Procedure Practice 06/15/99 - Coding Recommendations

Feature Article 06/15/99:

The Ear - Part 1

Structure and Function - Diseases and Disorders

The ear is the prime organ of hearing and equilibrium, two key functions in all facets of our everyday lives. This month, we begin a two-part study of the ear with a review of its anatomy and function and discussion of some common diseases and disorders. Next month, we will cover audiologic testing and surgical procedures performed on ear structures.
  

Structure and Function

The outer ear functions as a sound collector. The external ear consists of the outer portion of the ear that is visible on the side of the head, called the pinna or auricle, and the external auditory canal that leads to the tympanic membrane. The pinna is composed of skin and cartilage with muscular attachments in the back. The parts of the pinna are the helix at the top of the external ear; the tragus, which is the small wedge of cartilage at the front of the ear near the ear canal; the lobe which is the soft tissue at the bottom of the ear; and the external auditory meatus, the opening to the ear canal. The external ear canal is approximately one inch long and is shaped like an hourglass. Cerumen is produced by glands located in the skin of the outer ear canal. Cerumen traps dust and sand particles before they reach the eardrum. The walls of the outer one-third of the canal are made of cartilage, and those of the inner two-thirds are made of bone. The entire canal is lined with skin. Sound waves are channeled through the external canal to the tympanic membrane.

The middle ear is a pea-sized, air-filled cavity (tympanic cavity) separated from the outer ear by the paper-thin tympanic membrane (eardrum). The tympanic membrane is a thin, rigid, semitransparent membrane between the external and middle ear. It consists of a central core of connective fibrous tissue and elastic fibers, covered on both sides by epithelium. Attached to the eardrum are the three tiny auditory ossicles, the malleus, the incus, and the stapes, often referred to as the hammer, anvil, and stirrup because of their respective shapes. These tiny bones transmit sound from the eardrum to the inner ear. Part of the malleus is directly attached to the inner surface of the eardrum and part forms a small joint-like connection with the incus. A small projection from the incus extends downward and connects to the stapes. The base of the stapes, called the footplate, sits over the oval window, an opening in the bony wall of the middle ear cavity. Three additional openings are also located within the middle ear. The round window is a membrane-covered opening below the oval window that opens into the cochlea of the inner ear. The eustachian tube is an opening on the front wall of the middle ear that leads to the upper part of the pharynx behind the nose. The eustachian tube permits air into the middle ear. In order for its structures to vibrate freely, the middle ear must contain air at the same atmospheric pressure as air outside the ear. The aditus (attic) is an opening in the back wall of the middle ear above the eardrum. It contains the head of the malleus and the body of the incus and leads to the mastoid sinus.

The chorda tympani is another structure found in the middle ear cavity. Although unrelated to hearing, it is significant when performing surgical procedures. The chorda tympani is the branch of the facial nerve that carries taste sensation for the anterior two-thirds of the tongue and innervates the submandibular and sublingual salivary glands. During complex middle and inner ear surgeries, it sometimes is necessary to sacrifice the chorda tympani in order to treat the ear disease.

The inner ear structures begin with the antrum, a cavity in the temporal bone that communicates with the middle ear attic anteriorly and with the mastoid air cells posteriorly. Mastoid air cells are a system of sinuses within the mastoid area of the temporal bone. Each air cell is lined by a mucous membrane of epithelial cells over a thin periosteum. Situated deep within the mastoid bone is a complex structure called the bony labyrinth. Within the bony labyrinth is a delicate tubular membrane called the membranous labyrinth which contains a fluid called endolymph. The bony labyrinth has three parts: the semicircular canals, the vestibule, and the cochlea. The three semicircular canals are at the top of the inner ear and sit at right angles to each other. They are generally identified by their relative positions as the superior, lateral, and posterior canals. The semicircular canals are connected to the brain via the eighth cranial nerve. They contain tiny sensory cells called crista, which detect fluid movement within the canals and maintain balance. The canals then merge into the central cavity of the bony labyrinth, the vestibule. Lying just in front of the vestibule is the cochlea, a spiral-shaped structure that contains the organ of Corti. Within the organ of Corti are over 16,000 tiny hair cells hair that transmit sound waves from the ear through the auditory nerve to the brain as electric impulses.

