Acoustic neuroma (also: vestibular swannoma), a benign and mostly slow-growing tumor, which arises from the equilibrium nerve (nervus vestibularis) mostly within the bony auditory canal (Meatus acousticus internus), is one of the most common diseases in the area of the cerebellopontine angle.
Due to the slow increase in size and the suppressive growth, clinical symptoms often come very late. The vestibulocochlear nerve is first affected by the tumour’s site. Hearing loss, one-sided hearing deterioration, tinnitus and progressive dizziness are common symptoms.
Already with these symptoms, further diagnosis should be performed with electrophysiological examinations (AEP and BERA) and an MRI scan of the skull. In the AEP (Acoustic Evoked Potential) examination, the function of hearing is determined by means of acoustic signals. Brain stem audiometry (BERA) also tests hearing ability by measuring electrical brain currents. As the tumor grows, the adjacent cranial nerves of the cerebellum bridge angle are also pressed, leading to hypaesthesia (feeling numb) in the facial area, facial paresis (facial paralysis) and swallowing problems.
However, large tumors can reach as far as the brain stem or even overwhelm it. This, in turn, can lead to a rapid worsening with far-reaching neurological symptoms and a life-threatening situation, as a result of compression of the brainstem leads to a blocking hydrocephalus with increasing fluid build-up (fluids circulating within the central nervous system).
In order to decide on the best individual treatment strategy, a detailed, interdisciplinary diagnosis is necessary. This includes an in-depth medical history (history of the disease) and a thorough neurological examination as well as an apparatus diagnosis. This includes, in particular, the ENT medical examination using medical apparatus: audiogram, speech comprehension, as well as electrophysiological examinations allow an assessment of the functional impairment of the vestibulocochlear nerve (eighth brain nerve, which consists of the balance nerve and auditory nerve).
In case of an acoustic neuroma, a detailed neuroradiological imaging must always be performed in an MRI (“tube”). Thin-film MRI images (with a layer thickness of 1 mm or less with contrast medium, native and T2 as well as CISS special sequences) are required to represent the cranial nerves with different highlights. In addition, a thin-film CT of the base of the skull and the rock bone (a section of the temporal bone) is performed to assess the bony conditions.
Waiting checks on progress
Depending on the patient’s symptoms, regular clinical follow-ups with ENT medical examinations and regular MRI checks may be recommended for the initial diagnosis of small tumours. Elderly patients with increased risk of surgery may be encouraged to wait and scan if there is no evidence of rapid tumour growth, unless there is a strong impairment and there is no evidence of rapid tumour growth. However, for large tumours where there is a risk of brain stem compression (if the tumour is already crowding the brain stem), neurosurgical therapy should be used.
Minimally invasive tumor removal
In the area of the cerebellum bridge angle, i. e. between the brain stem, the cerebellum and the bone, very narrow anatomical conditions prevail. In addition, there is a very close proximity to the most sensitive neuronal structures. This is where the central parts of ten of the twelve cranial nerves are located.
The removal of tumours in this region is a neurosurgical challenge and requires specialization as well as many years of operating experience and expertise in the field of the skull base, as Prof. Feigl has. Using state-of-the-art instruments, Prof. Feigl uses for these operations, he is able to perform interventions at the base of the skull with minimal invasiveness via very small and gentle accesses (skull openings).
Due to the benign and slow growth of acoustic neuromas, conventional radiation is not effective. Here a high dose of precision irradiation, such as Gamma Knife or CyberKnife irradiation (radiosurgery), is necessary. The aim of this high-precision irradiation is to stop the growth of the tumor. Often the tumour can even be reduced a little with this method. As with conventional irradiation, however, the surrounding neuronal structures (which affect the nerve cells) must be outside the irradiation field, which is ensured by millimetre-precision planning.
Nevertheless, effective irradiation of the tumor edges is difficult. Such irradiation is not possible, especially in the case of large tumours and in the direct vicinity of the brain stem. In the case of relapses, a new radiation therapy is usually only possible to a limited extent. Surgical therapy is extremely difficult for pre-radiated tumors due to scarring of the tissue. Prof. Feigl performs radiosurgical treatment on his patients at the Cyberknife Centre Southwest in Göppingen. For more information, please visit https://www. radiochirurgicum. de/cyberknife-expertenteam. php.