Structure of the ear

A diagrammatic cross-section of the external, middle and inner parts of the ear is shown in Figure 4.1.

Fig. 4.1 Cross-section of the whole structure of the ear.

THE EXTERNAL EAR

The externally visible part of the external ear is the pinna (Fig. 4.2). This is a structure covered by skin with an internal structure of cartilage (which is absent in the lowest part, the tragus).

Fig. 4.2 The pinna.

As well as the pinna, the external ear includes the external canal and peripheral surface of the tympanic membrane. The skin of the external canal contains normal epithelium with hair follicles and apocrine glands. It is the combination of desquamated skin and the ceruminous secretions of the apocrine glands that form wax. Wax is protective to the ear but over-accumulation or impaction reduces the conductive element of hearing. The external canal is straight in children (making the tympanic membrane easier to see) but in adulthood the canal passes through an angle of descent distal to the observer. The angle formed by the tympanic membrane and the external canal makes an acute-angled recess (the anterior recess) which can be difficult to visualise, and wax, discharge or a foreign body may be difficult to locate and remove. This difficulty may be compounded by the isthmus if it is narrow. The isthmus is the junction between the outer cartilaginous two-thirds of the external canal and the bony inner one-third.

The tympanic membrane (Fig. 4.3) is a translucent membrane visible at the inner extremity of the external canal. In its normal state the membrane appears grey and shiny and through it the handle of the malleus is visible with its inferior pole (the umbo) pointing posteriorly. The umbo can be seen fairly close to the centre of the tympanic membrane. Inferior to the umbo, an arc of light (the light reflex) reflects back to the observer. This arc is directed antero-inferiorly.

Fig. 4.3 Anatomy of normal tympanic membrane.

THE MIDDLE EAR

This extends from the inner surface of the tympanic membrane to the temporal bone and includes the air filled cavities containing the three ossicles (from proximal to distal to the observer these are the malleus, incus and stapes; see Fig. 4.4), the Eustachian tube and the mastoid air cells. The function of the middle ear is to magnify sound-waves sensed by the tympanic membrane and forms an important part of conductive hearing. This magnification of sound is done by the three ossicles, the last of which is the stapes whose foot-plate fits in the oval window which is connected to the cochlea of the inner ear. The function of the Eustachian tube is to aerate the middle ear so that the pressure in the middle ear is equal to the outside pressure (in the external canal) and thus allow the tympanic membrane to vibrate freely.

Fig. 4.4 The auditory ossicles.

There are two important nerves that pass through the medial wall of the middle ear. These are the facial nerve and its off-shoot, the chorda tympani (concerned with taste from the tongue on the same side and with submandibular and sublingual salivary glands). The facial nerve passes in the bone above and behind the stapes footplate, whereas the chorda tympani emerges through the posterior wall of the middle ear and passes between the malleus and incus.

THE INNER EAR

The inner ear is that part of the auditory mechanism within the petrous temporal bone. The inner ear is called the labyrinth and is comprised of the cochlea, vestibule and semi-circular canals. The cochlea is the organ of hearing and the semicircular canals are the organ of balance. The sensorineural part of hearing is located here in the inner ear, whereas conductive hearing is managed by the external and middle parts of the ear. The sensori– part of hearing occurs within the cochlea, whereas the neuro-part occurs within the eighth (VIII) nerve and beyond.

The cochlea records the transmission of sound via hair cells which convert the signal received into electrical impulses. These are transmitted by the auditory (VIII) nerve to the cerebral cortex.

The semicircular canals or balance organ form the peripheral balance organ. There are three canals: the superior, lateral and posterior. The organ is neurologically connected to the eyes and cerebellum. The eyes, proprioception and cerebellum, together with the cerebral cortex, form the central balance control.

Symptoms of diseases of the ear

VISIBLE SYMPTOMS

Patients may present with symptoms of visible external abnormalities. The conditions that may be seen usually present because of concern about the cosmetic appearance of the ear.

PAIN IN THE EAR (OTALGIA)

Pain in the ear may arise from the ear itself (usually unilateral) but may arise from other sources. The cause can usually be determined on history and clinical examination. The possible causes of otalgia are summarised in the differential diagnosis box.

To fully assess causes of otalgia it is necessary to exclude causes of referred pain. The clinician should directly question whether the patient has any problem with other structures such as teeth, the pharynx or cervical spine.

