Inner Ear: Anatomy, Function & Diseases

Q: Benign paroxysmal positional vertigo

It is caused by the movement of otoliths that for unknown reasons detach from their natural location and either affect the dome (cupolithiasis) or are free in the endolymph (canalithiasis). Benign paroxysmal positional vertigo (BPPV) alone accounts for about 20 per cent of all vertigo. The diagnosis of paroxysmal positional vertigo is made by the ENT specialist or audiologist through special diagnostic manoeuvres. The treatment involves an otolithic repositioning procedure called liberating manoeuvres.

Q: Méniere's disease

It manifests itself with periodic vertiginous crises, tinnitus, fullness (feeling of a 'closed' ear) and reduced hearing capacity in the affected ear (fluctuating hearing loss). Generally, the vertiginous crisis manifests itself with objective vertigo, nausea and vomiting. It affects around 0.2 % of the population and is most common between the ages of 20 and 60. The cause of the disease is unknown, but is linked to endolymphatic hydrops with consequent dilatation of the membranous labyrinth that triggers the crisis. The diagnosis of Méniere's disease is clinical, made on the basis of the medical history and the data obtained from the audiometric and otoneurological examination. Other tests such as MRI of the brain are used to rule out other central pathologies. Treatment is essentially medical.

What is the inner ear?

The ear is a complex organ and is composed of three parts: the outer ear (i.e. the visible portion and ear canal), the middle ear (which contains, behind the eardrum, the three tiniest bones within the human body) and the inner ear (which occupies a small cavity within the temporal bones, contributing to the structure of the skull).

Anatomy

The inner ear has a complex structure: it is made up of the bony labyrinth (a system of cavities excavated in the thickness of the temporal bone) and the membranous labyrinth, which are separated from each other by the perilymphatic space (a complex of interconnecting fissures in which a liquid, the perilymph, is contained). The bony labyrinth is made up of a vestibular part (posterior) comprising the vestibule, the bony semicircular canals and the vestibule aqueduct, and an acoustic part (anterior) consisting of the cochlea or bony cochlea and the cochlea aqueduct. The membranous labyrinth appears as a set of hollow organs, containing a fluid - endolymph - communicating with each other, bounded by a membranous wall.

The membranous labyrinth consists of:

Three semicircular canals: posterior, superior and lateral.
Utricle: a vesicular organ with an ovoid shape.
Sacculus: smaller than the utricle and located below it.
Endolymphatic sac: connected to the sacculus and utricle by the endolymphatic duct and canal.
Cochlea or membranous cochlea

What does the inner ear do?

The vestibular system is responsible for balance. The neurosensory structures are located at the level of the utricle, the sacculus and the semicircular canals where the balance sensory cells are located, equipped with vertical cilia, on which rests a layer of calcium oxalate crystals called otoliths.

A woman with her left hand resting on the headphones during a hearing test

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Diseases of the inner ear

The main symptomatic feature of diseases affecting the labyrinth is the occurrence of vertigo, defined as a false sensation of movement of the body or surroundings. Among the types of vertigo we distinguish:

Benign paroxysmal positional vertigo

It is caused by the movement of otoliths that for unknown reasons detach from their natural location and either affect the dome (cupolithiasis) or are free in the endolymph (canalithiasis). Benign paroxysmal positional vertigo (BPPV) alone accounts for about 20 per cent of all vertigo. The diagnosis of paroxysmal positional vertigo is made by the ENT specialist or audiologist through special diagnostic manoeuvres. The treatment involves an otolithic repositioning procedure called liberating manoeuvres.

Méniere's disease

It manifests itself with periodic vertiginous crises, tinnitus, fullness (feeling of a 'closed' ear) and reduced hearing capacity in the affected ear (fluctuating hearing loss). Generally, the vertiginous crisis manifests itself with objective vertigo, nausea and vomiting. It affects around 0.2 % of the population and is most common between the ages of 20 and 60. The cause of the disease is unknown, but is linked to endolymphatic hydrops with consequent dilatation of the membranous labyrinth that triggers the crisis. The diagnosis of Méniere's disease is clinical, made on the basis of the medical history and the data obtained from the audiometric and otoneurological examination. Other tests such as MRI of the brain are used to rule out other central pathologies. Treatment is essentially medical.

Vestibular neuritis

Vestibular neuritis is caused by an acute deficit of the vestibular nerve on one side that causes the onset of sudden vertiginous symptoms, always accompanied by nausea, vomiting, cold sweating and tachycardia. The aetiology is uncertain, but the main event is probably due to inflammatory phenomena sustained by viruses. Therapy relies on the use of drugs and vestibular rehabilitation.

Vestibular migraine

It is always to be suspected when in the presence of vertigo there is also a clinical history of migraine. It is one of the most common causes of episodic vertigo among children. Among adults, it is three times more common among women and frequently occurs between the ages of 20 and 50. Medical therapy involves the use of anti-emergency drugs in combination with symptomatic drugs.

Vascular vertigo

It is linked to damage to the peripheral and/or central vestibular system attributable to a deficit in the circulation of the labyrinthine terminal microcirculation. Vertigo is frequently associated with neurological signs and symptoms such as double or altered vision, headache and fatigue.

Other causes of vertigo

Other pathologies of neoplastic or degenerative origin (Meningiomas, Schwannomas, Ependymomas, Gliomas, Medulloblastomas, Neurofibromatosis, etc.) can also cause episodic vertigo or feelings of instability.

Viral causes such as herpes zoster or bacterial (purulent labyrinthitis) can trigger vertigo. Usually fever occurs first, only in bacterial forms, and then vertigo with hearing loss and, often, tinnitus. Treatment is aetiological.

Drug-induced vertigo and/or dizziness, without any other cause, accounts for about 23% of cases of dizziness in the elderly. The use of five or more drugs is associated with an increased risk of dizziness and subsequent fall. Older patients are particularly susceptible to adverse drug effects due to age-related pharmacokinetic and pharmacodynamic changes.

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Inner ear