Neurinoma of the anterior cochlear nerve.

The vestibulocochlear nerve neurinoma is a disease that has been the subject of a large number of studies. In recent years, due to the development of radiation and other technologies for visualizing tumor formations of the pyramid of the temporal bone and the cerebellopontine angle, as well as video and microsurgical methods, the problem of vestibulocochlear nerve neurinoma has become solvable from being extremely difficult at the beginning of the 20th century.

By the middle of the last century, vestibulocochlear nerve neurinoma accounted for 9% of brain tumors and 23% of posterior cranial fossa tumors, while posterior cranial fossa tumors accounted for 35% of all brain tumors, while vestibulocochlear nerve neurinoma accounted for 94.6% of lateral cistern tumors. The disease is most often diagnosed at the age of 25-50 years, but can also occur in children and the elderly. In women, vestibulocochlear nerve neurinoma occurs twice as often.

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Pathogenesis of vestibulocochlear nerve neurinoma

The vestibulocochlear neurinoma is a benign encapsulated tumor that primarily develops in the internal auditory canal from the vestibular nerve neurolemma with further growth towards the cerebellopontine angle. As the tumor grows, it fills the entire space of the lateral cistern of the brain, significantly stretching and thinning the cerebral-pontine angle CNs (vestibule-cochlear, facial, intermediate and trigeminal) located on its surface, which leads to trophic disorders and morphological changes in these nerves that disrupt their conductivity and distort the functions of the organs they innervate. Filling the entire internal auditory canal, the tumor compresses the internal auditory artery that supplies the structures of the inner ear, and when it reaches the cerebellopontine angle, it puts pressure on the arteries that supply the cerebellum and brainstem. By exerting pressure on the bone walls of the internal auditory canal, the tumor causes their resorption, which leads to a radiographic sign of its expansion, and upon reaching the apex of the pyramid - its destruction, after which the tumor rushes to the pontocerebellar angle, experiencing neither mechanical obstacles nor a lack of nutrients in its free space. It is here that its rapid growth begins.

Large tumors displace and compress the medulla oblongata, pons, cerebellum, causing corresponding neurological disorders due to damage to the nuclei of the cranial nerves, vital centers and their conducting pathways. Small tumors (2-3 mm) with a long development cycle can be asymptomatic and detected accidentally during biopsy. Such cases, according to B.G. Egorov et al. (1960), accounted for up to 1.5% in the last century. In 3% of cases, bilateral tumors are observed; they usually occur with widespread neurofibromatosis (Recklinghausen's disease). Gardner-Turner syndrome, which occurs with hereditary bilateral neurinoma of the vestibulocochlear nerve, should be distinguished from this disease.

Symptoms of vestibulocochlear neuroma

The classical division of the clinical forms of vestibulocochlear neurinoma into four periods does not always correspond to the chronological sequence of the signs characteristic of these periods. And although in most cases the clinical manifestations of vestibulocochlear neurinoma are directly dependent on the growth rate of the tumor and its size, there may also be atypical cases when ear symptoms (noise, hearing loss, dizziness) can be observed with small tumors, and, conversely, when neurological signs that occur when the tumor enters the pontocerebellar angle appear, bypassing the otiatric symptoms of vestibulocochlear neurinoma.

There are four clinical periods of development of vestibulocochlear nerve neurinoma.

Otiatric period

In this period, the tumor is located in the internal auditory canal and the symptoms of vestibulocochlear neurinoma caused by it are determined by the degree of compression of the nerve trunks and vessels. Usually, the first signs to appear are those of impaired auditory and gustatory functions (tinnitus, perceptual hearing loss without FUNG). At this stage, vestibular symptoms are less constant, but it is possible that they go unnoticed because they are quickly leveled by the central compensation mechanism. However, with a bithermal caloric test using videonystagmography at this stage, it is often possible to establish a sign of asymmetry along the labyrinth within 15% or more, indicating suppression of the vestibular apparatus on the affected side. At this stage, in the presence of dizziness, spontaneous nystagmus can be registered, directed first towards the "sick" ear (irritation due to hypoxia of the labyrinth), then towards the "healthy" ear due to compression of the vestibular portion of the vestibulocochlear nerve. At this stage, the OKN is usually not disturbed.

Sometimes in the otitis period, Meniere-like attacks may be observed, which can imitate Meniere's disease or vertebrogenic labyrinthopathy.

