The classification of acoustic neuroma is possible according to two systems. Three stages from A to C are named after Wigand: Six types are classified according to Samii:
- Stage A: in the inner ear canal, smaller than 8mm in diameter
- Stage B: grows up to the cerebellar bridge angle, diameter between 9- 25mm
- Stage C: grows to the brain stem, larger than 25mm
- T1: only in the inner ear canal
- T2: grows inside and outside the auditory canal
- T3a: grows into the space between the cerebellum and the brain stem
- T3b: is in contact with the brain stem
- T4: the brainstem is compressed
- T4b: additionally, parts of the cerebrospinal fluid spaces are relocated (4th ventricle)
Early symptom is unilateral hearing loss, which is often felt slowly and insidiously. Patients often notice this hearing loss only during routine examinations by their doctor. Often it also becomes noticeable on the phone – the earpiece on the affected side must be held even closer to the ear or the person you are talking to can only be heard very poorly.
This usually heals spontaneously. If, however, further sudden deafness occurs repeatedly, this can be a sign of an acoustic neuroma, which disturbs the blood circulation in the inner ear. Another and sometimes the only symptom is tinnitus (ringing in the ears).
However, this does not necessarily mean that hearing loss is present from the beginning, although it can certainly occur later. Dizziness and disturbances of balance occur due to impressions of the vestibular nerve, whereby these usually do not occur at rest, but initially only when under stress. Dizziness is manifested, for example, when running in darkness or by swaying.
More rare are sudden attacks of dizziness or permanent vertigo at rest. In later phases, when the tumour spreads or lies extrameatally (outside the auditory canal), e.g. in the cerebellar bridge angle (CBC), further symptom complexes become apparent. Due to the often very slow growth of the acoustic neuroma, the brain can adapt to the situation and reduce the symptoms of the failure over a longer period of time.
The cerebellum bridge angle is the name given to 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 also run along this space. In case of disorders of the facial nerve (7th cranial nerve), there are failures in the facial region.
The facial musculature is innervated by the nervus facalis, so that an acoustic neuroma can also lead to paralysis of these muscles. Often a weakness of the eye-closing muscles (weakness of the orbicularis oculi muscle) is initially apparent. Furthermore, the facial nerve also innervates the lacrimal glands and the oral salivary glands, so that the production of tear fluid and saliva can also be impaired.
In addition, a part of the facial nerve, the chorda tympani, conducts taste perception from the front two-thirds of the tongue, so that in rare cases patients may also complain about problems with taste. Sensory perception in the external auditory canal is conducted by one of the branches of the facial nerve, the posterior auricular nerve, and the ramus auricularis nervi vagi, a branch of the vagus nerve (10th cranial nerve). In the case of an acoustic neuroma, these nerve branches can be squeezed and lead to a loss of sensitivity in the external auditory canal.
If it should be disconnected, it can lead to loss of sensation in the face. In addition, the corneal reflex runs over it, which can be reduced or absent in acoustic neuroma. This reflex describes the process that when the cornea touches the eye (cornea), a reflex-like closure of the eye takes place.
The perception of a touch takes place via the trigeminal nerve. Other later symptoms affect other cranial nerves located in the region, such as the vagus and glossopharyngeal nerve (9th cranial nerve). If they are affected, swallowing disorders and further loss of taste may be part of the symptoms.
If the acoustic neuroma is not detected or grows rapidly, it can grow to a size that can be life-threatening. The location in the cerebellar bridge angle makes an acoustic neuroma more dangerous in the sense that the brain stem is in close proximity. The brain stem contains vital centers for breathing, attention and alertness of the organism (ARAS, ascending reticular activating system), circulatory modulation (raising and lowering blood pressure) and motor activity (parts of the extrapyramidal system, which is important for modulating and controlling signals for various muscle groups).
If the acoustic neuroma becomes so large that these centres are squeezed out, then this is not compatible with life. In addition, an acoustic neuroma carries the danger of blocking the drainage of cerebrospinal fluid (liquor). The cerebrospinal fluid is a fluid that is located in the brain in specially designed spaces, the cerebrospinal fluid spaces.
There is a very precise process of new production and drainage of this fluid. If this outflow is prevented, e.g. in the case of an acoustic neuroma, the fluid accumulates and causes an increase in pressure in the brain. A hydrocephalus (hydrocephalus) develops.
This manifests itself in (gushing) vomiting, headache and a congestion papilla (the increased fluid causes swelling in the inner eye). Furthermore, it can lead to disturbances of consciousness and coma. At the beginning of the diagnosis, as in other places, there is the anamnesis, the conversation with the patient.
On the basis of the symptoms described, a specialist can make a suspected diagnosis of an acoustic neuroma relatively quickly. This suspicion can be investigated by means of various tests. On the one hand, hearing tests can be used to determine whether a subjective hearing loss is present.
Sounds of different frequency and volume are played. Based on the thresholds for the perception of the sounds, the attending physician can draw up an overview of the hearing perception and estimate to what extent the condition is normal or pathological. In the next step, the stimulation conduction of the auditory nerves can be checked.
During this process, various sounds are played back to the patient under computer control. Electrodes on the head can be used to measure the extent to which signals are transmitted via the cochlear nerve and whether they reach the brain. By measuring the conducted signals, it is possible to determine whether there is damage and conduction problem in the auditory nerve.
The advantage of this method is that it can be used independently of the patient’s subjective perception. This method is called BERA (brain stem electic response audiometry). Extended conduction times indicate damage.
On the other hand, the function of the vestibular organ can be checked. In this context, the extent to which a nystagmus can be triggered is investigated. A nystagmus is a jerky movement in the eye that is controlled by reactions in the organ of equilibrium.
One can easily perceive this process oneself in a moving train. The eye fixes an object and moves quickly in the direction of travel when the object disappears and fixes a new object. This nystagmus can be triggered artificially when the ear is rinsed with warm fluid.
Then a separate part of the organ of equilibrium, one of the archways, becomes irritated and causes a reflex-like eye movement. If the reaction fails at the eye or is different on the two sides, this is a good sign that there is damage to the organ of equilibrium. The movements at the eye are made visible to the patient by using Frenzel glasses.
These are glasses that the patient puts on, with very strongly refractive lenses that prevent the patient from fixing objects in the environment, which would falsify the result. A similar way of stimulating the organ of balance is to place the patient on a swivel chair and observe the eye movements, as well as after the abrupt stopping of the rotation. Frenzel Glasses are also used here to better represent the movements.
With both methods, failure and unexcitability of a nystagmus or the occurrence of a spontaneous nystagmus (without stimulus) indicate possible damage. Furthermore, the organ of equilibrium can be tested by various walking and standing attempts. The actual presentation of the acoustic neuroma, however, allows the MRI of the head (nuclear spin) with contrast medium.
In this process, the entire region in the area of the inner ear and cerebellar bridge angle can be depicted very precisely via very thin slices. Even very small tumours in the range of a few millimetres are noticeable here. The contrast medium can be used to make changes in the tissue clearly visible, since tumours, for example, have a different contrast medium absorption. Furthermore, a CT (computer tomography) of the skull can be made. Here they do not show the soft tissues as well as in the MRI of the head, but the bony surroundings can be shown well.