Acoustic neuroma

definition

The most frequent tumor of Inner ear is the acoustic neuroma. Other names for it are Cerebellar bridge angle tumor and Vestibular schwannoma.

This is a neuroma or schwannoma in the inner part of the Ear canal or a neuroma in the cerebellopontine angle. A neuroma or schwannoma is one benign and mostly slowly growing tumor. It starts from the Schwann cells. These are the cells that envelop the peripheral annoy form, so the Nerve fibers not im Spinal cord and brain lie.
This covering of the nerve fiber is relevant for supporting the nerve cell and also for its myelination. The myelination allows the nerve fiber to conduct electrical signals faster, with less loss and thus over longer distances. But it is precisely from these cells that a tumor can originate in the event of excessive proliferation (growth).

Depending on where such a tumor arises, it is given different names and causes different symptoms. However, one thing that most acoustic neuromas have in common is that, as their name suggests, their starting point is the auditory nerve (Vestibular nerve) is.

Function of the auditory nerve

Of the Vestibular nerve lies along with the for a large part of its course Cochlear nerve. Together they make that Vestibulocochlear nerve, the eighth cranial nerve.

The vestibular nerve is the nerve that makes this Balance organ innervated. This means that it transports information from the organ of equilibrium to other structures in the brain in order to enable a link between all stimuli that humans perceive.
The Balance organ located in the inner ear. It refers to three semicircular canals and two macular organs through which the organism can perceive and classify movements.
Since there are three semicircular canals that are almost perpendicular stand to each other, all three levels of space and movements in them can be perceived, e.g. the Turning the head.
The macular organs pass on information about linear accelerations, such as the Gravity, at the Brakes and Acceleration in vehicles and also with one Fall.

Usually, the electrical signals that enter the brain via the left and right vestibular nerves become a Picture of the location, position and movement of the body formed in space.
In the event of failures and injuries, incorrect or no information from the respective Balance organ more to the brain and lead to wrong conclusions being made by the processing centers in the brain.

The other part of the eighth cranial nerve is that Cochlear nerve. This innervates the cochlea. This is a bony shell-like structure, which is responsible for the hearing ability.
If this nerve is injured, information may no longer be sent to the brain.

Classification

The classification of Acoustic neuromas is possible according to two systems.

To Wigand become three stages from A to C named:

• Stage A: in the internal ear canal, smaller than 8mm in diameter
• Stage B: grows into the cerebellopontine angle, diameter between 9-25 mm
• Stage C: grows to the brain stem, larger than 25mm

To Samii become six types assigned:

• T1: only in the internal ear canal
• T2: grows inside and outside the ear canal
• T3a: grows in the space between the cerebellum and the brain stem
• T3b: is in contact with the brain stem
• T4: the brain stem is compressed
• T4b: in addition, the parts of the liquor spaces are relocated (4th ventricle)

Symptoms

Depending on where the acoustic neuroma occurs, other symptoms develop.

If the tumor is intrameatal, i.e. in the internal auditory canal, the vestibulocochlear nerve is primarily affected.
The early symptom is unilateral hearing loss, which often becomes noticeable slowly and insidiously. Patients often only notice this hearing loss during routine medical examinations. Often it is also noticeable when telephoning - the earpiece must be held closer to the ear on the affected side or the person you are speaking to is only heard very poorly. Furthermore, higher tones are perceived worse.
With an acoustic neuroma, sudden hearing loss can also occur. This is not a creeping hearing loss, but a sudden one-sided hearing loss. This usually heals spontaneously. However, if further hearing loss occurs repeatedly, this can be a sign of an acoustic neuroma, which disrupts the blood flow to the inner ear.
Another and sometimes the only symptom is ringing in the ears or ringing in the ears (tinnitus). However, hearing loss does not have to be associated with this from the start, although this can certainly occur in the further course.
Dizziness and balance disorders occur when the vestibular nerve is pressed, although these usually do not occur at rest, but initially only during exercise.
The dizziness shows up e.g. when walking in the dark or by swaying. Sudden attacks of dizziness or persistent dizziness when resting are less common.

In later phases, when the tumor is spreading or extrameatal (outside of the ear canal), e.g. In the cerebellopontine angle (KBW), further symptom complexes appear.
Due to the often very slow growth of the acoustic neuroma, the brain can adjust to the situation and reduce the symptoms of the failure over a longer period of time.
The cerebellar bridge angle is the name for a narrow space between the cerebellum (cerebellum) and the brain stem (truncus cerebri).
In addition to the vestibulocochlear nerve, other nerves such as the facial nerve and the trigeminal nerve run along here.

In the case of disorders of the facial nerve (7th cranial nerve), there are failures in the facial area. The facial muscles are innervated by the facial nerve, so that an acoustic neuroma can also paralyze these muscles. Often a weakness of the eye-closing muscles (eyelid closure weakness of the orbicularis oculi muscle) first becomes apparent.
Furthermore, the innervation of the lacrimal glands and the oral salivary glands takes place via the facial nerve, so that the production of tear fluid and saliva can also be impaired.
In addition, part of the facial nerve, the chorda tympani, directs taste perception from the front two thirds of the tongue, so that in rare cases patients can also complain of problems with taste.
Sensitive perception in the external auditory canal occurs through one of the branches of the facial nerve, the posterior auricular nerve, and the auricularis nervi vagi branch, a branch of the vagus nerve (10th cranial nerve). In the case of an acoustic neuroma, these nerve branches can be pinched off and lead to a loss of sensitivity in the external auditory canal. The clinical name for this is Hitselberger's sign.