The vestibulocochlear nerve (eighth cranial nerve or acoustic nerve) is a composite sensory nerve with two distinct components. It serves as a communications cable that connects the receptors of the inner ear with the information processing centers of the brain. Each of the two components of this nerve serves a separate function and carries specific information to a separate part of the brain; the acoustic portion relays sound information from the hair cells and the vestibular portion relays balance and equilibrium data from the baro receptors within the semicircular canals.

The process of hearing begins with the collection of sound waves by the outer ear structures. The waves are channeled to the eardrum which then vibrates. The vibration creates energy that is transmitted to the malleus which strikes the incus and activates the stapes. The stapes then vibrates in and out of the oval window. Vibration here creates fluid waves in the cochlea that stimulate the hair cells. Nerves associated with the hair cells transmit electric impulses to the auditory nerve which then relays them to the brain for interpretation and recognition of sound.
  

Diseases and Disorders

Conductive Hearing Loss

Conductive hearing loss is the impairment of passage of sound vibrations to the inner ear. Disease or obstruction in the external or middle ear causes a conductive hearing impairment. This impairment may be due to a variety of problems, for example, otosclerosis, middle ear effusion, cerumen impaction, or ossicular disruption. Conductive hearing loss is generally correctable with medical (e.g., hearing aids) or surgical therapy.

Conductive losses in children are common, especially before the age of 6. Most problems occur as the result of middle ear effusion due to an immature eustachian tube. Significant conductive hearing loss during this critical time of speech and language development can cause a lasting communication deficit if left untreated.

Conductive losses in adults are usually short-term problems due to cerumen impaction, upper respiratory infection, or temporary eustachian tube dysfunction. Persistent conductive losses usually result from chronic ear infections, otosclerosis, or trauma.
   

Sensorineural Hearing Loss

Sensorineural hearing loss results from deterioration of the cochlea and is usually due to loss of or damage to hair cells. Among the common causes of sensorineural deafness are noise trauma, ototoxicity, aging (presbycusis), and acoustic neuroma. Generally sensorineural hearing loss is not amenable to medical or surgical treatment, but it is often possible to prevent or stabilize the problem. If some functional hair cells exist, cochlear implants may be used to bypass the nonfunctional cells and stimulate the auditory nerve directly.

Sensorineural hearing loss in children may be congenital or due to meningitis or other inflammatory or infectious processes. Profound congenital deafness may go unrecognized by parents until a child is 12-18 months of age. For this reason, high-risk infants must be screened carefully so that early diagnosis and auditory rehabilitation can begin. Criteria for high-risk children include prematurity, congenital malformations of the head and neck or urinary tract, meningitis, exposure to teratogens in utero, and a family history of deafness.

Sensorineural hearing loss in adults is more common than in children. A gradually progressive, predominantly high-frequency loss with aging is typical. Other than aging, common causes of sensorineural loss include excessive noise exposure, head trauma, and some systemic diseases such as diabetes mellitus.
  

Congenital Atresia

Congenital atresia, or the absence of the external ear canal, is a birth defect which is almost always accompanied by other abnormalities of both the middle ear bones and the external ear. The degree of hearing loss brought about by the atresia varies. In most cases of atresia a bony plate separates the external ear from the contents of the middle ear and the tympanic membrane is not present. In cases of complete atresia no external ear canal is present, and the external auditory meatus is completely obstructed by skin. Other cases of atresia may demonstrate a small rudimentary external ear canal. Surgical reconstruction is done to rebuild the ear and restore any conductive hearing loss.
  

Congenital Microtia

Congenital microtia, another type of birth defect, is an abnormal condition in the growth of the external ear. Defects vary from minor abnormalities of the helical ear folds to a marked absence of ear development. The presence of a small tag of skin and cartilage may be the only indication of an external ear. Plastic reconstructive surgery is done based upon the degree of microtia.
  

