Acoustic Neuroma (Vestibular Schwannoma)
Causes and risk factors
The incidence is approximately one case per 100,000 population per year, but increases in patients with neurofibromatosis.
Which are the symptoms?
Symptoms depend on the size of the tumor and thus the progressive involvement of certain nerve structures:
- Symptoms associated with auditory nerve compression. Unilateral hearing loss, tinnitus, and loss of balance are the earliest symptoms that are almost always present at the time of diagnosis.
- Symptoms associated with trigeminal and facial nerve compression. Ear pain, impaired corneal reflex, facial nerve dysfunction, which usually occur when the tumor reaches more than 2 cm in size.
- Symptoms associated with brain stem compression. Large tumors (4 cm) may cause ataxia, nystagmus, diplopia, symptoms of cerebellar damage, and later mixed nerve dysfunction, obstruction of normal cerebrospinal fluid circulation and respiratory disturbances.
How is it diagnosed?
Diagnostic tests are magnetic resonance imaging (MRI) of the brain with gadolinium and computed tomography (CT), especially on bone-filtered images, to evaluate possible enlargement of the auditory canal, characteristic of neurinoma and usually absent in other lesions of the cerebellopontine angle that may be part of the differential diagnosis (especially meningioma).
How is it treated?
Essentially, there are two treatment options:
· Stereotactic radiosurgery using the Gamma Knife. It consists in an extremely precise concentration of gamma rays on the lesion site. In recent years, the therapeutic indications for the treatment of acoustic neuroma have changed considerably: until a few years ago, stereotactic radiosurgery was only offered to elderly patients or patients who had already undergone surgery with residual postoperative effects. With the development of technology (transition from computed tomography to magnetic resonance imaging, use of GammaPlan software) and a reduction in radiation dose, excellent results with extremely low complication rates have been obtained.
Therefore, the Gamma Knife is considered the treatment of first choice in all patients with auditory neuroma smaller than 3 cm, with no evidence of brain stem compression or risk of hydrocephalus. The risk of facial nerve dysfunction is less than 2-3%, and there is a good chance of preserving hearing if it was present before treatment.
· Surgical removal. Current surgical techniques allow a choice between different surgical approaches (retrosigmoid, translabial, extradural subtemporal) depending on the size and exact location of the neurinoma (intracanal or extracanal) as well as the possible neurological deficit found in the patient before surgery.