Acoustic neuroma (cerebellopontine angle tumor)

Acoustic neuroma (cerebellopontine angle tumor)
International Classification (ICD) D43.1
Symptoms hearing loss, Tinnitus, Dizziness and balance disorders, Nystagmus, Pain and loss of sense of touch in the face, occipital headache
Possible causes Mutation in Schwann cells

Basics

Acoustic neuroma is a growth on a cranial nerve responsible for hearing and balance. Although the growth is benign, it nevertheless impairs brain function because it is located in very confined areas of the brain, in the internal auditory canal or at the so-called cerebellopontine angle. Depending on its location, the tumor can grow to a few millimeters or even several centimeters in size.

Unfavourable location in the cerebellopontine angle

The cerebellopontine angle (lat. Angulus pontocerebellaris) is a small niche in the brain located very close to the petrous bone. This is where the bridge, the part of the brain that connects the two halves of the cerebrum (i.e. end brain), and the medulla oblongata meet. In addition, the cerebellum (Latin: cerebellum) is also located nearby.

Both the bridge and the medulla oblongata are absolutely necessary structures for our daily life. Many vital processes are controlled here. Without the cerebellum, we would not be able to perform fluid and fine motor coordinated movements.

Since acoustic neuroma usually grows between the cerebellum and the bridge, it is also called cerebellopontine tumor. In addition to these important brain structures, the cerebellopontine angle contains ten of the twelve so-called cranial nerves, which are responsible for a large part of the functions in the head and neck.

Tumour on the vestibulocochlear nerve

The tumour originates from one of these cranial nerves, the vestibulocochlear nerve. For this reason, acoustic neuroma is also known in specialist circles as vestibular schwannoma.

This nerve is responsible for connecting the cochlea in the ear and the organ of balance with the central nervous system (CNS for short). Without it, the information about the position of the body, which is collected in the organ of balance, could not be transmitted and evaluated.

In most cases, the benign tumor separates itself from the neighboring tissue structures with connective tissue and does not form metastases. Acoustic neuroma occurs primarily between the ages of 30 and 60. It accounts for about eight percent of all brain tumors - but generally has a good prognosis.

Causes

Although this disease is neither hereditary nor contagious, it is currently not possible to clarify exactly why it develops. This benign tumor forms in most cases from the so-called Schwann's cells, which are located around the vestibular nerve. These are necessary to isolate the nerve. This can significantly increase the conduction velocity in the nerve pathways.

Small change in the genetic material - big effect

A mutation, i.e. a change in the genetic material, in the Schwann cells causes them to start growing disproportionately fast. In addition, their lifespan is prolonged because the protective program for the self-destruction of old or damaged cells no longer functions.

In rare cases, acoustic neuroma can also occur in connection with the hereditary disease neurofibromatosis type-2. In this case, a defect in the genome of the human body can cause tumors to spread in it. Despite correlation, acoustic neuroma does not occur in every case. However, in about 5% of such cases, acoustic neuroma occurs on both sides at the same time. Then the diagnosis can be more complex, since predominantly only a unilateral symptom picture for this tumor occurs.

Symptoms

If you have acoustic neuroma, you may not notice it for the first few years because the tumor grows very slowly.

It is not the tumour but the environment that causes symptoms

It is not the tumour itself that is important for symptoms, but the environment surrounding the tumour. Symptoms only arise when the tumour displaces other structures, preventing them from functioning properly. Despite this dependence on the location of the tumour, some typical symptoms can be described which occur in a large proportion of patients.

Reduction of hearing

The tumor develops as described from Schwann's cells located around the vestibulocochlear nerve. When this irritates or depresses the nerve, it leads to increasing hearing loss on the affected side. Usually the first thing noticed is a hearing loss at high frequencies (e.g. birds chirping). Often, the affected person only notices such a hearing loss by chance - e.g. during a telephone conversation. This then becomes more and more pronounced as the tumour grows and can affect not only the organ of hearing but also the organ of balance.

What is most significant is that in most cases the damage is unilateral. It is very unlikely that two acoustic neuromas will form and grow at the same time in the same place, and this is only common in certain hereditary diseases.

Tinnitus

In addition to a reduction in hearing ability, tinnitus can also occur. This is an annoying and unpleasant sound that is constantly heard even though it is not actually there. For most patients, tinnitus is far more disturbing and noticeable than the faint hearing loss that initially occurs. Nevertheless, hearing loss is the most commonly described initial symptom of acoustic neuroma.

Restriction of the organ of balance

As the tumor grows, the limitations become more severe. Dizziness and balance disorders often occur. Both spinning and swaying vertigo can occur, which are very discrete at first, but then increase significantly and thus also greatly affect everyday life.

In addition to the dizziness symptoms, a so-called nystagmus can also occur. This means that one eye starts to tremble again and again when trying to track an object.

Pain and loss of sense of touch in the face

As mentioned earlier, a lot of cranial nerves are located in the area of the cerebellopontine angle. So are the nerves that supply the face. This can result in severe facial pain, movement disorders or even loss of sensation. However, these symptoms are very rarely observed today, since the tumor would have to be relatively large in order to damage the corresponding nerves. Thanks to new examination methods, however, acoustic neuroma is diagnosed and treated much earlier today.

Other neighbourhood symptoms

There can be a whole range of other so-called neighbourhood symptoms. One of the more common symptoms is seeing double images.

In the late stage of the tumour, the cerebellum can also be affected. This leads to gait disorders, as the cerebellum is mainly responsible for the coordination of movement.

Brain pressure in large tumours

If the tumour remains undetected for a long time, so-called intracranial pressure symptoms occur. These occur when the entire brain is under pressure due to the growth of the tumour, as the skull cannot expand. This can be the case even if the tumour is only a few centimetres in diameter.

