EIGHTH CRANIAL NERVE

From Big Medical Encyclopedia

EIGHTH CRANIAL NERVE [nervus vestibulocochlearis, n. octavus (PNA), n. statoacusticus (JNA), n. acusticus (BNA); synonym: vestibulo-cochlear nerve, acoustical nerve, equilibrium and acoustical nerve] — VIII couple of cranial nerves. Most often in clinic the term «acoustical nerve» is used.

Anatomy

In P. - at. N distinguish two parts: predoor part, pl nerve of a threshold, static nerve (pars vestibularis) and cochlear part, or acoustical nerve (pars cochlearis). Predoor part P. - at. the N bears information from the afferent terminations located in semicircular channels, an elliptic sack (utricle) and spherical sack (see. Vestibular analyzer , Inner ear , Otolitovy device ). Cochlear part P. - at. the N carries out an impulse from spiral body (see. Kortiyev body ).

Fig. 1. Diagrammatic representation of a webby labyrinth and eighth cranial nerve: 1 — the Eighth cranial nerve, 2 — a predoor part, 3 — a facial nerve, 4 — elliptic meshotchaty a nerve, 5 — a lateral ampullar nerve, 6 — a front ampullar nerve, 7 — a back ampullar nerve, 8 — a spherical sack, 9 — spherically-meshotchaty a nerve, 10 — a preddverny node, 11 — a cochlear part.
Fig. 2. The diagrammatic representation of an arrangement of nerves in internal acoustical pass (a part of a posterosuperior wall of internal acoustical pass is removed): 1 — an outside opening of a water supply system of a threshold, 2 — spherically-meshotchaty a nerve, 3 — a preddverny node, 4 — a predoor part, 5 — a cochlear part, 6 — an intermediate nerve, 7 — a facial nerve, 8 — internal acoustical pass, 9 — elliptic meshotchaty a nerve.

Predoor part The item - at. the N (fig. 1) has the preddverny node (gangl, vestibulare) lying in internal acoustical pass. In an ireddverny node distinguish two parts: upper (pars superior) and lower (pars inferior). Peripheral shoots of bipolar cells of an upper part of a predoor node go to receptor fields — a spot of an elliptic sack (macula utriculi) and ampullar combs of front and lateral semicircular channels — and create elliptic meshotcha - that-ampullar nerve (n. utriculoam-pullaris), elliptic meshotchaty a nerve (and. utricularis), front and lateral ampullar nerves (nn. ampul lares anterior et lateralis). Peripheral shoots of cells of the bottom of a predoor node are distributed in a spot of a spherical sack (macula sacculi) and an ampullar comb of the back semicircular channel, forming spherically-meshotchaty nerve (n. saccuiaris) and a back ampullar nerve (n. ampullaris posterior). The central shoots of cells of a predoor node form a predoor part (pars vestibularis), edges in internal acoustical pass connects to a cochlear part (pars cochlearis) and creates P. - at. N. In internal acoustical pass the nerve is located together with facial and intermediate nerves (fig. 2), and then enters a head cavity through an internal acoustical opening. In the area mostomozzhechkovy corner (see) a nerve enters a brain trunk two roots — pre-door (upper) and cochlear (lower). A predoor part of a nerve at the level of the vestibular field of a rhomboid pole comes to an end in the following kernels: upper — nucleus vestibularis superior (Bekhterev's kernel), medial — nucleus vestibularis medialis (Shvalbe's kernel), lateral — nucleus vestibularis lateralis (Deyters's kernel) and lower — nucleus vestibularis inferior.

Cochlear part The item - at. the N begins from a spiral node (the first neuron of the acoustical way) lying in the spiral channel of a core of a snail. Peripheral shoots of cells of a node reach spiral body. The central shoots, passing a core of a snail through openings of the made a hole spiral way, get into internal acoustical pass where create cochlear part P. - at. N. The last together with predoor part P. - u.n. enters a head cavity through an internal acoustical opening, going to a brainstem. In the field of a mostomozzhechkovy corner cochlear part P. - at. the N is included into a brain trunk, coming to an end in dorsal and ventral kernels (front and back cochlear kernels, T.) — see. Acoustic analyzer , Acoustical centers, ways .

Methods of a research

the Functional condition of P. - at. the N is defined at a complex research of acoustical and vestibular analyzers (see. Audiometriya , Vestibulometriya ). Vestibulo-metrichesky, audiological and from - neurologic methods of a research allow to differentiate P.'s defeat - at. N within an inner ear or its root in internal acoustical pass and a mostomozzhechkovy corner. At tonic diagnosis the possibility of involvement in process of V, VI, by VII, IX, X craniocereberal is considered (cranial, T.) nerves, topographical integrated with an eighth cranial nerve.

Pathology

Symptoms of defeat of predoor part P. - at. N are dizziness (see), disturbance of stability at rest and at the movement, nystagmus (see), and also vegetative reactions — nausea, vomiting, change of a respiratory rhythm, pulse and ABP (see. Vestibular symptom complex ). Defeat of cochlear part P. - at. the N is shown by noise in ears (see) and disorder of hearing up to full deafness as disturbance of sound perception (see. Relative deafness , Deafness ). At defeat of both parts of a nerve all symptoms are shown at the same time and are expressed to a greater or lesser extent. In a wedge, practice this complex of symptoms is called a peripheral kokhleovesti-bulyarny syndrome. Depending on extent of manifestation of a syndrome it is possible to judge excitement, oppression or loss of function P. - at. N.