Cerumen Impaction

Cerumen is a protective secretion produced by the outer portion of the ear canal. In most individuals the ear canal is self-cleansing. Pushing cerumen deeper into the ear canal in an effort to clean the ear with a cotton swab or other object generally causes impaction. Impacted cerumen may be removed with detergent ear drops, suction, irrigation, or mechanical manipulation.
   

External Otitis

This condition, also known as swimmer's ear, is an infection of the outer ear canal. Sometimes it is caused by a fungus (Aspergillus), but more often it is caused by gram-negative bacteria such as Proteus or Pseudomonas. When water gets into the ear, it may bring with it bacteria or fungus particles. Usually the water runs back out, the ear dries, and the bacteria and fungi don't cause problems. If water remains trapped in the ear canal, the skin gets soggy. Then the bacteria and fungi grow and infect the outer ear. Initial symptoms include a sensation of blockage and itching. Soon the ear canal becomes swollen and may drain a milky liquid. The external ear becomes very painful and tender to touch, especially on the tragus. Treatment includes protection of the ear from additional moisture and administration of anti-inflammatory eardrops.
  

Exostoses

Bony overgrowths of the ear canal are often small, nonobstructing and asymptomatic. They appear as skin-covered mounds in the ear canal and may obscure the tympanic membrane to some degree. Single exostoses are not significant unless they cause obstruction or infection. Multiple exostoses, which are generally acquired from repeat exposure to cold water, often progress and require surgical excision.
  

Serous Otitis Media

Fluid in the middle ear of children is common and is usually a result of eustachian tube dysfunction. The eustachian tube connects the back of the throat behind the nose with the middle ear. In children, the eustachian tube does not always work as efficiently as in adults. The adenoids, located near the nasal opening of the eustachian tube, may prevent normal functioning of the tube if inflamed. Allergies and sinus infections sometimes cause congestion around the opening of the tube and impair its capacity to open properly. All of these factors prevent air from entering the middle ear. Over time, the air in the middle ear is absorbed by the body and replaced by fluid. The fluid itself does not cause any damage to the ear, although its presence can impair hearing as well as serve as a growth medium for bacteria. Symptoms of serous otitis include a dull-appearing, immobile tympanic membrane, conductive hearing loss, and a sense of fullness within the ear. Treatment of serous otitis is aimed at drainage of trapped fluid. Decongestant medications and surgical insertion of a ventilating tube into the eardrum are common remedies.
  

Acute Otitis Media

When trapped middle ear fluid becomes secondarily infected with bacteria, acute otitis media results. The mucosal lining of the air-containing spaces within the temporal bone become infected and purulent material forms here and within the mastoid air cells. The most common pathogens both in adults and children are Streptococcus pneumoniae, Haemophilus influenzae, and Streptococcus pyogenes. Symptoms of ear pain, decreased hearing, and fever are common with this illness. Although antibiotic treatment will cure the infection, if the fluid in not cleared from the middle ear space then another infection develops once antibiotics are stopped. After repeated infections the bacteria may become resistant to certain antibiotics.

Decongestants are frequently used in an attempt to drain fluid from the middle ear. In some cases the fluid may resolve along with the infection, but because of the marginal function of the eustachian tube, a minor cold or other disturbance may then cause a buildup of fluid and lead to another ear infection.
  

Barotrauma

Individuals with eustachian tube dysfunction due to either congenital narrowness or acquired mucosal edema may be unable to equalize the barometric pressure exerted on the middle ear by air travel, rapid altitude changes, or underwater diving. The problem is usually most acute during airplane descent, when negative pressure within the middle ear causes the eustachian tube to collapse upon itself. Physicians generally advise patients to swallow, yawn, or chew gum in an effort to improve eustachian tube function and prevent middle ear injury. If negative middle ear pressure persists, myringotomy and insertion of ventilating tubes may be performed to alleviate the symptoms of pain and hearing loss and restore middle ear air pressure.
   

