Acoustic neuroma, also known as vestibular schwannoma, is a benign slow-growing tumor that develops on the vestibular branch of the vestibulocochlear nerve. The tumor arises from Schwann cells of the nerve traversing from the inner ear to the brain. The nerve’s main function is in hearing and balancing; therefore, the growing tumor can affect hearing and balancing along with other manifestations of the compression due to adjoining structures due to the tumor. Acoustic neuroma is caused due to malfunctioning of a gene on chromosome 22 that produces tumor suppressor protein to help control growth of Schwann cells of the nerve sheath. The etiology behind this aberration is still unknown. However, people with a genetic disorder, neurofibromatosis type 2 are at an increased risk of developing the tumor, accounting for approximately 5% of all cases of acoustic neuroma.(1)
Coping Methods For Acoustic Neuroma
The management of acoustic neuroma depends on the severity of symptoms that can range from mild to severe along with the size of the tumor. The various coping methods include careful observation, stereotactic radiation therapy and surgical excision of the tumor. Simple observation without any treatment is carried out in patients who are elderly, patients with small tumors, patients with increased risk of complications due to operation, a tumor on the only hearing side and in patients who refuse treatment. However, eventually, 15-40% of patients kept on observation eventually require treatment. Therefore, patients should be kept on observation after considering the preoperative hearing in both ears, increased risk of immediate hearing loss after surgery, risk of facial nerve paralysis due to surgery, risk of surgical complications, patient’s life expectancy, and size of the tumor, tumor growth rate and patients with neurofibromatosis type 2 with bilateral tumors.(2)
Stereotactic radiotherapy is an effective alternative to microsurgery for some acoustic neuroma patients. It can be used as a single dose or as multiple fractionated doses to deliver radiation at a precise point or to a series of points to maximize the amount of radiation. The radiation prevents the further growth of the tumor. However, stereotactic radiotherapy should not be performed in larger tumors and patients at an increased risk of hydrocephalus and disequilibrium.(2)
Surgical intervention is the treatment of choice for the removal of the tumor. It should be carried out on patients <65 years with medium to large tumors, growing tumors, significant hearing loss and those with severe headaches. The various approaches for the surgical extirpation of acoustic neuroma include retrosigmoid, translabyrinthine and middle fossa approaches. Retrosigmoid approach cannot be used in small tumors that are located far away in the internal auditory canal. Hearing conservation surgery can be attempted even for larger tumors. The consideration of various approaches depends on the preoperative hearing level, auditory brainstem response, tumor size, tumor location, relevant anatomy, surgeon’s preference and patient’s preference of hearing preservation or facial nerve preservation.(2)
Vestibular rehabilitation is necessary postoperatively in some patients with either contralateral routing of signals (CROS) or bone-anchored hearing aid (BAHA). It is also important to follow up for an MRI to determine the completeness of tumor removal. The outcome of acoustic neuroma has drastically improved over the years with preservation of hearing in about 30-80% cases.(2)
Presentation Of Acoustic Neuroma
Since acoustic neuroma is a slow-growing tumor, the signs and symptoms of the tumor take years to develop. They occur due to the effect of the tumor on the vestibulocochlear nerve and the adjoining facial nerves (trigeminal and facial nerve), blood vessels and brain structures. The most common symptom of acoustic neuroma includes unilateral progressive hearing loss, which can be sudden on rare occasions. Tinnitus is another common symptom associated with hearing loss. The other symptoms include loss of balance or a feeling of unsteadiness, dizziness (vertigo), facial numbness, facial weakness or facial paralysis. The compression of the brainstem due to a large acoustic neuroma can lead to fluid build-up in the skull, known as hydrocephalus that can have life-threatening complications if not managed immediately.(1)
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