Hearing Loss

Hearing loss is a partial or complete reduction in the ability to detect sounds, and it is among the most prevalent sensory impairments worldwide. Audiologists classify hearing loss by the site of the problem: sensorineural hearing loss results from damage to the cochlea (the inner ear) or the cochlear nerve and its central pathways; conductive hearing loss reflects a mechanical problem in the outer or middle ear that impedes the transmission of sound vibrations; and mixed hearing loss has components of both. In the context of intracranial and skull base pathology, sensorineural hearing loss — particularly when it is unilateral (affecting one ear), progressive, or accompanied by other neurological symptoms — is an important indicator of a possible structural lesion that requires investigation.

Hearing loss relevant to brain and skull base pathology includes:

• Vestibular schwannoma (acoustic neuroma) — the most important tumor-related cause of unilateral sensorineural hearing loss; slow, progressive deterioration is the most common presentation, though sudden hearing loss may occur.
• Cranial nerve tumors and skull base tumors — meningiomas, paragangliomas, and other lesions in the cerebellopontine angle or temporal bone can compress the cochlear nerve.
• Temporal bone fracture following head trauma — a basilar skull fracture through the petrous temporal bone can sever the cochlear nerve or damage the labyrinth, causing profound, permanent hearing loss, often with associated tinnitus and vestibular symptoms.
• Meningitis — bacterial meningitis is a recognized cause of sudden bilateral sensorineural hearing loss due to direct cochlear inflammation.
• Age-related hearing loss (presbycusis) and noise-induced hearing loss — the most common causes of bilateral hearing loss in the general population; typically symmetric and gradually progressive.

The timing and pattern of hearing loss help distinguish benign from potentially serious causes. The following features warrant prompt evaluation:

• Unilateral hearing loss — any new, unexplained hearing loss affecting only one ear should prompt audiological assessment and MRI of the internal auditory canals to exclude vestibular schwannoma.
• Sudden sensorineural hearing loss — a medical urgency requiring evaluation and treatment within 24 to 72 hours, as prompt corticosteroid therapy improves the chance of recovery.
• Hearing loss associated with tinnitus, dizziness, or imbalance — particularly when all affecting the same side, a combination strongly suggestive of an eighth cranial nerve or inner ear lesion.
• Hearing loss following head trauma — should be evaluated to assess for temporal bone fracture or cochlear nerve injury.
• Progressive hearing loss over weeks to months — warrants audiological re-evaluation and imaging regardless of the patient's age.