To assess aural causes of the symptom of otalgia, ask about any associated swelling, discharge, deafness, giddiness or vertigo. Any history of excessive contact with water such as by swimming, bathing or showering is relevant and it is wise to check that the patient has not been putting anything into the external canal (cottonwool buds, pins).

DISCHARGING EAR (OTORRHOEA)

The ear naturally discharges wax which is a mixture of skin debris and apocrine gland secretion.

Pathological discharge from the ear varies in nature from watery to foul-smelling or blood-stained. A green-coloured discharge often indicates pseudomonas infection, whereas a blackened discharge may indicate fungal infection.

With foul-smelling discharge, or with the presence of pseudomonas infection, middle ear disease (and therefore a perforated tympanic membrane) should be suspected. In the rare instance of a cerebrospinal fluid (CSF) leak, due to trauma or surgery, the discharge will be watery. A mucoid discharge is suggestive of middle ear disease. Purulent discharge is commonly from infection of the external canal.

A most common cause of a bloodstained discharge is infection, but the rare instance of a squamous cell carcinoma may present with this.

Discharge is often associated with otalgia and the timing of the two symptoms will often indicate the origin. Otalgia from middle ear disease is usually relieved when the tympanic membrane ruptures and discharges mucopus, whereas continuing pain associated with discharge usually indicates external ear inflammation.

HEARING LOSS (DEAFNESS)

Hearing loss is recognised as being either conductive or sensorineural. It varies in degree from minor to profound and affects all age groups. Poor hearing is significant in infants because of the association with slow or abnormal development of speech. Assessment of hearing in infants and young children is difficult (see p. 92). The clinician should take careful note of parents’ concerns. Hearing loss of old age is called presbyacusis. There are many causes of hearing loss.

TINNITUS

Tinnitus is the symptom of noise in the ears. It is difficult to investigate because it is a subjective symptom. It may be heard as a continuous, pulsatile or episodic sound. The sound may be difficult for the patient to describe but is often noted as whistling, buzzing or crackling. The sounds experienced are not complex auditory hallucinations as found in certain psychoses.

The most common cause of tinnitus is the onset of sensorineural deafness associated with degeneration of the cochlea. However, anything which interferes with the hearing mechanism (even wax) may produce tinnitus. All the possible causes of hearing loss should be considered when tinnitus is present. It is one of the triad of symptoms that are observed in Ménière’s disease, the others being vertigo and loss of hearing. Tinnitus may arise from the Eustachian tube, which is also the site of the rare condition of palatal myoclonus.

In present day usage it is unusual to see tinnitus caused by drugs, but it may be seen in the treatment of rheumatic fever by high dose aspirin and is a recognised side-effect of aminoglycosides. High doses of nonsteroidal anti-inflammatory drugs may also induce tinnitus. This form of drug-induced tinnitus is usually reversible on stopping the medication.

A red flag sign is when the tinnitus is unilateral. As with unilateral deafness, an acoustic neuroma must be considered and investigated.

VERTIGO (DIZZINESS)

Vertigo is a symptom of imagined spinning or unsteadiness. The patient feels they or their surroundings are moving. This is true vertigo and is caused by inner ear, vestibular, dysfunction. Vertigo arising from the vestibular mechanism is known as peripheral vertigo.

Examination of the ear

THE AUROSCOPE

Use the largest aural speculum that fits in the external canal comfortably. Hold the auroscope at its point of balance (centre of gravity). Balance it lightly in the hand. Do not grab it like a screwdriver! Use the same hand as the ear (left hand for left ear) (see Fig. 4.5). When inserting the auroscope retract the pinna posteriorly with the free hand (right hand for left ear). This opens the canal for easier inspection. Always examine the pinna before examining the external canal.

Fig. 4.5 How to hold the auroscope.

Do not rush to insert the auroscope and, when inserting it, look at the canal throughout its whole length. Observe for any anatomical abnormality and note the external appearance of any discharge or eczema. The appearance of discharge, if mucoid, may indicate middle ear disease rather than otitis externa, whereas evidence of eczematous skin in the pinna (or psoriasis) may indicate that otitis externa will be found in the canal.

Look also for scars of mastoid surgery (pre- or post-auricular) because passing the auroscope too hastily into the ear may result in a large posterior mastoid cavity being overlooked.

EXTERNAL EAR

Pinna

Minor congenital abnormalities

Bat ears is the term given to ears which do not lie flat against the head but protrude outwards. They occur in about 2% of the population and if to be surgically corrected this is best left until after six years of age.

Pre-auricular sinus is a defect in embryological development and usually occurs antero-superiorly to the tragus (Fig. 4.6).

