Vestibulocochlear nerve disorders

Vestibulocochlear nerve disorders are closely linked to diseases of the inner ear, since it is the inner ear that is affected by this nerve. It is a nerve which is also called the 8th cranial nerve or the statoacoustic nerve and it is a sensory nerve bringing information to the brain from two different organs, namely the ear, namely the organ of Corti of the inner ear, and the organ of balance, namely the vestibular apparatus. Thus, disturbances in this nerve are manifested by different symptoms.

Because the positional auditory nerve involves two nerve types and fibres, most diseases of the positional auditory nerve are manifested by hearing impairment and auditory murmurs, but also by problems with maintaining balance, dizziness and sometimes severe and uncontrollable vertigo. This double nerve begins just around the inner ear, where the auditory fibres converge from the sensory cells of the organ of Corti and the balance fibres from the cells of the Vestibular apparatus.

The two nerve fibres then enter together into the space between the bridge and the cerebellum in the brain and terminate in the brain centre responsible for processing stimuli about position and hearing. Diseases of the statoacoustic nerve, however, do not only affect the nerve itself, which may be affected by various inflammations, tumours or other disturbances of function or signal transmission, but also include diseases related to the organ of Corti and the inner ear, and diseases of the Vestibular Apparatus and Vestibular Function.

Structure of the statoacoustic nerve and signal transmission

The statoacoustic nerve is located in the inner ear, although from the point of view of diseases it is a separate organ that does not necessarily have a connection with other parts of the inner ear. This nerve transmits two types of signals, namely, a signal regarding balance and body position and an auditory signal. The nerve is thus made up of two different fibres, making it unique among other nerves in the body because it can transmit two kinds of signals which it receives from two different organs in the ear.

The first organ is the Organ of Corti, in which the auditory nerve branches. This organ is a set of structures in the septum of the cochlea of the inner ear. Within the auditory receptors, the most important part of the organ are the hair cells, which provide the conversion of the mechanical energy of sound waves into electrical signals. The transmitter then relays this signal from the organ of Corti to the auditory nerve fibres within the 8th cranial nerve, or positionally the auditory nerve.

When an acoustic wave is introduced into the space of the inner ear, mechanical energy is transferred to the basilar membrane, which vibrates. The oscillation in a particular part of the basilar membrane depends on the frequency of the acoustic wave. In each case, this oscillation is picked up by hair cells, which convert it into a nerve impulse for the nerve, which sends it to the brain for further processing. In the case of a disorder of the organ of Corti, there is a problem with the generation or transmission of this impulse to the nerve.

The second organ is the vestibular system. This is a sensory organ located in the labyrinth of the inner ear, which is responsible for the perception of the balance of the body. This apparatus is also the main part of the inner ear and is made up of a system of several canals, which are filled with endolymph inside and perilymph around. In each part there are also sensory neuromast cells that can detect a particular position or balance and pass this information on.

The vestibular apparatus itself consists of the globular sac, the vestibulum as the centre of the apparatus, the ovate sac, the lateral canal, the posterior canal and the anterior canal. These semicircular canals perceive the angular acceleration of the head, while the globular vesicle perceives the rectilinear vertical acceleration and the ovoid vesicle, in turn, the rectilinear horizontal acceleration. This whole apparatus conducts information about the position of the body to the brain, while both the external and internal sap also assist the sensory cells in the apparatus with the conduction of this signal.

Information from both the organ of Corti and the vestibular apparatus is carried by the statoacoustic nerve to the cerebellum, where it is evaluated, but also to other areas of the central nervous system. The analysers themselves are also located in the temporal lobe and are auditory and positional analysers. The nerve itself has several different pathways, each of which conducts information to a different area or part of the brain and nervous system, thus providing the various functions of maintaining position, coordinating movements and perceiving hearing.

If there are disorders in either the auditory or balance organs, or if the problem is directly with the positional auditory nerve, these disorders will manifest themselves as either hearing or balance disorders. Common symptoms thus include hearing loss, partial or complete hearing loss, tinnitus, various ear murmurs, rotational or positional vertigo, dizziness, vertigo, nausea, eye nystagmus or a general balance disorder called vestibular ataxia.

Vestibular function disorders

Disorders and diseases of vestibular function, or vestibular disorders, include, for example, Meniere's disease, labyrinthine hydrops, Meniere's syndrome, benign paroxysmal positional Vertigo, vestibular neuronitis, Lermoyez syndrome, central positional nystagmus, and aural, peripheral, or otogenic Vertigo. All of these disorders and diseases are manifested mainly by disturbances in balance and coordination of balance function and also by vertigo or dizziness.

