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 and relaxation therapy are highly effective, as is a hearing aid for patients who also have presbycusis. An ENT surgeon who was a keen fisherman found that he could not hear his tinnitus when fishing next to a waterfall. From this observation tinnitus maskers have been developed (Fig. 40.27). A masker provides a similar noise to the tinnitus and ‘blanks it Out.

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. When assessing a severely injured patient, it is important to record the facial nerve function and, in particular, whether any facial weakness is partial or total. Total facial paralysis immediately following a head trauma suggests a major injury to the nerve and under certain circumstances exploration of the facial nerve to decompress it or repair it may be appropriate. Longitudinal fractures usually spare the labyrinth but frequently involve the external meatus and roof of the middle ear. Important physical findings that may accompany a skull base fracture include a haematoma over the mastoid bone (Battle’s sign), blood in the external ear or a laceration along the roof of the external canal. Cerebrospinal fluid (CSF) otorrhoea or CSF rhinorrhoea (if the tympanic membrane is intact) may occur. A conductive hearing loss may be present because of fluid in the middle ear or disruption of the ossicular chair. A high-resolution CT scan is required to assess skull base fractures.

Facial paralysis

Think complete or partial

Protect the eye

Otoneurological examination to find cause

Early treatment with steroids and/or antiviral therapy dependent on aetiology Barotrauma is a rare cause of a sudden sensorineural hearing loss (SNHL) or acute vestibular disturbance. Rapid changes in pressure across the labyrinthine membranes may occur with diving or flying and may allow air to be forced into the cochlea. Any individual with a sudden sensorineural hearing loss requires urgent hospital admission, and in those with a history of barotrauma it may be appropriate to raise the tympanic membrane and to search for a leak of pen-lymph in the region of the oval or round window.

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 it is small, there is an extremely good chance of preserving facial nerve function.

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. There are three main surgical approaches for resecting acoustic neuromas. A temporal craniotomy and a direct middle fossa approach is used for small tumours only. The translabyrinthine approach is entirely through the ear and does not breach the dura. The neurosurgeon and ENT surgeon work together. There is minimal disturbance to the patient, although the hearing is completely destroyed. A suboccipital approach is performed by a neurosurgeon doing a craniotomy with the ENT surgeon removing bone at the internal auditory meatus. Traction on the cerebellum is required. This increases the morbidity. In some cases, however, what remains of the hearing can be preserved using this approach. The physiological monitoring of the facial nerve and auditory nerve during surgery has improved acoustic nerve surgery results

The inner ear

  Presbycusis: bilateral high-frequency loss

 •  Unilateral tinnitus or sudden sensory neural hearing loss needs to be investigated for possible acoustic neuroma

 • Sudden sensory neural hearing loss needs immediate treatment