Conditions of the Inner ear (Tab 40.3)
Congenital
Congenital inner ear disorders may be
associated with external or middle ear abnormalities or exist on their own.
The most common anomaly is dysplasia of the membranous labyrinth, although
dysplasia of the bony labyrinth and even total aplasia of the ear may occur.
Intrauterine infections, including rubella, toxoplasmosis and cytomegalovirus,
can cause inner ear damage. Perinatal hypoxia, jaundice and prematurity are
also risk factors for a hearing loss. After birth, meningitis may cause profound
sensorineural hearing loss.
If
a child’s parents suspect a hearing impairment it is important to believe
them, especially when glue ear has been excluded. In children in whom there is a
suspicion of sensorineural hearing loss, brainstem evoked audiometry is used
to establish hearing thresholds (Fig. 40.23). If some hearing is present, the
early fitment of hearing aids can maximise the neural plasticity that is present
in the developing brain. If a child has a profound hearing loss, then early
intervention with a cochlea implant may he appropriate (Fig.
40.24). Most cases
of profound sensorineural hearing loss are due to loss of cochlear hair cells so that an
implant inserted through the round window can selectively stimulate the cochlear
neurons which usually remain intact.
Degenerative
Presbyacusis, a degenerative disorder, is a
term used to describe the hearing loss of old age. It is characterised by a
gradual loss of hearing in both ears, with or without tinnitus. The hearing loss
usually affects the higher frequencies and a classical audiogram is shown in
Fig. 40.25.
The consonants of speech lie within the
high-frequency range which makes speech discrimination difficult. Examination of
an elderly person s cochlea shows loss of hair cells, particularly at the basal
turn of the cochlea. With ageing the dynamic range of hearing is also reduced so
that elderly people often find loud noises uncomfortable. This phenomenon is
known as ‘recruitment’.
Many
patients with presbycusis are concerned that they may lose their hearing
completely and need reassurance. Hearing aid technology has improved
dramatically and most patients now benefit (Fig. 40.26). Care and attention to
detail when fitting the hearing aid are essential, together with monitoring the
patient’s progress. If this does not occur the hearing aid ends up in the
bedroom drawer.
Tinnitus describes an abnormal noise that appears to come from the ear or within
the head. It may have an extrinsic cause, for example the pulsatile tinnitus of
a glomus jugularae tumour. Usually, however, the tinnitus is generated within
the cochlea, and most people will experience tinnitus at some time in their
life.
Tinnitus frequently accompanies presbycusis, as
well as any condition that damages the inner ear structures. Most individuals
adapt to the presence of tinnitus but in some patients it proves intrusive.
Reassurance
Trauma
Trauma to the inner ear can be caused by noise
or direct injury. Hair cells within the cochlea are damaged by sudden acoustic
trauma (blast injury or gun fire) or by prolonged exposure to excessive noise.
The sensorineural hearing loss that results is greatest at high frequencies
(particularly 4000 Hz) and is often accompanied by tinnitus (Fig.
40.28). The
law in the UK requires that workers are protected from noise, but in a disco an
individual relies on common sense!
The
otic capsule is the hardest bone in the body but if trauma to the head is severe
temporal bone fractures may occur. These tend to be either longitudinal (80 per
cent) or transverse (20 per cent). Transverse fractures usually involve the
labyrinth and lead to a sensorineural hearing loss which is permanent. Profound
vertigo occurs initially followed by gradual compensation. In about 50 per cent
of cases there is an associated facial nerve paralysis.
Facial paralysis
•
Think complete or partial
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Protect the eye
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Otoneurological examination to find cause
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Early treatment with steroids and/or antiviral therapy dependent on
aetiology
Drug
ototoxicity is a form of trauma that may damage the inner ear. Some drugs
differentially affect the cochlea causing hearing loss and tinnitus while others
pick out the vestibular system causing vertigo. Aminoglycocides are well known
to be ototoxic, as is cisplatinum. Recognition of risk factors,
such as poor renal function in patients being
treated with aminoglycocides, is most important. Although many topical ear drops
contain aminoglycocides, there is little evidence that such topical treatment
causes sensorineural hearing loss if used for short periods.
Benign
paroxysmal positional vertigo (BPPV) may follow head or neck trauma. Vertigo is
an illusion of movement and BPPV is characterised by intermittent attacks of
vertigo that occur when the head is moved in a certain position. Typically the
vertigo only lasts for a few seconds and is not associated with other otological
symptoms. Positional testing can evoke nystagmus and helps in the diagnosis of
this condition. The condition is usually self-limiting and special manoeuvres
described by Epley help the majority of patients (Fig.