Vestibular disorders include, for example, Lermoyez syndrome, which manifests itself in frequent and recurrent attacks or episodes of vertigo, with a return to normal perception of balance and movement after the symptom has resolved. Usually, these vertigo episodes are also accompanied by tinnitus and a decrease in hearing function. This syndrome arises from a disturbance directly in the labyrinth, and it is not a chronic disorder that leaves lasting effects.

A relatively common disease is also called vestibular syndrome. It occurs when there is a disturbance of the mutual balance of the two Vestibular apparatuses in both ears. Most often this disease manifests itself like other similar disorders of vestibular function by dizziness and vertigo, which have a rotational character, but also by nausea, vomiting, the person is pale and sweats excessively. The disease occurs due to a conflict of individual sensory inputs to the brain.

This syndrome can take two forms, either peripheral or central. The central one, unlike the peripheral one, is not dependent on the position of the head and manifests itself in a more unpleasant type of dizziness that is permanent. Peripheral vestibular syndrome, in turn, is related to a disturbance in the 1st vestibular nerve pathway, either in the area of the direct receptors of the apparatus or in the area of the ganglia of the vestibular nerve. Unfortunately, in many cases treatment is only symptomatic and not causal.

Benign paroxysmal positional vertigo, abbreviated as BPPV, is a very common disease also caused by the Vestibular apparatus. The cause of the disease is the accumulation of tiny crystals in a certain part of the otic canals in the apparatus, which cause irritation of the hair cells. The disease is manifested by intense but short-lived dizziness and is most common in people over 50 years of age after an accident. Treatment consists of a series of various exercises and regenerative exercises.

Vertigo is also quite common and can take several forms, such as peripheral, otogenic or aural. This is the so-called true vertigo, when a person experiences the illusion of movement, either linear or rotational. Most often, this condition is caused by dysfunction of the peripheral or central nervous system. Usually this condition is also accompanied by vomiting, pallor and general malaise. Vertigo can be of centralor peripheral origin, if the involvement is bilateral, vestibular ataxia and oscilloscopy also occur.

Cranial Nerve VIII disorders

The vestibular nerve can be affected by several types of diseases. Whether it is directly inflammatory diseases, or tumors or other diseases causing impaired functionality or the possibility of nerve signal transmission from the positional-auditory apparatus to the brain. Most commonly, however, diseases affecting or relating to the cranial nerve include various types of inflammation of an infectious nature or various tumours causing oppression and impairment of the nerve's functionality.

Vestibular neuronitis is an inflammatory disease that is isolated and unilateral and affects the vestibular nerve. It is an inflammation of the vestibular nerve and is manifested by dizziness and is most commonly caused by a viral infection. It often affects people under the age of 40 years, there is no hearing loss, but rotational vertigo of an acute or subacute nature occurs. In complete vestibular syndrome, tonic deviations and complete nystagmus, i.e. uncontrollable repetitive minor eye movements, also occur.

The disease can take both static and dynamic forms, depending on which characteristic of signs and clinical symptoms prevails in the person affected by this neuritis. The treatment of the disease is conservative and antiviral drugs are used for a long time, usually up to 3 weeks. Rehabilitation is also important once the vegetative symptoms have passed and movement is possible. Unfortunately, however, in many cases the disease causes long-term problems even after cure, and complete functional recovery occurs in only a third of cases.

Neurinoma of the nervoacoustic nerve is a relatively common disease of this important nerve, and it is a tumour of a benign nature that develops over a relatively long period of time, and the tumour sometimes grows for several years. The tumour presses on the nerve, causing a gradual progression of symptoms, particularly problems with walking and maintaining balance, but there are also problems with hearing as the tumour affects both nerve fibres. Treatment consists of radiological removal of the tumour with a gamma knife. The success rate of the operation is relatively high, but if the tumour is diagnosed late, it is usually no longer possible to restore the auditory function of the nerve.

Neurofibromatosis of the positional auditory nerve is a disease in which there is a pathological multiplication of the supporting cells of the nervous system, thereby also forming a benign tumor near the nerve. At the same time, it is often a precursor of other cancers, which corresponds to the typical symptom accompanying the disease, when smaller tumours appear on different parts of the body at the end of the nerve. However, these tumours are also benign. In this case, the disease must also be treated surgically by removing the clusters of these cells.