Fig. 4.6 Site of preauricular sinus.

Accessory auricles occur anterior to the tragus (Fig. 4.7) and are another embryonic fault.

Fig. 4.7 Site of accessory auricles.

Gross congenital deformities are rare and include anotia (complete absence of the pinna). The conditions can occur with normal or abnormal development of the middle and inner ear.

Skin changes

Eczema or psoriasis are common conditions which may involve the pinna and external canal. Like any skin condition, secondary infection is a possible complication and is more likely to occur in the external ear because of the accumulation of debris.

Infection/inflammation can be severe with pain, redness and swelling. The infection may be an extension of infection from the external canal but even if localised to the pinna should be treated with systemic antibiotics. Infections of the pinna include cellulitis and perichondritis, where the underlying cartilage is infected.

Cauliflower ears are the result of previous untreated traumatic haematoma of the pinna. Early surgical treatment of the initial haematoma may prevent lasting deformity.

Chondrodermatitis nodularis helicis is a benign nodular condition usually of the helix of the ear. The aetiology is unknown but, as it occurs in later life, may be related to sun damage. It can only be differentiated from malignant conditions by biopsy.

Basal cell carcinomata and squamous cell carcinomata are tumours most commonly seen on the pinna and require appropriate surgical treatment.

Chondromata arise from cartilage, which forms the outer one-third of the canal. They may vary in size from being quite small to obstructing the whole canal. They rarely need attention but may make it difficult to remove wax and observe the inner part of the canal and the tympanic membrane. To the inexperienced eye chondromata may appear alarming and arouse concern about malignancy. They are swellings that are covered by normal epithelium and vary greatly in size from minor swellings to those obstructing most of the external canal.

External canal

The diameter of the canal is very variable and even in some adults may be very narrow. In a child the canal is straight and the tympanic membrane is easily seen. In adults the distal part of the canal, close to the tympanic membrane, narrows (the isthmus) in its final third and deflects downwards. This results in a recess inferiorly with an acute angle being formed between canal and tympanic membrane. It is thus more difficult to see the whole tympanic membrane and debris or foreign bodies are more easily concealed from the clinician in the recess (see Fig. 4.1).

Wax

Wax is the natural accumulation of skin debris and secreted oil from the apocrine glands of the external canal and unless causing symptoms does not need to be removed. Before full examination of the external canal can be complete, the ear should be cleaned of wax. Wax, impacted or otherwise, is one of the commonest conditions of the ear dealt with by the general physician. It may present with a difficulty in hearing or even with pain.

The production and accumulation of wax (rather than its natural expulsion) is dependent on occupational and genetic factors (gene on chromosome 16). The removal of impacted wax gives the greatest relief (in both hearing and discomfort) to an afflicted patient.

The most common method used to clear wax is by syringing or the now more acceptable irrigation (by an electrical pulsed pump). There are contraindications to syringing.

Review

Contraindications to syringing

• Previous ear surgery – mastoid, tympanoplasty, stapedectomy

• Previous otitis externa

• Perforation

• Tinnitus

• Labyrinthine disturbance

Water in the ears is a common trigger for otitis externa and it is important that the ears are fully cleaned if possible so that no water is trapped behind any remaining wax. The ears should be carefully dried after syringing and it is useful to have an operator trained in the use of a Jobson Horne probe (tipped with cotton wool) to dry the outer part of the external canal. In addition to the Jobson Horne probe, useful instruments for removing wax include a wax hook, crocodile forceps and aural forceps (Fig. 4.8).

Fig. 4.8 Instruments useful in the removal of wax. From left to right: Jobson Horne probe, wax hook, crocodile forceps, aural forceps, aural speculum, aural sucker.

Water used to irrigate wax should be at 37°C (hand temperature). Variation in this temperature may stimulate the labyrinth, causing temporary giddiness.

The ENT specialist will have access to microsuction, which is light suction applied by an aural cannula under operating-microscope vision.

Whatever method is used to clean the external canal, this must be done before any external canal or middle ear disease can be diagnosed.

THE MIDDLE EAR

Tympanic membrane

The whole circumference of the membrane should be visualised. In its normal state the membrane appears grey and shiny and through it the handle of the malleus is visible with its inferior pole (the umbo) pointing posteriorly. Inferior to the umbo, an arc of light reflects back to the observer. This arc is directed antero-inferiorly (Fig. 4.9).

Fig. 4.9 Normal tympanic membrane.

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