40.29).
Vascular
occlusion
A reduction in labyninthine blood flow with
associated hypoxia is the most likely cause for most cases of sudden onset of
severe sensorineural hearing loss. All patients with a sudden sensorineural
hearing loss should be referred immediately for specialist treatment. The
treatment consists of bed rest, steroids and, in some centres, the
administration of Carbogen (an oxygen and carbon dioxide mixture). Five per cent
of acoustic neuromas present with a sudden sensorineural hearing loss and
therefore radiological investigation, preferably with magnetic resonance
imaging (MRI), is required to exclude this tumour.
Inflammatory
disorders
Inflammation caused by a viral infection is
thought to account for acute vestibular failure (vestibular neuroritis). This
condition is characterised by a sudden onset of vertigo. The vertigo is so
severe that the patient often takes to his or her bed for between 2 and 5
days. Central compensation then occurs, although recurring episodes of
vertigo for up to 18 months can occur. This is thought to be due to incomplete
compensation for the original vestibular damage.
The
aetiology of Ménière’s disease is
not known. The condition is characterised by a triad of symptoms. Intermittent
attacks of vertigo, a fluctuating sensorineural hearing loss and tinnitus. The
patient often has a sensation of pressure in the affected ear before an attack.
The hearing loss typically affects the lower frequencies and is virtually the
only type of sensorineural hearing loss that fluctuates. The time-course of the
vertigo characteristically lasts between 30 minutes and 6 hours. It is often
accompanied by nausea and vomiting. Although the cause of the condition is
unknown, the pathology is well documented. There is an excessive accumulation
of endolymphatic fluid (hydrops) and it is thought that the distension of the
endolymphatic compartment may rupture Reissner’s membrane which leads to
mixing of endolymph and perilymph. This is the basis for the cochlear—vestibular
failure which characterises the condition. The investigations include puretone
audiometry, electrocochleography and MRI scan if available. The latter is
required to exclude an acoustic neuroma which may mimic the symptoms of Ménière’s
disease.
Viral
infections that involve the facial nerve are possibly one of the commonest
causes of facial weakness (80 per cent). Bell’s
palsy results from a viral infection of the facial nerve. The nerve swells
and is compressed in its labyninthine portion as it passes from the internal
auditory meatus towards the middle ear. If the patient presents within the first
48 hours, treatment with high-dose steroids is appropriate. Not all facial nerve
palsies are due to viral infection and a thorough otoneurological examination is
required. The facial nerve can be damaged within the brainstem at the
cerebellopontine angle, within the internal auditory meatus, within the middle
ear, at the skull base and within the parotid. It is essential to consider these
potential sites of facial nerve damage in any patient with VIIth nerve
paralysis.
Ramsey Hunt’s syndrome is caused by herpes zoster virus. It is characterised
by a facial palsy and is often associated with facial pain and the appearance of
vesicles on the ear drum, ear canal and pinna (Fig.
40.30). Vertigo and sensorineural
hearing loss (VIIIth nerve) accompany it. Treatment with aciclovir is effective
if given early.
Metabolic
causes
The metabolic causes of inner ear damage
include diabetes mellitus and thyroid disease, both of which may cause
sensorineural hearing loss.
Neoplasms
Tumours of the inner ear are uncommon but can
present with sensorineural hearing loss, tinnitus and vertigo. Acoustic
neuromas,
which are actually Schwannomas of the vestibular division of the VIIIth nerve,
are the most common, followed by meningiomas. Acoustic neuromas grow slowly and
somewhat unpredictably and as they expand can cause cranial nerve palsies,
brainstem compression and raised intracranial pressure. The early symptoms are a
unilateral sensorineural hearing loss or unilateral tinnitus, or both. It is
important to diagnose these tumours early and remove them when they are small.
The morbidity and mortality from surgery is directly related to tumour size.
If the tumour is removed when
The
investigation of choice for detecting acoustic neuromas is MRI (Fig.
40.31).
In many centres patients with any unilateral otological symptoms are screened
using MRI. If MRI is not available, CT scanning is the next best diagnostic
tool. Occasionally, in an elderly patient, ‘a wait and see’ policy may be
adopted. In such patients repeat MRIs can be used to monitor the tumour.
The inner ear
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Unilateral tinnitus or sudden sensory neural hearing loss needs to be
investigated for possible acoustic neuroma
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Sudden sensory neural hearing loss needs immediate treatment