The third nerve is the trigeminal nerve in the cerebellopontine angle. He is responsible for the sensitive care of the facial skin. If it is pinched off, the sensation in the face may fail. In addition, the corneal reflex runs over it, which can be reduced or absent in acoustic neuromas. This reflex describes the process that when the cornea is touched, a reflex-like closure of the eye takes place. A touch is perceived through the trigeminal nerve.

Other later symptoms affect other cranial nerves in the region, such as the vagus and glossopharyngeal nerves (9th cranial nerve). If they are affected, swallowing disorders and further loss of taste can be part of the symptoms.

If the acoustic neuroma is not discovered or it grows rapidly, it can take on sizes that have life-threatening consequences.
The position in the cerebellopontine angle makes an acoustic neuroma dangerous in the sense that the brain stem is in close proximity.
The brainstem contains vital centers for breathing, alertness and alertness of the organism (ARAS, ascending reticular activating system), circulatory modulation (increasing and decreasing blood pressure) and motor activity (parts of the extrapyramidal system, which is important for the modulation and control of signals for different muscle groups).
If the acoustic neuroma becomes so large that these centers are pinched off, then that is not compatible with life.

In addition, an acoustic neuroma harbors the risk of obstructing the drainage pathways for cerebral fluid (liquor). The liquor is a liquid that is located in the brain in specially designated spaces, the liquor spaces. There is a very precise process of new production and drainage of this liquid. Should this drain, e.g. in the case of an acoustic neuroma, the fluid builds up and the pressure in the brain increases.
Hydrocephalus (head of water) develops. This manifests itself in (gushing) vomiting, headache and a congestive papilla (the increased fluid causes swelling in the inner eye). Furthermore, disturbances of consciousness and coma can occur.

diagnosis

At the beginning of the diagnosis, as in other places, there is also the anamnesetalking to the patient. Based on the symptoms described, a specialist can make the suspected diagnosis of an acoustic neuroma relatively quickly.

This suspicion can be investigated using various tests.

For one, can about Hearing tests determine whether there is a subjective hearing loss. The tones become more different frequency and volume played. On the basis of the thresholds for perceiving the tones, the attending physician can create an overview of the hearing perception and estimate to what extent it is a normal or pathological condition.

In the next step, the Stimulus conduction of the auditory nerves be checked. Various tones are played to the patient under computer control. over Electrodes on the head it can be measured to what extent signals are transmitted via the cochlear nerve and whether these are in the brain arrived. By measuring the transmitted signals, it can be recognized whether there is damage or conduction problems in the auditory nerve. The advantage of this method is that it is possible to work independently of the patient's subjective perception. This method is called BERA (brain stem electic response audiometry). Extended lead times indicate damage.

On the other hand, the function of the Balance organ be checked. The extent to which a Nystagmus triggerable. A nystagmus is a jerky movement in the eye that is controlled by reactions in the organ of equilibrium. You can easily perceive this process yourself in a moving train. The eye fixes an object and quickly moves in the direction of travel when the object disappears and fixes a new object.
This nystagmus can artificially triggered when the ear is rinsed with warm liquid. Then a separate part of the Balance organ, one of the semicircular canals, irritates and draws a reflex eye movement with it.
Should the reaction on the eye fail or on both sides turn out differently, that is a good sign that there is damage to the Balance organ exist. The movements on the eye are made possible by the use of a Frenzel glasses made visible on the patient. These are glasses that the patient puts on, with very highly refractive lenses that prevent the patient from fixing objects in the vicinity, which would falsify the result.
A similar possibility that Balance organ stimulating is to sit the patient on a swivel chair and observe the eye movements, as well as after abruptly stopping the turning movement. Here, too, Frenzel glasses are used to better represent the movements.
Both methods are wise Failures and inexcitability nystagmus or the occurrence of spontaneous nystagmus (without stimulus) for possible damage.
Furthermore, this can Balance organ over different Walking and standing attempts getting tested.

The actual representation of the acoustic neuroma, however, enables this MRI of the head (Nuclear spin) with Contrast media. The entire region in the area of ​​the inner ear and cerebellopontine angle can be displayed very precisely via very thin sections. Even very small tumors in the range of a few millimeters are noticeable here. Changes in the tissue can be made clearly visible through the contrast agent, since e.g. Tumors have a different uptake of contrast agent.
Furthermore, a CT (Computed tomography) made of the skull. Here they do not show the soft tissues as well as in the MRI of the head, but the bony area can be shown well.

therapy

The surgery an acoustic neuroma is a possible therapy.

Tumors that are in the inner ear canal lying to be removed. If the hearing function is still available, an attempt is made to maintain it. In this case, the skull is pulled over from the side Temporal bone (Temporal bone) open - the transtemporal approach.
This path harbors risk potential because parts of the Facial nerve (Facial nerve) exposed and possibly damaged.

If the patient has already lost hearing on the affected side, surgery is performed directly on the ear. In this case a translabyrinthine surgery instead of completely removing the inner ear during the operation. This access route reduces the risk of damaging other nerves.

For very large tumors that have grown into the cerebellopontine angle, the operation is suboccipitally. The bone behind the ear is separated and an access is created into the cranial cavity through which the surgeon can remove the tumor. In this way, it is possible to maintain the hearing function.