Hearing Impairment

Hearing impairments and impairments of vestibular function are also commonly noted. Hearing impair­ment may occur secondary to several causes: central processing deficit, peripheral nerve damage, cochlear injury, or disruption of the middle ear structures.

Vestibular impairments have already been men­tioned in the discussion on balance. Vertigo secondary to vestibular impairment commonly resolves within six months of injury (112,113), but electronystagmo­gram abnormalities can persist for years (114).

Central auditory processing impairment occurs with damage to tracts or cortical tissue. In such individuals, pure tone audiometry is normal, but other studies, such as speech discrimination, or late wave forms of brain­stem auditory evoked potentials are abnormal (115). Central auditory impairment is difficult for most fam­ilies to understand. Their intuitive conclusion is that hearing is related to the ear, so they frequently antic­ipate that interventions such as a hearing aid may be helpful.

Hearing loss may be conductive in nature because of disruption of the ossicles or cerebrospinal fluid or blood in the middle ear. Both of these types of injuries are frequently associated with fractures of the tempo­ral bone (116). Conductive hearing loss usually recov­ers spontaneously in about 3 weeks. If it persists for more than3 weeks (particularly for >30 db) a repeat audiogram and exploration of the middle ear is recom­mended (116). Problems related to fluid in the middle ear usually resolve spontaneously.

Sensorineural hearing loss may also be seen, but less often than conductive hearing loss (116,117). Sensorineural hearing loss is commonly noted at higher frequencies (117) and is associated with inner ear pathology (112,116). Marked variation is seen in the recovery of sensorineural hearing loss (116).

There may be trauma to the eighth cranial nerve, or injury to the labyrinthine capsule, or labyrinthine concussion, which may result in hearing loss because of the transmission of high-energy vibrations and a pattern similar to the hearing loss after prolonged noise exposure (118). Injuries to the labyrinthine cap­sule and the eighth cranial nerve are frequently asso­ciated with basilar skull fracture.