Otoneurological period

A characteristic feature of this period, along with a sharp increase in otiatric symptoms caused by damage to the vestibulocochlear nerve, is the emergence of signs of compression of other cranial nerves located in the cerebellopontine angle due to the tumor entering its space. Usually, this stage occurs 1-2 years after the otiatric stage; it is characterized by radiographic changes in the internal auditory canal and the apex of the pyramid. Also characteristic are severe hearing loss or deafness in one ear, loud noise in the ear and the corresponding half of the head, ataxia, impaired coordination of movements, and deviation of the body toward the affected ear in the Romberg position. Attacks of dizziness become more frequent and intensify, accompanied by spontaneous nystagmus. With significant tumor sizes, gravitational positional nystagmus appears when the head is tilted to the healthy side, caused by the displacement of the tumor toward the brainstem.

During this period, dysfunctions of other cranial nerves arise and progress. Thus, the effect of the tumor on the trigeminal nerve causes paresthesia on the corresponding half of the face (Barré's symptom), trismus or paresis of the masticatory muscles on the side of the tumor (Christiansen's symptom). At the same time, a symptom of a decrease or disappearance of the corneal reflex on the same side is observed. At this stage, dysfunction of the facial nerve manifests itself only as paresis, most pronounced for its lower branch.

Neurological period

During this period, otiatric disorders recede into the background, and the dominant position is occupied by neurological symptoms of vestibulocochlear nerve neurinoma, caused by damage to the nerves of the pontine-cerebellar angle and pressure of the tumor on the brainstem, pons and cerebellum. These signs include paralysis of the oculomotor nerves, trigeminal pain, loss of all types of sensitivity and corneal reflex on the corresponding half of the face, decreased or loss of taste sensitivity on the posterior third of the tongue (damage to the glossopharyngeal nerve), paresis of the recurrent nerve (vocal fold) on the side of the tumor (damage to the vagus nerve), paresis of the sternocleidomastoid and trapezius muscles (damage to the accessory nerve) - all on the side of the tumor. At this stage, vestibular-cerebellar syndrome is clearly expressed, manifested by gross ataxia, multidirectional large-scale, often undulating nystagmus, ending in gaze paresis, pronounced vegetative disorders. In the fundus - congestion on both sides, signs of increased intracranial pressure.

Terminal period

As the tumor grows further, cysts filled with yellowish fluid form in it; the tumor increases in size and presses on vital centers - respiratory and vasomotor, compresses the cerebrospinal fluid pathways, which increases intracranial pressure and causes cerebral edema. Death occurs from blockade of vital centers of the brain stem - respiratory and cardiac arrest.

In modern conditions, the third and fourth stages of vestibulocochlear nerve neurinoma are practically not encountered; existing diagnostic methods, with the appropriate oncological alertness of the doctor to whom the patient turns with complaints of the appearance of constant noise in one ear, hearing loss in it, dizziness, provide for the implementation of appropriate diagnostic techniques to determine the origin of the said complaints.

Diagnosis of vestibulocochlear nerve neurinoma

The diagnosis of vestibulocochlear neurinoma is difficult only in the otitis stage, when in most cases there are no radiographic changes in the internal auditory canal, while such a patient may have radiographic changes in the cervical spine, especially since, according to A.D. Abdelhalim (2004, 2005), every second person, starting from the age of 22, develops initial radiographic signs of cervical osteochondrosis and complaints, often similar to the subjective sensations that occur with vestibulocochlear neurinoma. Starting from the oto-neurological (second) stage, the tumor of the internal auditory canal is practically detected in all cases, especially when using such highly informative methods as CT and MRI.

Such radiological projections as the Stenvers projection, the Highway III projection, and the transorbital projection with visualization of the pyramids of the temporal bone also have a fairly high information content.

Differential diagnostics of vestibulocochlear nerve neurinoma is difficult in the absence of radiographic changes in the internal auditory canal. Differential diagnostics are performed with cochleovestibular disorders in vertebrobasilar vascular insufficiency, auditory nerve neuritis, latent forms of Meniere's disease, Lermoyer syndrome, Barany's positional paroxysmal vertigo syndrome, meningioma, and cystic arachnoiditis of the cerebellopontine angle. In addition to the use of modern radiation technologies, qualified differential diagnostics require the participation of an otoneurologist, neurologist, and ophthalmologist.

A certain value in the diagnosis of vestibulocochlear nerve neurinoma is the study of the cerebrospinal fluid. In the case of vestibulocochlear nerve neurinoma, the number of cells in it remains at the normal level and does not exceed 15x10 ⁶ /l, at the same time, a significant increase in the content of protein in the cerebrospinal fluid (from 0.5 to 2 g/l and more) is observed, secreted from the surface of large neurinomas that have prolapsed into the cerebellopontine angle.

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Treatment of vestibulocochlear nerve neurinoma

The vestibulocochlear nerve neuroma is treated exclusively by surgery.

Depending on the size and direction of tumor spread and its clinical stage, surgical approaches such as suboccipital retrosigmoid and translabyrinthine are used.