Auditory neurinoma

The diagnosis of acoustic neuroma (otherwise known as vestibular schwannoma) means that a tumor has developed in the myelin sheath of the vestibulocochlear nerve (8th cranial nerve).

This primary intracranial neoplasm, formed by glial (Schwann) cells, is benign. However, it can grow, which leads not only to hearing loss, but also to other negative consequences.

According to medical statistics, acoustic neuromas account for 5 to 10% of all cases of craniocerebral neoplasms.

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Causes of acoustic neuroma

Acoustic neuroma can be unilateral or bilateral, with almost 96% of cases being unilateral. To date, the causes of acoustic neuroma that occurs only on one side have not been fully clarified. Although there is a version that this sporadic form of the disease is a consequence of increased radiation, which leads to the destruction of the myelin sheath of nerve fibers.

But the etiology of bilateral neurinoma is directly related to such a rare hereditary pathology as neurofibromatosis type II. With this disease, genetically determined mutations occur in the cells of various parts of the nervous system, which lead to the growth of benign tumors (neurofibromas, meningiomas, gliomas, schwannomas). And bilateral acoustic neurinoma, which can form even in adolescents, is considered the main sign of neurofibromatosis type II. According to experts, patients with this diagnosis have an almost 100% chance of developing bilateral acoustic neurinoma, and, as a rule, by the age of 30 they lose the ability to hear.

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Symptoms of acoustic neuroma

This benign tumor appears in the multilayered myelin sheath of the cranial nerve - nervus acusticus (VIII pair), which is located in the internal auditory canal and unites two separate nerves - the auditory (nervus Cochlearis) and vestibular (nervus Vestibularis). The neoplasm can capture one of them or both at once, but it usually does not grow into the structure of other tissues, but only presses on closely adjacent surrounding nerve fibers, cerebellar vessels and brainstem structures.

Acoustic neuromas develop quite slowly, so the onset of the pathological process is asymptomatic. And all the symptoms of an acoustic neuroma appear as its size increases and are related to the areas on which the tumor begins to exert pressure and how intense it is.

As clinical practice shows, the very first sign of this disease is ringing and noise in the ear (tinnitus) and a feeling of congestion. Over time, a person begins to hear worse with this ear, but hearing decreases gradually. The consequences of an acoustic neuroma, when its diameter reaches 2.5-3 cm and continues to increase, are complete hearing loss.

Depending on the size of the tumor and its location in the ear canal, the following symptoms of acoustic neuroma are observed:

• dizziness and impaired coordination of movements (loss of balance when turning the head sharply and changing body position) - caused by pressure from the tumor on the vestibular part of the affected nerve;
• Nystagmus (involuntary rhythmic movements of the eyeballs) is the result of pressure from the neuroma on the brainstem;
• loss of sensitivity and numbness (paresthesia) of half of the face on the side of the affected nerve - caused by pressure from the tumor on the facial nerve, which innervates all facial muscles;
• pain in the facial area (trigeminal prosopalgia) on the side of the neuroma is the result of pressure from the tumor on the trigeminal nerve;
• loss of taste in the front of the tongue and disturbances in salivation – caused by compression of the 12th cranial nerve;
• swallowing and articulation disorders - due to compression of the glossopharyngeal and vagus nerves;
• decreased sensitivity of the cornea of the pupil (change in the corneal reflex);
• double vision (diplopia) is a consequence of damage to the oculomotor nerve;
• headache, nausea and vomiting are the result of increased intracranial pressure.

Increased intracranial pressure occurs with large sizes of the acoustic neuroma, which begins to press on the internal cerebrospinal fluid spaces of the brain. As a result, the work of the ventricular system of the brain is disrupted, excess cerebrospinal fluid accumulates in the ventricles of the brain and hydrocephalus occurs. And this is a real threat of damage to the vital centers of the brain stem.

Diagnosis of acoustic neuroma

The main methods of otoneurological examination for the purpose of diagnosing acoustic neuroma are X-ray of the temporal bones in transverse projection (according to Stenvers), computed tomography (CT), magnetic resonance imaging (MRI), audiography (detection of hearing impairment) and electronystagmography.

It should be noted that if the size of the neuroma is up to 1.5 cm, computed tomography may not reveal the presence of a tumor, and an incorrect diagnosis is possible - sensorineural hearing loss, which has a similar clinical picture in the initial stages.

The most informative diagnostic method and standard for diagnosing acoustic neuroma is magnetic resonance imaging of the brain in various projections.

MRI for acoustic neuroma is performed on absolutely all patients with this diagnosis or its assumption. The study is performed using a contrast agent administered intravenously. Such a tomogram allows you to clearly determine the size of the neoplasia (it has an oval shape with clear, even contours), to identify the tumor matrix (the place where it begins to grow), which in the vast majority of cases is located in the internal auditory canal (adjacent to the posterior surface of the pyramid of the temporal bone) or in the pontine cerebellar angle, which ends this canal.

Axial and frontal MRI projections for acoustic neuroma make it possible to see signs of widening of the auditory canal, how deeply the tumor has grown into the cranial cavity, and what neurovascular structures it has affected.

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Treatment of acoustic neuroma

Treatment of acoustic neuroma is performed by surgical removal, radiation therapy, and radiosurgery. But in some cases, for example, with long-term hearing loss or mild symptoms (especially in the elderly), only dynamic monitoring of the disease with periodic control examinations is used.

