Learning Center: HEARING

ANATOMY OF THE EAR

Anatomically, the ear is divided into three main components: the outer ear, the middle ear, and the inner ear.

The outer ear or external ear is the external part of the ear, which consists of the visible auricle (also pinna) and the ear canal. It gathers sound energy and focuses it on the eardrum (tympanic membrane).

The visible part is called the auricle or pinna. It is composed of a thin plate of cartilage, covered with skin, and connected to the surrounding parts by ligaments and muscles.

From the pinna, sound waves move into the ear canal (also known as the external acoustic meatus) a simple tube running through to the middle ear. This tube leads inward from the bottom of the auricula and conducts the vibrations to the tympanic cavity and amplifies frequencies in the range 3 kHz to 12 kHz.

The middle ear is the portion of the ear internal to the eardrum, and external to the inner ear. The mammalian middle ear contains three small bones (the ossicles—maleus, incus, and stapes), which transfer the vibrations of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear is also known as the tympanic cavity and is surrounded by the tympanic part of the temporal bone. The Eustachian tube joins the tympanic cavity with the nasal cavity (more specifically, the nasopharynx), allowing pressure to equalize between the middle ear and throat.

The primary function of the middle ear is to efficiently transfer acoustic energy from compression waves in air to fluid–membrane waves within the cochlea.

The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:

• The cochlea, dedicated to hearing; converting sound pressure patterns from the outer ear into electrochemical impulses which are passed on to the brain via the auditory nerve.

• The vestibular system, dedicated to balance

The inner ear conducts information to the brain via the eighth cranial nerve, which is really two nerves together, the acoustic nerve and the vestibular nerve, sometimes called the vestibuloacoustic nerve.

AN EMERGENCY: SUDDEN SENSORINEURAL HEARING LOSS

It is not usually clear to a patient (or their general physician) whether a sudden hearing loss is sensorineural or conductive. When in doubt, an otolaryngologist’s evaluation can differentiate the two. If the hearing loss is sensorineural, time is of the essence, and prompt diagnosis and treatment may prevent permanent hearing loss.

Sudden sensorineural hearing loss is a loss of at least 30 decibels over three consecutive pitches that develops within 72 hours, usually in one ear. It often is noticed on waking or when using the telephone, and it may come with tinnitus, ear fullness or dizziness. It affects an estimated 5 to 27 per 100,000 people each year, and in about 90% of cases no cause is found ("idiopathic") [7]. The American Academy of Otolaryngology–Head and Neck Surgery guideline makes these main statements [7]:

• Distinguish sensorineural from conductive loss at the first visit (a tuning fork test can do this in the office), and obtain a hearing test promptly.

• Evaluate for a cause such as an acoustic neuroma, usually with an MRI. A CT scan of the head is not recommended for routine evaluation, and routine blood tests are not recommended.

• Corticosteroids (by mouth, by injection through the eardrum, or both) may be offered within two weeks of onset. The evidence for steroids as first treatment is not strong, partly because many patients recover on their own, but treatment is most likely to help when started early.

• Intratympanic steroid injections should be offered as "salvage" treatment when recovery is incomplete two to six weeks after onset.

• Hyperbaric oxygen therapy, combined with steroids, may be offered within two weeks of onset, or as salvage treatment within one month.

• Antivirals, blood thinners, vasodilators and antioxidants are not recommended for routine use.

• Counsel patients with permanent loss about hearing aids and other hearing rehabilitation.

Some recovery happens without treatment in an estimated 32% to 65% of patients, usually within two weeks [7]. Recovery is less likely with severe loss, dizziness, older age, and delay in treatment.

• Link to frequently asked questions and evidence-based answers on Sudden Sensorineural Hearing Loss on ENTHealth website.

HEARING AIDS

A hearing aid is a device designed to improve hearing by making sound audible to a person with hearing loss. Hearing aids are classified as medical devices in most countries, and regulated by the respective regulations. Small audio amplifiers such as Personal Sound Amplification Products (PSAPs) or other plain sound reinforcing systems are not designated as "hearing aids". PSAPs are mostly off-the-shelf amplifiers for people with normal hearing who need a little boost in volume in certain settings. Hearing aids contain a much higher level of technology prescribed to treat a diagnosed hearing loss. PSAPs are not regulated under the Food, Drug and Cosmetic Act because they are not intended to treat, diagnose or cure hearing impairment and do not alter the structure or function of the body. Modern hearing aid devices are computerized electroacoustic systems that transform environmental sound to make it audible, according to audiometric and cognitive rules. Modern devices also utilize sophisticated digital signal processing to try and improve speech intelligibility and comfort for the user. Such signal processing includes feedback management, wide dynamic range compression, directionality, frequency lowering, and noise reduction.

