Acoustic neuroma or vestibular schwannoma is a benign tumor (not cancerous!) that develops on the nerve that connects your inner ear to the brain. We wanted to write about this topic because many patients think that it is brain cancer.
It is usually a slow-growing tumor that, although non-invasive, can compress various structures in the brain if it grows out of control. The main functions most commonly affected are the hearing, balance and facial expressions. The growth itself presents on the eighth cranial nerve which is the main nerve connecting the inner ear with the brain. It arises from the Schwann cells, a type of cells covering the nerve.
The eighth cranial nerve, known as the vestibulocochlear nerve, consists of two divisions; the vestibular and cochlear ones. The cochlear division is responsible for hearing while the vestibular division for balance. An acoustic neuroma will develop on the vestibular division, primarily affecting balance but may affect hearing too by pressing the cochlear division.
It is not considered a prevalent tumor as only one in 100,000 will develop acoustic neuroma in the US. Although any age group can present with acoustic neuroma, people between 40 and 50 years old are more prone to it.
In general, there are two forms of acoustic neuroma:
- A sporadic form, being the most common.
- A type associated with neurofibromatosis type II, accounting for just 5% of acoustic neuromas.
Although the exact cause of acoustic neuroma is unknown, what is common in both forms is a gene defect on chromosome 22. This gene, under normal circumstances, suppresses any abnormal growth of the Schwann cells.
Acoustic Neuroma Causes And Symptoms
Acoustic neuromas are usually silent in the beginning. Early symptoms are subtle and may be attributed to common aging. As a result, acoustic neuromas are diagnosed when they have already been essentially symptomatic. The first and most common symptom is gradual and unilateral hearing loss. Hearing loss may be accompanied by a ringing sensation in the ear known as tinnitus, together with a sensation of ear fullness.
Other symptoms that may appear are relevant to the pressing properties of the tumor and they are:
- Balance issues, due to compromised function of the eighth cranial nerve
- Vertigo, commonly known as dizziness, due to compromised function of the eighth cranial nerve
- Persistent or intermittent facial numbness and tingling, due to facial nerve involvement
- Weakening of the facial muscles, due to facial nerve involvement
- Taste disturbances, due to other cranial nerves involvement
- Swallowing difficulties, due to other cranial nerves involvement
- Hoarseness of the voice, due to other cranial nerves involvement
- Headache, due to pressing properties of the tumor
- Unsteadiness, due to pressing properties of the tumor
- Confusion, due to pressing properties of the tumor
Usually, the nature of the symptoms indicates the severity of the condition. Some symptoms appear in the early stages of the disease while others in later and potentially urgent ones. For example, hearing loss and tinnitus may represent early symptoms while clumsiness and confusion may indicate an emergency that requires immediate treatment. Whatever the case, medical consultation should take place, regardless of the severity of the symptoms.
What are the risk factors for Acoustic Neuroma?
The main risk factor for Acoustic Neuroma is neurofibromatosis type II. At the same time, the main risk factor for Acoustic Neuroma is having a first-degree family history with the disease, which is genetic. Neurofibromatosis type II presents with benign tumor formations on various nerves of the body. What causes neurofibromatosis type II is a gene defect on chromosome 22.
Process of Acoustic Neuroma Diagnosis
Acoustic Neuroma may be difficult to diagnose due to the absence of early and concrete symptomatology. However, diagnosis is established with history taking and clinical investigations. History taking is the process of asking questions to form a picture regarding the patient’s subjective symptoms. After history taking is complete, a hearing test, known as audiometry, should be performed. The hearing test will determine whether there is a hearing compromise or not. Finally, imaging will determine the presence or absence of an acoustic neuroma. The two most common imaging methods used to diagnose an acoustic neuroma are magnetic resonance imaging (MRI) and computerized tomography (CT), the former being more efficient.
Acoustic Neuroma Prevention
There is no known preventive strategy for acoustic neuroma. However, one could prevent complications. Some of the permanent complications of acoustic neuromas are the following:
- Hypoacusis, known as hearing loss
- Facial numbness and weakness, due to facial nerve injury
- Tinnitus, known as ringing sensation in the ear
- Hydrocephalus, known as a fluid collection in the brain due to brainstem compression
In general, preventing the complications of acoustic neuroma means diagnosing it early and treating it efficiently.
How to treat Acoustic Neuroma?
An acoustic neuroma can be managed accordingly, depending on its size and properties. While some acoustic neuromas may just need to be observed over time through imaging, others may require surgery or radiation therapy.