Removal of acoustic neuroma by open surgery is necessary if the tumor grows and the disease progresses in young and middle-aged patients, or when relapses occur after the first operation to remove it. Radiation or radiosurgery is used when the neuroma is small and the symptoms of the disease are mild.

Radiation therapy and radiosurgery

Treatment of acoustic neuroma with its irradiation does not remove the neoplasm and is used to slow down or stop its further growth. Radiation therapy - fractionated stereotactic radiotherapy - is carried out repeatedly in small doses. However, as doctors note, fractionated irradiation is used in the treatment of acoustic neuroma as a last resort - due to the risk of tumors appearing in the trained brain tissues.

Radiosurgery is a more modern method of radiation therapy using a high dose of ionizing radiation. The flow of gamma rays with the help of Gamma Knife and Cyber Knife devices is focused precisely on the tumor - thanks to the stereoscopic X-ray navigation system. In addition to positive results, radiosurgery for acoustic neuromas has other advantages.

Firstly, healthy brain tissues are irradiated in minimal doses. Secondly, this treatment is painless. Thirdly, radiosurgery is a non-traumatic method, so the rehabilitation period for patients after such treatment is significantly shorter than after conventional surgery.

Surgery for acoustic neuroma

The decision on direct surgical intervention is made based on a comprehensive analysis of the clinical picture of the disease in a particular patient - taking into account his age, general condition, size of the tumor and the hearing loss rate. The main goal pursued by the operation for acoustic neuroma is to remove the tumor and stop the pathological process. But it is impossible to restore lost hearing with a scalpel.

To reach the neurinoma, the surgeon needs to enter the internal auditory canal, a bony canal 10-12 mm long and about 5 mm in diameter. The canal begins with an opening on the back surface of the pyramid of the temporal bone of the skull, crosses it and reaches the pontine-cerebellar angle, which is located between the brainstem and the cerebellum.

In neurosurgery, three methods (surgical approaches) have been developed for removing acoustic neuroma: translabyrinthine, suboccipital and through the middle cranial fossa.

With the translabyrinthine approach (through the outer wall of the labyrinthine part of the middle ear), the skull is opened (craniotomy) behind the ear, a small segment of the middle ear is removed, and then the tumor itself. With this approach, the nerve can be seen and the entire neuroma can be removed, but after the operation, the patient irreversibly loses the ability to hear with that ear. In addition, in a large number of cases, there is a persistent dysfunction of the vestibular nerve, which forms a pair with the auditory nerve.

Suboccipital (suboccipital) access is performed by opening the skull in the area under the back of the head and is used to remove tumors of significant size. After such an operation, the chances of preserving the remaining hearing are much higher. According to statistics, when removing an acoustic neuroma of 3 cm or more, hearing can be preserved in almost a quarter of the patients operated on.

If it is decided to remove the acoustic neuroma through the middle cranial fossa (which is located between the large wings of the sphenoid bone, the sella turcica and the anterior surface of the pyramid of the temporal bone), then the size of the neuroma does not exceed 1.5-2 cm in diameter, and hearing preservation is possible. According to some data, hearing is preserved in the range of 15-45% of such operations.

Postoperative period for acoustic neuroma

Surgery for this pathology is performed under general anesthesia, with craniotomy (cranial trepanation). The postoperative period for acoustic neuroma is quite long. In addition, the possibility of damage to other nerves located in the area of intervention in the brain structures during the operation is not excluded. It is because of these injuries that various complications may arise in patients who have undergone surgery.

Thus, when the vestibular nerve is damaged, there is a loss of balance, which may go away over time. But the lack of coordination of various muscles (ataxia) threatens to be lifelong. And in general, as neurosurgeons say, after such an operation the vestibular nerve very rarely functions normally.

If the facial nerve is affected, problems with closing the eye (lagophthalmos) and peripheral paralysis of the facial muscles (prosoplegia) are possible. Disturbance of the trigeminal nerve (V pair) is expressed in disturbances of sensitivity in the face. Problems with swallowing after surgery indicate damage to such cranial nerves as the glossopharyngeal, vagus and hypoglossal.

And when the neoplasm has been removed from the brainstem, then in the postoperative period for acoustic neuroma (as well as the rest of the time), patients may feel numbness in parts of the body on the side opposite the affected nerve - contralateral paresthesia.

Prevention of acoustic neuroma

Today, it is practically impossible to prevent the occurrence of any neoplasm - especially of unknown etiology. Therefore, prevention of acoustic neuroma consists only in the fact that in case of persistent noise in the ear and hearing loss, a person needs to consult an otolaryngologist. Because if these are the first symptoms of acoustic neuroma, then timely adequate medical measures will help get rid of the tumor and avoid damage to other cranial nerves.

Prognosis of acoustic neuroma

It is possible to give a prognosis for acoustic neuroma. First of all, it depends on its "dimensions". With the help of radiosurgery, a small tumor stops growing in almost 95 cases out of 100. However, after conventional surgical removal, almost every fifth tumor continues to grow...

It is especially worth emphasizing that the acoustic neuroma is extremely rarely malignant, that is, degenerates into cancer. In addition, spontaneous reduction of the neuroma is observed in almost 6% of cases.