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• INNER EAR

Anatomy

• The inner ear is the bony labyrinth, a system of passages comprising two main functional parts: the organ of hearing, or

cochlea the vestibular apparatus,

the organ of balance that consists of three semicircular canals and the vestibule.

There are two compartments of fluid in the cochlea (as well as in the rest of the inner ear):

The perilymphatic space, which is within the bony labyrinth and surrounds the membranous labyrinth

The endolymphatic space, which is within the membranous labyrinth

• Within this ivory hard bone, there are fluid-filled hollows.

• Within the cochlea are three fluid filled spaces:

the tympanic canal the vestibular canal the middle canal

• The eighth cranial nerve comes from the brain stem to enter the inner ear where it also innervates the inner ear.

• When sound strikes the ear drum, the movement is transferred to the footplate of the stapes, which presses into one of the fluid-filled ducts of the cochlea.

• The fluid inside this duct is moved, flowing against the receptor cells of the Organ of Corti, which fire.

• These stimulate the spiral ganglion, which sends information through the auditory portion of the eighth cranial nerve to the brain.

• Hair cells are also the receptor cells involved in balance

• Vestibular hair cells are stimulated by movement of fluid in the semicircular canals and the utricle and saccule.

• Firing of vestibular hair cells stimulates the Vestibular portion of the eighth cranial nerve

• It tells the brain about the attitude, rotation, and linear motion of the head.

Infections

• Infections of the inner ear are usually viral.• Symptoms of bacterial and viral infections may be

similar, the treatments are very different• The onset is usually very sudden, with severe dizziness

developing abruptly during routine daily activities. • In other cases, the symptoms are present upon

awakening in the morning. • After a period of gradual recovery that may last several

weeks, some people are completely free of symptoms. • Others have chronic dizziness, if the virus has damaged

the vestibular nerve.

Neuronitis

• Neuritis is inflammation of the vestibular branch of the vestibulo-cochlear nerve.

• Pathophysiology:

Its etiology remains unknown Vestibular neuronitis appears to be a sudden disruption of

afferent neuronal input from 1 of the 2 vestibular apparatuses. This imbalance in vestibular neurologic input to the central

nervous system (CNS) causes symptoms of vertigo.  At least some cases are thought to be due to reactivation of

latent herpes simplex virus type 1 in the vestibular ganglia.

Neuronitis

• Clinical Presentations:Dizziness Vertigo No change in hearingNauseaVomitingUnsteadiness and imbalanceDifficulty with visionImpaired concentration

Labyrinthitis

• Labyrinthitis is inflammation of the labyrinth,occurs when an infection affects both branches of the nerve.

Labyrinthitis

• Clinical Presentation:Hearing changes Dizziness VertigoNauseaVomitingUnsteadiness and imbalanceDifficulty with vision Impaired concentrationTinnitus

Meniere’s Disease

• Is a disorder of the inner ear that can affect hearing and balance.

• Etiology Unknown

• Pathology Excessive accumulation of

endolymphatic fluid (hydrops)

The distension of the endolymphatic compartment may rupture the Reissner’s membrane

Meniere’s Disease

• This leads to mixing of the endolymph and the perilymph

Normal membranous labyrinth Dilated membranous labyrinth in Meniere's disease (Hydrops)

Meniere’s Disease

• Symptoms• Triad of symptoms:

Intermittent attacks of vertigo- lasting 30mins -6hrs accompanied by nausea and vomiting

A fluctuating sensorineural hearing loss- typically affects the lower frequencies

Tinnitus

• Pt. has a sensation of pressure in the affected ear before attack

Meniere’s Disease• A particularly disabling symptom is a sudden

fall typically occurring without warning. • These falls are called "otolithic crisis of

Tumarkin“• They are attributed to sudden mechanical

deformation of the otolith organs (utricle and saccule), causing a sudden activation of vestibular reflexes.

• Patients suddenly feel that they are tilted or falling (although they may be straight), and bring about much of the rapid repositioning themselves.

• This is a very disabling symptom as it occurs without warning and can result in severe injury.

• Treatment: labyrinthectomy vestibular nerve section

a very dangerous variant of Meniere's disease, which can result in abrupt falls.

Meniere’s Disease

• Investigations Pure tone audiometryElectrocochleography MRI- role out Acoustic neuroma

• Treatment:BetahistadineDiureticsSelective destruction of the labyrinth by percolating

gentamicin through a grommrt

Acoustic Neuromas

• Is a benign primary intracranial tumor of the myelin-forming (schwann) cells of the vestibulocochlear nerve (CN VIII).

• It is a schwannoma because it affects the vestibular portion of the VIIIth CN

• Pathogenesis – Occurs: Sporadically Hereditary as part of von Recklinhausen neurofibromatosis, in which case the

neuroma may take on one of two forms:

In Neurofibromatosis type I, a schwannoma may sporadically involve the 8th nerve, usually in adult life, but may involve any other cranial nerve or the spinal root. Bilateral acoustic neuromas are rare in this type.

In Neurofibromatosis type II, bilateral acoustic neuromas are the hallmark and typically present before the age of 21. These tumors tend to involve the entire extent of the nerve and show a strong autosomal dominant inheritance. Incidence is about 5 to 10%.

Acoustic Neuroma

• As the tumor grows, it usually extends into the posterior fossa to occupy the angle between the cerebellum and the pons (cerebellopontine angle). Because of its position, it may also compress the 5th, 7th, and less often, the 9th and 10th cranial nerves.

• Later, it may compress the pons and lateral medulla, causing obstruction of the CSF and increased intracranial pressure.

• Symptoms Unilateral sensorineural hearing loss Unilateral tinnitus Both Vertigo (20% of cases Numbness of face (large tumours)

Acoustic Neuromas

• InvestigationMRI

• TreatmentSurgical resection‘wait and see’ policy (elderly & minimal

symptoms)Stereotactic radiotherapy (small tumours)