What is the auditory system?
|Figure 10: Diagram of the auditory system|
The auditory system performs the functions of hearing. The sense of hearing is a fine-tuned, intricate process. A sound wave is collected by the outer ear and sent through the middle ear into the inner ear where auditory hair cells are located. Once auditory hair cells in the inner ear are stimulated via sound waves, an electrical signal is generated and transmitted from these hair cells to the auditory nerve (also called cranial nerve VIII). From the auditory nerve, this signal is finally sent to the brain and subsequently processed. Hearing loss may be present if a part of the outer, middle, inner ear or auditory nerve is damaged or missing.
What hearing abnormalities can be seen in children with PHACE syndrome?
Hearing loss is a relatively new finding associated with PHACE syndrome. The hearing loss is most often unilateral (on one side) and ipsilateral (the same side) to the hemangioma located on a child's face. Radiologic imaging studies have attributed this hearing loss in PHACE syndrome to intracranial hemangiomas affecting various auditory structures (see Intracranial Hemangioma section).
The 3 types of hearing loss associated with PHACE syndrome are conductive, sensorineural and mixed hearing loss.
- Conductive hearing loss occurs when sound is not conducted efficiently through the outer ear canal to the eardrum and the tiny bones, or ossicles, of the middle ear. The most common in PHACE syndrome is an intracranial hemangioma that occludes the Eustachian tube (part of the middle ear). Conductive hearing loss usually involves a reduction in sound level or loss of the ability to hear faint sounds.
- Sensorineural hearing loss occurs when there is damage to the inner ear or to the nerve pathways from the inner ear to the brain. An intracranial hemangioma that affects the auditory nerve can lead to this type of hearing loss in PHACE syndrome. Sensorineural hearing loss is usually permanent.
- Mixed hearing loss is a combination of conductive and sensorineural hearing loss. Although this has been seen in PHACE syndrome, it is thought to be caused by factors other than the PHACE syndrome itself (i.e. coincidence).
How are hearing abnormalities diagnosed and treated?
Children with PHACE syndrome will generally pass their initial newborn hearing screen, but may develop problems during the first year of life. Suspicions of hearing loss should be brought to the attention of the primary care physician. A referral to an otolaryngologist (ear-nose-throat doctor) or audiologist (hearing specialist) may be needed. If a child has hemangiomas on or around the ear and has been diagnosed with PHACE syndrome, a hearing test should be repeated during the first year of life.
If hearing loss is determined to be attributed to an intracranial hemangioma in the child, treatment to minimize the growth of the hemangioma can be started. Assistive devices are also available to improve hearing.
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