Findings explain, why some vestibular schwannomas cause hearing loss even though they are not large enough to compress nearby structures that control hearing.
A study carried out at Massachusetts Eye and Ear in the US has shown that in some cases of vestibular schwannoma, secretions from the tumour contain toxic molecules that damage the inner ear. Vestibular schwannoma is also known as acoustic neuroma.
Tumour compresses the auditory nerve
"What's written in textbooks is that these tumours (vestibular schwannoma) cause hearing loss by growing to the point of compressing the auditory nerve," said senior author Konstantina M. Stankovic, M.D., Ph.D., FACS, an otologic surgeon and researcher at Mass. Eye and Ear.
"We knew that it couldn't be as simple as that, because there are large tumours that do not cause hearing loss and little ones that do."
The researchers also identified TNFa, a toxic compound that has been implicated in other forms of hearing loss, as a causative toxic molecule in the secretions from human vestibular schwannomas. When they applied those secretions directly to a mouse cochlea, they found that the degree of cellular damage correlated to the severity of hearing loss in humans.
Hearing loss often the first sign
Hearing loss is often the first sign of a vestibular schwannoma. Vestibular schwannomas grow from the Schwann cells of the vestibular (balance) nerve in the inner ear and represent the fourth most common intracranial tumour.
Although histologically non-malignant, vestibular schwannomas growing in size can damage nearby structures and can lead to death by compressing the brainstem. By compressing nerves in the internal auditory canal, the tumours can cause vestibular dysfunction, facial nerve paralysis and sensorineural hearing loss. The study introduces a second way in which the tumours can cause sensorineural hearing loss, by secreting toxic molecules.
Hope for new treatment
Currently, patients with symptomatic or growing vestibular schwannomas can undergo surgical resection or radiotherapy; however, both of these procedures can result in serious complications.
"Because these are histologically non-malignant tumours, they do not need to be removed or irradiated as long as they are not growing. However, hearing can continue to decline even in patients with non-growing tumours," Dr. Stankovic said.
"Our findings suggest that there may be a pharmacologic way to maintain hearing in some patients with vestibular schwannoma."
The study was published online in Scientific Reports.
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