Acoustic neuroma is a benign slow-growing tumor of the vestibular portion of the eighth cranial nerve. The tumor arises from the Schwann cells of the peripheral nerve sheath; therefore, it is also known as vestibular schwannoma. The eighth cranial nerve runs from the inner ear to the brain and its main function is related in hearing and equilibrium. Unilateral hearing loss is found in approximately 90% of the cases of acoustic neuroma. Acoustic neuroma is seen in adults between the ages of 30 and 60 years of age and it is more prevalent in females than males. Acoustic neuroma affects 1 in 100,000 individuals and the incidence is steadily on an increase and approximately 2500 new patients are diagnosed every year.(1)
Who Is At Risk For Acoustic Neuroma?
The cause of acoustic neuroma is still not clear. Although there are no specific risk factors for acoustic neuroma, there are various potential risk factors for developing an acoustic neuroma. These include prior radiation to the head and neck region needed for the treatment of cancers, prolonged exposure to loud noises. People with the genetic disorder, neurofibromatosis type 2 may be at risk of developing an acoustic neuroma. However, in these patients, the acoustic neuroma is generally bilateral instead of occurring unilaterally.(1)
Is There A Blood Test For It?
Since, acoustic neuroma affects the eighth cranial nerve, routine laboratory testing, and blood testing is not required. The confirmatory diagnostic testing for the detection of acoustic neuroma is magnetic resonance imaging (MRI). Imaging is very sensitive as tumors as small as 1-2 mm in diameter can also be noted. CT scan is not as sensitive as a gadolinium-enhanced MRI as it can miss a large tumor measuring 1.5 cm even. non-enhanced MRI can also miss small tumors without gadolinium enhancement. However, MRI is contraindicated in people with ferromagnetic implants. In these cases, CT scan can be used with contrast for the detection of medium to large-sized tumors, but their role in the an of tumors smaller than 1-1.5 cm is questionable. In such cases, air-contrast cisternography can be utilized for the detection of smaller tumors.(2)
Immunohistochemical staining can be used to distinguish difficult cases of acoustic neuroma from meningiomas. While an acoustic neuroma is immunoreactive for S-100 antibody, meningioma is immunoreactive to epithelial membrane antibody (EMA).(2)
Treatment Of Acoustic Neuroma
Acoustic neuroma is managed either with careful monitoring, surgical excision or stereotactic radiation therapy. Monitoring is done in elderly patients, small tumors, increased risk of operation, tumor on the side of effective hearing and in those who refuse treatment. Stereotactic radiotherapy has emerged as an effective alternative to microsurgery that helps in the preservation of hearing for at least short term and decreased immediate post-treatment morbidity and mortality. Surgical therapy is the treatment of choice for patients <65 years of age, medium to the large-sized tumor, growing tumors, significant hearing loss and in patients with severe headaches.(2)
Symptoms Of Acoustic Neuroma
The symptoms of acoustic neuroma are due to compression of the nerve due to the tumor and disruption of nerve signal transmission. Small tumors can be asymptomatic; however, depending on their location can present with symptoms. Progressive and gradual hearing loss of unilateral side is the most frequent symptom. Tinnitus (ringing in the affected ear) is another common symptom. Acoustic neuroma can also cause dizziness and balancing problems, such as unsteadiness.(1)
Most of the times it is slow growing; however, at times the tumor may grow large enough to compress the adjacent nerves. This may lead to facial weakness, numbness, tingling, palsy, and dysphagia. At other times, a large acoustic neuroma may compress brainstem causing hydrocephalus (increased pressure in the brain) that may lead to headaches, ataxia, and mental confusion. In very rare occasions, an acoustic neuroma can lead to, complications.(1)
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