Mastoiditis

Acute suppurative mastoiditis usually evolves following weeks of untreated or inadequately treated acute otitis media. The bony septa within the mastoid cavity are slowly eroded by infection, and the air normally found in healthy mastoid sinuses is replaced with purulent, diseased tissue. Symptoms include postauricular pain and erythema with a spiking fever. Treatment with intravenous antibiotics and myringotomy permits drainage of infected debris. If this initial course of treatment fails, it is followed by surgical drainage of the mastoid.
  

Tympanic Membrane Perforations

A perforation is a hole in the tympanic membrane. Perforations may result from infections or injuries to the ear. Childhood perforations most commonly occur from infections and generally heal on their own. Symptoms of a perforation include drainage from the ear and bloody discharge. Flying with a severe cold can also perforate an eardrum due to changes in air pressure. Self-inflicted damage with a cotton swab or other device inserted into the ear is another common cause of eardrum perforation in adults and children. With local care and water protection, the perforation will usually heal spontaneously. In some instances, however, self-inflicted eardrum perforation can force eardrum skin into the middle ear and cause the development of a cholesteatoma. Therefore, perforations are usually examined under an operating microscope in order to avoid further complications.
   

Ossicular Chain Disruption

This condition is usually the result of other disease or trauma within the middle ear. Discontinuity of the ossicular chain this results in decreased sound transmission from the tympanic membrane to the oval window and conductive hearing loss. The ossicular chain may become completely disrupted, partially disrupted or healed with a fibrous union. Common causes of ossicular chain abnormalities include congenital malformations of the external auditory canal and ossicles, fusion of the ossicles to the surface of the middle ear, penetrating injuries with resultant fractures, cholesteatomas, and chronic inflammation. Various reconstructive surgical techniques are used to reestablish continuity of the ossicular chain.
  

Otosclerosis

Otosclerosis is a progressive disease with a marked familial tendency that affects bone surrounding the inner ear. Lesions involving the footplate of the stapes result in increased impedance to the passage of sound through the ossicular chain and cause conductive hearing loss. Excessive growth of bone around the stapes fixes it in place so that it can not vibrate properly. Otosclerosis may affect one or both ears and gradually causes progressive hearing loss as the bony growth gets larger. Recent studies suggest that pregnancy and birth control pills may make the bony growth occur more rapidly. Advancing age may cause the growth to slow. The hearing loss caused by otosclerosis is usually conductive. Surgery does not stop the growth of otosclerosis, but usually results in correcting the hearing loss.

Occasionally otosclerosis may cause permanent sensorineural hearing loss. In this condition, the otosclerotic bone impinges upon the cochlea and affects the hair cells. Sensorineural hearing loss and conductive loss may occur separately or together but are unrelated as far as treatment is concerned.
   

Meniere’s Disease

Meniere's disease, also called idiopathic endolymphatic hydrops, is a disorder of the inner ear. Although the exact cause is unknown, it probably results from an abnormality in the extracellular fluids of the cochlea. Meniere's disease is one of the most common causes of dizziness. In most cases only one ear is involved, but both ears are affected in about 15% of patients. Meniere's disease typically starts between the ages of 20 and 50 years. Men and women are affected in equal numbers.

The symptoms of Meniere's disease are episodic rotational vertigo (attacks of a spinning sensation), hearing loss, tinnitus (a roaring, buzzing, or ringing sound in the ear), and a sensation of fullness in the affected ear. Vertigo is usually the most troublesome symptom of Meniere's disease. It is defined as a sensation of movement when no movement is occurring. Vertigo is commonly produced by disorders of the inner ear, but may also occur in central nervous system disorders. The vertigo of Meniere's disease occurs in attacks of a spinning sensation and is accompanied by dysequilibrium (an off-balance sensation), nausea, and sometimes vomiting. The vertigo lasts for 20 minutes to two hours or longer. During attacks, patients are usually unable to perform activities normal to their work or home life.