P.'s defeat - at. the N can be caused inf. diseases (flu, shingles, epidemic parotitis, typhus, measles, scarlet fever, malaria, tuberculosis, syphilis, etc.); diseases of cardiovascular system; intoxications antibiotics of an aminoglikozidny row and other pharmaceuticals, and also chemical substances. Dysfunction of P. - at. the N is observed at labyrinthites (see), an arachnoiditis of a mostomozzhechkovy corner (see. Arachnoiditis ), Menyer's diseases (see. Menyera disease ), tumors of facial and preddverno-cochlear nerves, at the centers of an otosclerosis with distribution to internal acoustical pass (see. Otosclerosis ), at an injury of a pyramid of a temporal bone and skull. P.'s damage - at. the N can be connected with noise and vibration, and also with short-term powerful sounds — a shot, explosion (see. Acoustic injury , Vibrotrauma ). Disturbing factors can selectively affect this or that part of a nerve or a nerve in general. In certain cases inertly current inflammation of P. - at. N symptoms of defeat of a predoor part are not shown and into the forefront symptoms of defeat of a cochlear part act. All this gives the grounds at full or partial defeat of P. - at. N on an equal basis with the term «neuritis of an eighth cranial nerve» to use the terms «neuritis of an acoustical nerve» or «cochlear neuritis». Due to the rarity of the isolated defeat of predoor part P. - at. the N the term «vestibular neuritis» did not find a wide spread occurance as well as the term «vestibular neurocyte» in spite of the fact that this term is meant as a certain clinic of vestibular frustration without subjective and objective hearing disorder and characterized by the heavy attacks of dizziness which are followed by vomiting, disorder of balance, a spontaneous nystagmus.

At P.'s defeat - at. N carry out the complex treatment directed to a basic disease and recovery of function of a nerve. Terms of an initiation of treatment since it is effective in initial stages of defeat have essential value. Symptomatic therapy at P.'s inflammation - at. the N includes antiinflammatory treatment, dehydration, desintoxication, desensitization. Use the drugs improving blood circulation, processes of fabric exchange and regulating synoptic transfer. Are reasonable hyperbaric oxygenation (see) and reflexotherapy (see).

The forecast is favorable if the intensive care is begun at early stages of defeat of P. - at. N, on condition of the found-out etiology. Permanent functional disturbance of an eighth cranial nerve is most characteristic of virus defeat.

P.'s injuries - at. N are shown by symptoms of disturbance of functions of predoor and cochlear its parts. Expressiveness of these symptoms depends on weight of damage. At defeat of predoor part P. - at. N are characteristic a spontaneous vestibular nystagmus, disturbance of a statics, coordination and gait. At defeat of cochlear part P. - at. the N is observed unilateral noise in an ear, relative deafness or deafness. Because together with P. - at. the N is in a pyramid of a temporal bone also a facial nerve, peripheral paresis or paralysis often joins the mentioned symptoms facial nerve (see).

P.'s neurinoma - at. the N, or a neurinoma of an acoustical nerve, grows slowly, it gradually squeezes cochlear and facial nerves in internal acoustical pass, leaves it and gradually carries out a mostomozzhechkovy corner, squeezing its educations — a cerebellum, the bridge and cranial nerves. It causes symptoms of a disease: noise in an ear, decrease in hearing, and then and deafness. Over time disturbances of static and dynamic coordination, a spontaneous nystagmus, and in the started cases and other symptoms of defeat of a brain trunk — disturbance of phonation and swallowing develop. Besides, also all-brain symptoms — a headache, congestive changes of an eyeground, etc. accrue. A characteristic symptom of a disease is the expansion of internal acoustical pass revealed by method of a kraniografiya (see. Kraniografiya , Middle ear ). By means of a computer tomography (see. Tomography computer ) diagnose tumors of the small size — with a diameter more than 1,5 — 2 cm. Treatment of neurinoma of P. - at. N only operational.

Operations

for many years widely applied enucleation of a tumor, at a cut left a part of a tumor and its capsule. It was connected with great technical difficulties and danger of a full oncotomy. After enucleation in communication with continuation of growth of a tumor there came the recurrence of a disease. Further the operation of total removal of a neurinoma of an eighth cranial nerve developed by Y was generally recognized. The dandy at the beginning of the 20th.

During total removal of a neurinoma make unilateral trepanation of scales of an occipital bone (occipital scales, T.) on the party of defeat. Crosswisely cut a firm cover of a brain and find a tumor. At big neurinoma resect a part of a cerebellum over a tumor and allocate its capsule. Then enuklei-rut a tumor, allocate and completely delete its capsule. At tumors of the big sizes it is very difficult to keep a facial nerve which is usually stretched and intimately connected with a tumor. If the facial nerve does not manage to be kept, after operation unilateral paralysis of face muscles develops. In such cases make plastics of a facial nerve for correction of cosmetic defect, connecting it to the hypoglossal or departing from it upper root of a cervical loop. Use of the microsurgical equipment (see. Microsurgery ) allowed to improve zvachitelno results of total removal of neurinoma — to lower a postoperative lethality to 3 — 5% and to keep a facial nerve at 60 — 70% of the operated patients.

At the heavy course of not giving in conservative therapy of a disease of Menyer make operation on a back cranial pole; at the same time cut predoor part P. - at. N or destroy the receptor terminations in a labyrinth. Operation of crossing of predoor part P. - at. N widely applied in the 20th. Then this operation was left and at the beginning of the 70th was widely adopted enough again that is connected with development of the microsurgical equipment, increase in efficiency of intervention and reduction of number of postoperative complications.




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D. A. Romanenko; V. V. Bobin (An.), E. I. Zlotnik (neyrokhir.).

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