include aminoglycoside antibiotics, antimalarials, antineoplastic agents, salicylates for pain and tab diuretics, etc.
6. Immune factors: Autoimmune syndromes can lead to asymmetric cochlear deafness in both ears, such as Cogan’s syndrome, Wegener’s granulomatosis, and primary inner ear autoimmune disease.
7. Age factor: Degenerative changes in the inner ear can occur along with aging, which in turn can cause hearing loss.
8. Sudden deafness: The cause is often unknown and manifests as a sudden onset of cochlear hearing loss.
9.Other: including inner ear blood supply disorders, metabolic diseases, cochlear otosclerosis, etc.
Clinical manifestations
1. Hearing damage: manifested as deafness and auditory distortion. Deafness can occur suddenly, such as sudden deafness; however, it usually shows slowly progressive deafness, such as senile deafness; in addition, there are some cochlear deafness, once the causative factors disappear, the degree of deafness and maintenance of stability, such as drug and noise deafness.
2. Tinnitus: Cochlear deafness is often accompanied by subjective tinnitus, the tone and degree of which vary depending on the cause.
3. Vestibular symptoms: Cochlear deafness may be accompanied by vestibular symptoms, such as vertigo and balance disorders.
Diagnosis
1.History: It is necessary to clarify the history of noise exposure, history of head trauma, history of otitis media, family history and history of ototoxic drug application.
2.Examination
(1) Otoscopic examination: normal.
(2) Audiological examination: pure tone audiogram shows increased air and bone conduction thresholds, especially high frequency hearing loss; normal acoustic impedance; otoacoustic emission disappears; auditory brainstem electrical response waveform may disappear, if present, the I-V wave interval is normal.
(3) Imaging examination: CT of temporal bone can show the bone vagus changes caused by deformity and trauma; MRI is used to exclude the auditory nerve and brainstem lesions.
Treatment
1.Medication: There is no effective treatment drug yet. According to different causes, the drugs often used include vasodilators, blood viscosity reducing drugs, thrombolytics, B vitamins, hormones, antimicrobials and antivirals.
Hearing aids: Hearing aids are sound amplification devices that are mainly used for patients with moderate to moderately severe deafness.
3.Cochlear implant: Cochlear implant is an acoustoelectric conversion electronic device that includes two parts: implant and speech processor, and is suitable for patients with profound deafness and total deafness.
Post cochlear deafness
[Etiology
1.Tumor: Tumor of the internal auditory canal and pontocerebellar horn, such as auditory neuroma.
2, Vascular compression: microvascular compression of the auditory nerve in the pontocerebellar horn, such as the anterior inferior cerebellar artery and posterior inferior cerebellar artery.
3.Auditory neuropathy: Binaural sensorineural deafness with unexplained, mainly low-frequency hearing loss, with no ABR elicitation or obvious abnormalities, but normal otoacoustic emissions.
4.Trauma: such as transverse temporal bone fracture.
[Clinical manifestations
The symptoms of retrocochlear deafness are basically the same as those of cochlear deafness, but patients with retrocochlear deafness often have poor speech resolution.
[Examination].
1.Otoscopic examination: normal.
2, Audiological examination: pure tone audiogram is the same as cochlear deafness; acoustic impedance is normal; otoacoustic emission is normal; auditory brainstem electrical response waveform may disappear, and if present, the I-V wave interval is prolonged.
3.Imaging: MRI is the preferred method to diagnose lesions of the internal auditory tract, pontocerebellar horn and brainstem.
Treatment
1.Medication: There is no effective treatment drug.
2.Hearing aid: The application of hearing aid is controversial, and the main problem is that it cannot improve the speech resolution.
3.Cochlear implantation: For auditory neuropathy, there are preliminary reports of cochlear implantation.
4.Auditory brainstem implantation: For bilateral auditory neuroma and bilateral traumatic postcochlear deafness, auditory brainstem implantation can be chosen.
5. Etiological treatment: such as surgical resection of tumors of the internal auditory tract and the pontocerebellar horn of the cerebellum.