Sleepiness may follow for several hours, and the off-balance sensation may last for days. Intermittent hearing loss may occur early in the disease, especially in the low pitches, but a fixed hearing loss involving tones of all pitches commonly develops over time. Loud sounds may be uncomfortable and appear distorted in the affected ear. The tinnitus and fullness of the ear may come and go with changes in hearing, occur during or just before attacks, or be constant. The symptoms of Meniere's disease may be only a minor nuisance, or can become disabling, especially if the attacks of vertigo are severe, frequent, and occur without warning.
  

Labyrinthitis

The exact cause of labyrinthitis is not known, but it frequently follows an upper respiratory tract infection. Patients with this condition suffer from continuous severe vertigo that may last from several days to over a week. Accompanying symptoms include tinnitus and hearing loss. Recovery takes several weeks, and during this time any rapid or sudden head movement may cause transient vertigo. Hearing usually returns to normal, but occasionally impairment is permanent.
  

Positional Vertigo

Postural or positional vertigo is a violent vertigo that lasts less than 30 seconds and is triggered by certain head positions. This type of vertigo can be caused by conditions that damage the crista within the semicircular canals. Various causes include injury to the inner ear, otitis media, ear surgery, or blockage of the artery to the inner ear.

Vertigo develops when a person lies on one ear or tilts the head back to look up. Abnormal involuntary eye movement (nystagmus) also occurs. Positional vertigo is usually a short-term problem that resolves on its own.
   

Herpes Zoster of the Ear (Ramsay Hunt's Syndrome)

When the herpes zoster virus infects the acoustic nerve, severe ear pain, hearing loss, and vertigo result. Small vesicles form on the outer ear and in the ear canal. Blisters may also form on the skin of the face or neck along the course of the infected nerve. If the swollen acoustic nerve impinges upon the facial nerve, the muscles on one side of the face may become paralyzed. Hearing loss may be temporary or permanent, and episodes of vertigo may last for several weeks. Treatment for herpes zoster is generally with the antiviral medication acyclovir. Pain medication and drugs to ease vertigo may also be used. When the facial nerve is compressed, surgical decompression of the nerve may be necessary to enlarge the opening through which the facial nerve leaves the skull.
   

Malignant Ear Tumors

• Basal cell tumors are the most common malignant tumors of the outer ear and external canal. Usually, chronic sun exposure causes basal cell cancers, particularly of the upper portion of the exposed ear. They begin as circular raised areas of skin with central crater-like ulcerations. Basal cell cancers are common in elderly individuals and people with very fair skin. Basal cell cancers grow very slowly. Because of this fact, they are easily cured if treated early. If ignored, however, a basal cell cancer requires extensive surgery to completely remove it. Basal cell cancers generally do not metastasize to other organs. They spread by increasing in size only.
     
• Squamous cell tumors are less common than basal cell cancers. However, squamous cell cancers are much more aggressive than basal cell cancers. They may occur on the external ear or occasionally within the middle ear and mastoid. Symptoms of middle ear or mastoid squamous cell tumor include pain and intermittent hemorrhage or drainage for extended periods of time. Hearing loss is often significant. Squamous cell tumors spread through the tissues surrounding the site of origin. In addition, squamous cell cancers of the ear can spread to the lymph nodes in the neck. Squamous cell cancers of the external ear look much like basal cell cancers at an early stage. They are generally not painful, but grow more rapidly than basal cell cancers. Since squamous cell cancers are more aggressive, surgical removal must be more extensive. When squamous cell cancers become large, surgery combined with radiation therapy may also be necessary.
    

Benign Ear Tumors

• Cholesteatomas are the most common of all middle ear tumors. They are benign tumors that arise from a perforation of the tympanic membrane with ingrowth of skin into the middle ear. They may also appear congenitally from an epidermoid formation. As they grow, cholesteatomas resemble an onion peel of white skin formed into a ball. They actively erode bone as they expand and often invade the mastoid. Symptoms include hearing loss, dizziness, and recurring discharge from the ear. Very small cholesteatomas are removed through the ear canal. Larger tumors require an incision behind the ear to expose the tumor adequately. If the tumor has eroded through the bony wall between the middle ear and mastoid, the surgeon must perform a more radical operation in which the wall is completely removed. The result is an open cavity that will require life-long follow-up. This procedure is generally reserved for only the most invasive and destructive cholesteatomas.
    
