Acoustic neuroma, also referred to as vestibular schwannoma, is a benign, generally slow-growing tumor that develops in the vestibulocochlear nerve (8th cranial nerve). Acoustic neuroma usually arises from the Schwann cells (cells that form an insulating layer around the nerve fiber) covering the vestibulocochlear nerve and either grow slowly or not at all. Rarely will it grow rapidly and become large enough to press against the brain and interfere with vital functions.
This tumor constitutes 8% of all intracranial tumors, with an incidence from 1 to 20 per million per year. The majority, 95%, of acoustic neuromas are unilateral and sporadic. Bilateral acoustic neuromas are genetic and constitute less than 5% of all schwannomas. Acoustic neuromas tend to present themselves between the fourth to sixth decades of life. Acoustic neuromas developing in individuals with neurofibromatosis type 2 (NF 2) are likely to present themselves earlier, with a peak incidence around the third decade of life. Although rare, acoustic schwannomas can occur in children. There is a slight female preponderance for the occurrence of acoustic neuromas.
The symptoms of acoustic neuroma are dependent on the location, size, and growth of the tumor. The signs and symptoms of acoustic neuroma are attributed to the involvement of cranial nerve VIII, compressing surrounding cranial nerves, cerebellum, and brainstem, as well as raised intracranial pressure. Following are some symptoms:
Balance and hearing problems are caused by the branches of the vestibulocochlear nerve which are directly influenced
Pressure from an acoustic neuroma can cause hearing loss (partial/complete), tinnitus (ringing in the ear), and unsteadiness
As the tumor expands, hearing loss may worsen, along with balance problems (disequilibrium), nystagmus (involuntary, rapid, repetitive eye movement), and facial weakness may occur. Large tumors can also compress the brainstem (causing imbalance) and the trigeminal nerve (causing facial numbness).
A diagnosis of an acoustic neuroma is made based upon a thorough clinical evaluation, a detailed patient history, identification of characteristic findings, and a variety of specialized tests. Diagnostic tests may include hearing examination, a specialized test that evaluates balance (electronystagmography), a brainstem auditory evoked response (BAER), scans such as computed tomography (CT), and magnetic resonance imaging (MRI). Due to better diagnostic tools and increased awareness of the disease, patients with acoustic neuroma may be diagnosed earlier and receive early therapy.
The treatment of acoustic neuromas is carried out by a multidisciplinary team of experts; including neuro-otologists (ear, nose and throat, and hearing surgeons), neurologists, neurosurgeons, neuro-oncologists, radiation oncologists, radiologists, hearing specialists (audiologists), physical therapists and also other specialists may be involved in the care. There is no single, “best” therapy for all affected individuals. The specific location and size of an acoustic neuroma as well as an affected individual’s overall level of hearing and general health are all considered when determining the preferred treatment method. However, due to their slow growth, not all acoustic neuromas need to be treated.
Treatment options include observation, surgery, and radiotherapy. Surgical resection/microsurgery remains the primary treatment that can provide the greatest chance of a long-term cure, especially for large, symptomatic tumors. Various surgical approaches can be used to remove acoustic neuromas which include: retrosigmoid or suboccipital (through the skull behind the ear), translabyrinthine (through the inner ear), and middle cranial fossa (through the skull). Each of these surgical approaches has advantages and disadvantages that must be considered in selecting an optimal approach. In recent years, an increasing number of studies regarding stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) have established these techniques as safe, efficient, and minimally invasive alternatives. These advancements will improve the quality of life of the patients.