A slow growing brain tumour, such as an acoustic neuroma, develops over years, and often over decades, and correspondingly often causes only a few complaints during this long time period.
Given that an acoustic neuroma grows on the nerve sheath of the nervus vestibulocochlearis (cranial nerve VIII with a balance and acoustic part), the first disorders affect an acoustic neuroma sufferer's balance and hearing.
The most frequent and common first symptom is a decrease in hearing on one side. In most cases the loss of hearing occurs slowly and subtly. Those affected often notice the hearing problem very late or by chance, for example when telephoning or during a routine examination. Above all, high-frequency hearing difficulties are noticed – suddenly one can no longer hear the birdsong or it has changed. Acoustic neuromas are often noticeable through acute hearing loss, in other words through a sudden onset, on one side, of almost complete hearing loss. In many cases improvements or corrections of hearing loss are seen after several days of infusion treatment with blood circulation enhancing agents. However, it is not permanent. At a later stage further acute hearing losses occur and the patient's hearing becomes increasingly poor. Several losses of hearing mostly indicate an acoustic neuroma.
The increasing hearing difficulties are often accompanied by ear noise, or tinnitus; tinnitus may even be the first symptom, without the person affected having or experiencing hearing loss. Like hearing loss, tinnitus is also present mostly in the high-frequency range. Most of those affected find it has a severe impact.
Although acoustic neuromas mostly originate from the upper part of the balance nerve, vertigo and impaired balance rank only in third place as a symptom of an acoustic neuroma. They appear as swaying dizziness, and seldom as vertigo and unstable walking. Often only after being asked directly do acoustic neuroma sufferers admit to experiencing an occasional vague feeling of instability, mostly in the dark and with sudden head and body movements. The causes for the late subjective feeling is that acoustic neuromas mostly grow very slowly and the brain is in the position, based on the intact system on the other side of the head , to compensate for the failing balance system. A pleasant consequence of this, amongst others, is that after an operation there are no longer any noteworthy balance problems.
These three complexes of symptoms already occur when the acoustic neuroma is still relatively small and it is found mainly or exclusively in the bony ear canal (in the intrameatal position). In this narrow, bony area the facial nerve is often pressed flat, however it still retains its function. Through the slow loss of the balance function the brain can offset the functions of the balance system. However, the auditory nerve reacts most sensitively to disorders (compression and reduced blood supply). For that reason hearing impairments are most commonly the first symptom.
An acoustic neuroma growing towards the skull base can interfere with the functions of other cranial nerves and vessels, which supply the brain and lead into the brain through the openings in the skull base.
If the 7th cranial nerve (nervus facialis) is impaired this leads to motor failures in the face, as this nerve is responsible for facial muscles, amongst other things. Facial paralysis or facial palsy are referred to here. With severe damage, the production of tear fluid and secretions from the nose and palate are affected. Eventually, the sense of taste in two thirds of the tongue will also suffer.
If the 5th cranial nerve (nervus trigeminus) is impaired this leads to sensation problems or facial pain. We're referring here to trigeminal neuralgia. The trigeminal nerve is also responsible for the jaw muscles. These symptoms occur less frequently because this cranial nerve passes somewhat further away from the cerebellopontine angle.
It is similar with the 9th cranial nerve (nervus glossopharyngeal) and 10th cranial nerve (nervus vagus). Impairments to these nerves lead to problems swallowing, painful swallowing and taste disorders in the rear third of the tongue, amongst other problems.
You can read more about the cranial nerves in the skull base region here:
Cranial nerves and skull base surgery.
Source: University Hospital Tübingen (german)
At the latest stage, the term «benign tumour» is absurd, when the acoustic neuroma has become so big that it fills the «reserve space in the brain», the cerebellopontine angle , and it presses on the cerebellum and the brainstem. These are areas that have vital functions for life for coordinated movement (cerebellum), breathing, heart and circulation as well as protective reflexes and the wakefulness function (brainstem). If the acoustic neuroma has become so large that it occludes the outflow of cerebral fluid (CSF) in the cerebellopontine angle and dams the cerebral fluid in the brain, the pressure in the head increases (occlusion hydrocephalus). Symptoms of this are: impaired movement coordination, severe walking difficulties and prone to falling, headaches at the back of the head, neck stiffness, vomiting, vision disorders, cognitive disorders. The lateral pressure on the brainstem can eventually lead to heart and circulation disorders, which can be life-threatening – and this is all without metastases!
The abovementioned symptoms occur differently in patients – at different times, in different intensities, in different orders and in different combinations. The causes of this are the different sizes and positions of acoustic neuromas, e.g. further into the rear skull cavity or still in the inner, bony ear canal. The size and position determine how severely the cranial nerves will be affected. Thereby, the position of the tumour is at least as important as its size.
Given that some symptoms can have causes other than an acoustic neuroma, it is not possible to diagnose an acoustic neuroma solely on the basis of these symptoms. However, specifics such as several occurring acute hearing losses and a combination of two or more symptoms must be evaluated by responsible doctors as a possible indication of the presence of an acoustic neuroma brain tumour. The introduction of a more targeted diagnostic procedure must then follow. It should not remain as it is, as some of the symptoms mentioned are still dismissed as «age-related» complaints or as a consequence of work-related or personal stress!
It is important that a small acoustic neuroma, as a rule, may still not cause any of the abovementioned later symptoms and can be treated successfully. Early detection of symptoms and their conscientious analysis and interpretation are therefore a priority for doctors. Acoustic neuroma patients can contribute greatly to this through good observation of their sensations and complaints.