Modern hearing aids require configuration to match the hearing loss, physical features, and lifestyle of the wearer. The hearing aid is fitted to the most recent audiogram (hearing test) and is programmed by frequency. This process is called "fitting" and is performed by a Doctor of Audiology, also called an audiologist (AuD), or by a Hearing Instrument Specialist (HIS). The amount of benefit a hearing aid delivers depends in large part on the quality of its fitting

Hearing aids help. In a Cochrane review of randomized trials in adults with mild to moderate hearing loss, hearing aids produced large improvements in listening ability and in hearing-related quality of life (how much hearing loss limits daily activities and relationships) compared with no hearing aids [6]. Even so, only about 1 in 7 Americans age 50 and older with hearing loss uses hearing aids [2]. Common reasons are cost, stigma, and the belief that the loss is not bad enough.

Since 2022, the U.S. Food and Drug Administration has allowed over-the-counter (OTC) hearing aids for adults with perceived mild to moderate hearing loss, sold without a prescription or hearing test. In a randomized trial of 64 adults, a self-fitted OTC hearing aid with remote support gave results similar to an audiologist-fitted hearing aid after six weeks [8]. OTC aids are a reasonable option for many people with mild to moderate loss. A medical evaluation and hearing test are still recommended first if the loss is sudden, worse in one ear, accompanied by ear pain, drainage, dizziness or tinnitus in one ear, or more than moderate, because these point to problems hearing aids alone do not address.

COCHLEAR IMPLANT

A cochlear implant (CI) is a surgically implanted neuroprosthetic device to provide a person with moderate to profound sensorineural hearing loss a modified sense of sound. CI bypasses the normal acoustic hearing process to replace it with electric signals which directly stimulate the auditory nerve. A person with a cochlear implant receiving intensive auditory training may learn to interpret those signals as sound and speech.

The implant has two main components. The outside component is generally worn behind the ear, but could also be attached to clothing, for example, in young children. This component, the sound processor, contains microphones, electronics that include Digital Signal Processor chips, battery, and a coil which transmits a signal to the implant across the skin. The inside component, the actual implant, has a coil to receive signals, electronics, and an array of electrodes which is placed into the cochlea, which stimulate the cochlear nerve.

The surgical procedure is performed under general anesthesia. Surgical risks are minimal but can include tinnitus, facial nerve injury (temporary or permanent) and dizziness.

From the early days of implants in the 1970s and the 1980s, speech perception via an implant has steadily increased. Many users of modern implants gain reasonable to good hearing and speech perception skills post-implantation, especially when combined with lipreading. One of the challenges that remain with these implants is that hearing and speech understanding skills after implantation show a wide range of variation across individual implant users. Factors such as duration and cause of hearing loss, how the implant is situated in the cochlea, the overall health of the cochlear nerve, but also individual capabilities of re-learning are considered to contribute to this variation, yet no certain predictive factors are known.

Cochlear implants are considered when hearing aids no longer provide enough speech understanding. In a systematic review of 42 studies of adults, a cochlear implant in one ear produced significant improvement in understanding speech and in quality of life, and implants in both ears added better ability to tell where sounds come from [9]. An international consensus panel concluded that implantation is the standard of care for adults with severe to profound hearing loss who get limited benefit from hearing aids, that candidacy has widened over time to include people with some remaining hearing, and that cochlear implants remain underused [10]. Testing for candidacy includes a hearing test with word and sentence understanding while wearing well-fitted hearing aids, imaging of the inner ear, and counseling about expectations and rehabilitation.

Ear fluid

• Link to Understanding Ear Fluid (and how it is different from infection) on the ENTHealth website. (My rating: C)

• Link to Treating and Managing Ear Fluid on theENTHealth website. (My rating: B)

• Link to evidence-based information on speech and language development in children as it relates to ear fluid. (My rating: A)

Ear fluid (otitis media with effusion) causes a temporary conductive hearing loss, and in adults fluid in only one ear deserves an examination of the back of the nose. Causes and treatment, including ear tubes, are covered on the ear infections and ear pressure pages.

Tinnitus

Tinnitus is the perception of sound when no corresponding external sound is present. While often described as a ringing, it may also sound like a clicking, buzzing, hiss, or roaring. Tinnitus is usually, but not always associated with hearing loss, and may be considered as a low signal-to-noise ratio from the ears.

Tinnitus may have no cure, but there are several treatments for this vexing problem. In brief, distracting noise (such as “white noise"), use of hearing aids, getting good sleep, getting daily exercise, and avoiding known dietary triggers (caffeine, ibuprofen and similar medications, apple cider vinegar, among others), alcohol, avoiding topical causes (sunscreen), and even cognitive behavioral therapy may help. Of course, prevention of tinnitus or its progression is important, and this is accomplished by avoiding excessive noise exposure and avoiding medications that hurt the inner ear (such as certain malaria medications and intravenous antibiotics called aminoglycosides).

• “How Can I Lessen the Impact of Tinnitus” at ENTHealth.org.

• Tinnitus information and resources from the American Speech and Language Association

Tinnitus is covered in detail, with references, on the tinnitus page.