• Polyps sometimes develop in the middle ear. They appear as grape-like clusters of inflamed tissue within the middle ear and mastoid. Polyps are a reddish color and bleed easily with any manipulation. They may be indistinguishable from more serious problems of the middle ear and mastoid. In most cases of advanced polyps and inflammation of the middle ear, surgical excision is necessary.
    
• Cholesterol granulomas are masses of gelatinous material within the mastoid and middle ear caused by hemorrhage into the mastoid and middle ear. The granuloma appears bluish-black upon examination of the tympanic membrane. As the material organizes, it adheres to the mastoid and middle ear and causes damage to internal structures. Surgical ventilation of the middle ear via insertion of a ventilating tube is helpful. In aggressive cases, surgical excision of all of the cholesterol granuloma is necessary. In most cases, a large bore ventilating tube is inserted into the eardrum and left in situ for prolonged periods of time to prevent recurrence of the granuloma.
    
• Acoustic neuromas are one of the most common intracranial neoplasms. They are benign tumors of the vestibular division of the eighth nerve near the inner ear. This tumor (called a "schwannoma") arises from the myelin forming cells (Schwann cells) of the 8th cranial nerve at the point where the peripheral portion of the nerve enters the brain (Hensen's node). Immediately associated with this nerve is the 7th cranial nerve that controls the muscles of the face, salivation, tearing, and taste. The tumor grows next to the brain stem, and when enlarged may actually compress it. Larger tumors also may involve the swallowing nerves (cranial nerves 9 and 10) below as well as the 5th nerve above which controls sensation to the face and eye. Patients may present with any combination of symptoms related to malfunction of these nerves, depending on the size, the pressure and location of the tumor. Acoustic neuromas may be unilateral or bilateral. Symptoms may develop at any age, but usually occur between the ages of 30 and 60 years. Bilateral acoustic neuromas are hereditary. Inherited from one’s parents, these tumors result from a genetic disorder known as neurofibromatosis-2 (NF2). Affected individuals have a 50 percent chance of passing this disorder on to their children. Unlike those with a unilateral acoustic neuroma, individuals with NF2 usually develop symptoms in their teens or early adulthood. Because of the symptomatology and the danger of brain involvement, surgery is required to excise the neuroma.
    
• Glomus tumors (glomus tympanicum) are benign tumors of the middle ear that arise from the abnormal growth of one or more glomus bodies. Glomus bodies are tiny baro receptors in the middle ear that regulate the oxygen pressure in the middle ear and mastoid. Glomus tumors are highly vascular and appear as a red ball or mass behind the eardrum. The eardrum may pulsate if the tumor is in contact with the undersurface of the eardrum. This symptom is called pulsatile tinnitus. As the tumor expands within the middle ear, it can grow into the mastoid or through the wall between the middle ear and mastoid and deeply infiltrate the bone. The tumor may also wrap around and infiltrate areas around the facial nerve, become attached to the jugular vein or carotid artery, and in extreme cases invade brain tissue.
    
  Though they do not metastasize, their local invasiveness makes large glomus tumors highly destructive and difficult to remove. Most localized glomus tumors are approached through the ear canal and destroyed with an Argon laser. The laser allows the surgeon to vaporize only tumor tissue and preserve the auditory ossicles within the middle ear. When a glomus tumor extends into the mastoid, it is necessary to make an incision behind the ear and open the mastoid bone. If the tumor has invaded bone and entered the brain, intracranial surgical excision of the tumor may be necessary. Depending on the size of the tumor, this part of the surgery is done in conjunction with a neurosurgeon. It can also be staged and performed at a separate operation. Staging is often chosen when very extensive tumors invade the brain.

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