Acoustic Neuroma and Hearing Changes

Acoustic neuromas affect about 10 out of every one million people with more women than men being affected. An acoustic neuroma is a slow growing, non cancerous tumor that that arises from the nerves involved in balance and hearing. It is more appropriately known  as vestibular schwannoma and grows from the Schwann cells forming the outer covering of the vestibulocochlear nerve (eighth cranial nerve). As this benign tumor grows, it expands out of its original location inside the internal auditory canal and out into the space between the brainstem and the bone, thereby displacing the cochlear, facial and trigeminal nerves located in the cerebellopontine angle. As this pear-shaped tumor enlarges, it compresses the brainstem.

As it’s a slow-growing tumor, with time, the tumor can lead to gradual hearing loss, ringing in the ears, dizziness as well as loss of facial sensation. Due to their slow growth however, not all acoustic neuromas need to be treated. The symptoms caused by the tumor are proportional to the size of the tumor with small tumors being less than 1.5cm, medium-sized ones being 1.5-2.5cm and large ones being over 2.5cm. These neuromas do not invade and destroy surrounding tissues as seen in cancerous tumors; their pathology is limited to the effects of compression and pressure exerted by the growing tumor’s mass.

However, their growing mass can create pressure on localized structures leading to life-threatening situations. Compression of the brain stem can become severe enough in some cases to lead to fourth ventricular compression resulting in hydrocephalus with persistent headaches, visual problems and unconsciousness. As the tumor enlarges in size, it causes severe compression on the facial, trigeminal and lower cranial nerves. Considering the extent of complications, an earlier diagnosis makes for better management options and lower morbidity.

Diagnosis is usually based on a neurological examination; this includes checking for sight, hearing, smell, tongue and facial muscle movements, muscle strength, coordination and reflexes, mental status and response to pain. Some of the diagnostic tests used include an Audiogram, which is essentially a test to determine whether you have hearing loss and if it’s from nerve damage or from eardrum damage. Another test is Electronystagmography which evaluates your balance by monitoring eye movements while stressing balance in various ways. MRI and CT scans are two non-invasive tests that are used to get detailed information of the anatomical structures and soft tissues of the brain. They are especially useful in viewing changes in the bony structures such as the presence of tumors, lesions, changes in the brain structures and widening of the internal auditory canal.

Treatment options are dependent on the size of the tumor and include observation, surgery and stereotactic radiosurgery. Treatment also depends on the age of the patient, general health, hearing status and tumor size with larger tumors requiring more complex therapies. Tumors less than 3-3.5 cm can be treated with radiosurgery however the tumor will need to be monitored with MRI for many months following that. Microsurgcial excision of the tumor with intra-operative nerve monitoring (https://www.sbshospital.com/tech-talk-intra-operative-neurophysiologic-monitoring/) offers the best chance of a cure with low morbidity and mortality rates and a high degree of functional nerve preservation of the facial nerve. It’s therefore essential that the condition is recognized early and treatment initiated in a timely manner.

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