The symptoms include headaches, which are mainly heard in the area of the back of the head, visual disturbances up to the loss of vision, vomiting and increasing personality changes.

Slow growth

In the majority of cases, the symptoms initially go unnoticed or are only very discreetly noticeable. This is due to the slow growth rate. This is because the brain is very adaptable and tries to compensate for the symptoms by increasing constriction over a long period of time.

Only when the displacement by the tumour is so great that nerve tracts are affected and nerve cells damaged, do the symptoms slowly set in. In many cases, this takes the tumor several years, if not decades.

Rapid symptoms due to haemorrhages

Nevertheless, one should never assume that it cannot be a tumor if symptoms appear suddenly and unexpectedly or worsen drastically. For example, acute bleeding into the tumor can cause massive symptoms within seconds or minutes. These may be accompanied by hearing loss, tinnitus, dizziness and gait disturbances. Sometimes the symptoms are confused with those of a hearing loss, as they are very similar. In a hearing loss, a sudden and almost complete hearing loss forms in the ear affected by the tumor.

Diagnosis

The first step in the diagnosis is always the anamnesis, i.e. the detailed questioning of the patient. This can already provide some clear indications of the tumor, which can then be confirmed with further examinations. The patient usually visits an ENT doctor (i.e. ear, nose and throat doctor) or a neurologist (i.e. neurologist).

Checking the hearing ability

As one of the first examinations, a hearing test is useful, because the acoustic neuroma first shows itself in a reduced hearing ability. Patients listen to different high frequencies or tones (i.e. sound audiometry) or spoken words (i.e. speech audiometry) through headphones. Since the person concerned can indicate what he or she hears, this is a subjective test.

So-called audiometry can be used to determine not only which ear is hearing impaired, but more importantly, the extent of the tumor formation.

Checking the balance

A small temperature test can also be used to find out whether the organ of balance is damaged. The so-called calorimetry is done by alternately rinsing the ear with cold and warm water. Consequently, this changes the membrane potential of the sensory cells and causes the affected eye to twitch. If there are different sensations in the side comparison, this indicates an acoustic neuroma.

First indications of the damage to the balance can also be collected by simple balance tests. This involves performing certain walking and standing tests with the eyes closed. The Romberg and Unterberger tests in particular provide good indications of damage to the balance organ. A nystagmus (i.e. eye twitching) to the healthy side is a further indication of a restriction of the sense of balance.

Brainstem audiometry

Brainstem evoked response audiometry (BERA) can also be performed. The auditory nerve is tested with the aid of a loudspeaker. Various clicking sounds are played to the patient, which are measured without his active participation via an electrode behind the ear. The information from the sound is transmitted directly to the brain via the auditory nerve and measured by the measurement sensors.

This would be conspicuous if the vestibulocochlear nerve were damaged by the tumour. The test takes between twenty and sixty minutes.

Radiological examinations

The final diagnosis is then usually made by means of a radiological examination. Computer tomography (CT) and magnetic resonance imaging (MRI) play an important role in this. MRI is particularly important for early diagnosis. MRI does not cause any radiation exposure. With this procedure, special contrast agents can detect neurinomas that are only a few millimetres in size.

Therapy

In the treatment of acoustic neuroma, three different strategies can be pursued depending on the situation. On the one hand, one can wait, on the other hand, one can surgically remove the neurinoma or have it irradiated.

Wait and see

Especially small acoustic neuromas with a diameter of a few millimeters can be observed in a controlled manner for the time being. At least as long as no typical symptoms appear, it may be most efficient under certain circumstances to check the further development with regular controls. For this purpose, physicians use MRI procedures at regular intervals to analyze tumor growth.

Since acoustic neuromas develop very slowly over a period of years, major surgery or radiation treatment can be avoided, at least for the time being, in the absence of symptoms. In older patients, the tumor size usually changes little - in some cases it even decreases.

Surgical removal

When a size of about three centimetres has been exceeded or symptoms appear, the tumour must be surgically removed. This is done with extreme caution, on the one hand to get the entire tumor and on the other hand not to damage surrounding structures (healthy tissue, blood vessels and nerves).

Depending on the size of the tumour, however, the risk of impairing hearing or the sense of balance is very high. If the operation is unsuccessful, bleeding or nerve damage can occur, which can even cause long-term impairment of the sense of hearing and balance.

Radiation therapy

As an alternative to surgery, radiation therapy can be administered using a radiation therapy device such as a gamma or cyber knife. The major advantage is that there are fewer complications than with real surgery. In this procedure, the cells of the tumor are destroyed by radiation. In most cases, larger tumours are not completely removed - consequently, a controlled wait is carried out to see whether the body itself breaks down the cell remnants. However, it is not absolutely possible to avoid damaging healthy tissue, which is why this form of therapy is only used for patients who cannot undergo surgery for medical reasons.

Forecast

Acoustic neuromas are characterized by the fact that they grow very slowly and do not form metastases. Especially in patients who are already over 60 years old, the tumor growth is very small. The course of the disease is determined by the brain region in which the neurinoma grows and its size. Symptom-free, small tumours can be observed with regular medical check-ups without therapy.

Good prognosis with early diagnosis

As with all other tumors, the prognosis is much better if the diagnosis was made early. In this case, larger tumors can be removed with the help of surgical procedures, and they usually do not recur.

Regular control after removal

In rare cases, a recurrence of the tumour can occur after removal. For this reason, it is advisable to have regular check-ups with an MRT. In this way, even very small recurrences can be detected, which can then be removed quickly and easily.

Especially small and medium-sized tumours can usually be removed completely without causing any major damage.

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