What is Acoustic Neuroma?
An acoustic neuroma is a type of tumor also known as vestibular schwannoma, acoustic neurinoma, vestibular neuroma, and acoustic neurofibroma. These tumors come from the Schwann cells that wrap the vestibular and cochlear nerves, which are involved in hearing and balance, respectively. Acoustic neuromas can develop inside or outside the brain.
Most commonly, acoustic neuromas are found at the cerebellopontine angle, which is near the cochlear and vestibular nerves, especially the lower section of the vestibular nerve. Between 5% to 10% of tumors at this location are called meningiomas, which can also appear in other parts of the brain. Most acoustic neuromas happen randomly, but when there are acoustic neuromas on both sides, it’s usually linked to a condition called type 2 neurofibromatosis.
What Causes Acoustic Neuroma?
Acoustic neuromas, which can occur on both sides of the brain, may be connected to a condition known as neurofibromatosis type 2. This is due to a genetic flaw on chromosome 22q12.2, which affects the merlin protein. This protein is produced by the neurofibromin 2 gene and research has suggested a connection between a mutation here and the development of acoustic neuroma. Exposure to radiation may also raise the chances of getting this condition.
There have been worries about the radiation produced by mobile phone usage being a cause, but so far, multiple studies have not found solid evidence to suggest that mobile phone radiation directly leads to the growth of this type of brain tumor, known as vestibular schwannomas.
Risk Factors and Frequency for Acoustic Neuroma
Schwannomas, accounting for roughly 8% of all brain tumors that exhibit symptoms, are more often than not, unilateral and occur randomly. But, sometimes they can occur on both sides due to genetic factors, though such cases are less than 5% of all schwannomas.
Typically, acoustic neuromas, a type of schwannoma, are detected between the ages of 40 to 60. But people with a condition known as neurofibromatosis type 2 (NF II) generally see symptoms earlier, most commonly in their 30s. While it’s rare, children can also have acoustic schwannomas.
They’re slightly more common in women, and symptoms can intensify during pregnancy. The hereditary form of acoustic neuromas is commonly linked to NF II. This is despite the condition, neurofibromatosis type 1 (NF I), being more common overall. NF I is associated with unilateral acoustic neuromas in 24% of cases, while NF II is characterized by bilateral acoustic schwannomas. Both NF I and NF II are inherited in a way that a single copy of the altered gene in each cell is sufficient to cause the disorder, with genetic defects found on chromosome 17 and chromosome 22, respectively.
Signs and Symptoms of Acoustic Neuroma
An acoustic neuroma is a condition primarily caused by a tumor pressing on the parts around it, including several cranial nerves, the cerebellum, the brainstem, and increasing the pressure inside the skull. It often leads to hearing loss, ringing in the ears, decreased understanding of spoken words, dizziness, headaches, and numbness. As the tumor grows, it can affect walking due to pressure on the brainstem. Below, we discuss in detail the clinical features of an acoustic neuroma.
The clinical symptoms of an acoustic neuroma relate to its effect on various parts of the brain:
- Effects on Cranial Nerve VIII (the Auditory and Vestibular nerve):
- Hearing loss is the most common symptom, usually slow and unnoticed at first.
- Tinnitus, or a constant or intermittent ringing or buzzing sound in the ears, may occur.
- Problems related to the body’s balance system can include feeling unsteady when moving the head and “nystagmus,” a condition causing involuntary eye movements.
- Effects on other Cranial Nerves:
- The Facial nerve: Symptoms can include facial twitching, lachrymation (increased tearing), and weakness in the face.
- The Trigeminal Nerve: Symptoms can include tingling and numbness in the face, and sometimes even pain similar to trigeminal neuralgia.
- The Glossopharyngeal and Vagus nerves: Symptoms can include weakened palatal muscles, a hoarse voice, and difficulty swallowing.
- Effects on the cerebellum (large tumors only):
- Unsteady walk, coordination and balance difficulties, hand tremors, and fine motor skill problems. Rarely, speech problems may also occur.
- Effects on the brainstem:
- Pyramidal weakness, involvement of cranial nerves on the opposite side, and nystagmus.
- Raised intracranial pressure:
- Headache, nausea, vomiting, rise in blood pressure, decreased mental abilities, confusion, altered consciousness, and papilledema (swelling of the optic disc due to increased pressure within the skull).
Testing for Acoustic Neuroma
If your doctor suspects you have an acoustic neuroma, which is a type of brain tumor, they will use a detailed imaging technique like an MRI or CT scan to diagnose it. These tests involve the usage of something called a contrast agent, in this case, usually gadolinium, to help make the image clearer. This doesn’t just make the tumor more visible, it also gives your doctor information about what the tumor looks like and where it’s located in your brain. The use of contrast is especially important when looking for smaller tumors.
If you are showing signs of hearing loss, your doctor may also want to check your hearing ability using various tests. However, the auditory brainstem evoked response test, although helpful, isn’t typically used as the primary screening tool for these tumors since it might not reliably detect smaller ones.
Sometimes, an acoustic neuroma might cause characteristic signs on an imaging scan. For instance, if the tumor is in the porus acusticus, it can cause a clear sign called the “trumpeted internal acoustic meatus,” which looks like a widening or enlargement of the opening. Alternatively, a tumor extending into the extrameatal space can cause the “ice cream cone” sign.
On an MRI scan, acoustic neuromas usually appear lighter or of similar intensity on one type of image (T1-weighted), and demonstrate heterogeneously brighter intensity on another type (T2-weighted image). Furthermore, when gadolinium, the contrast agent is administered, these tumors often show up as particularly bright. Lastly, your doctor might use a particular type of MRI called fast spin-echo as a screening test for acoustic neuromas, due to its lower cost and being noninvasive.
Treatment Options for Acoustic Neuroma
Acoustic neuromas, a type of tumor in the ear, can be treated in several ways depending on how large they are and how much they’re affecting a person’s health.
Firstly, if the tumor is small and isn’t causing serious symptoms, doctors may choose to simply keep an eye on it and see if it grows. This approach is also often chosen for elderly patients who have various other health conditions.
Secondly, another option could include stereotactic radiotherapy. This treatment involves using high-energy radiation to kill the tumor cells. Methods referred to as Gamma Knife or Cyberknife are precise forms of this radiation therapy that are most widely used.
Lastly, another treatment option might be surgery, particularly for larger tumors or those causing discomforting symptoms.
There are three main types of surgical approaches to treat acoustic neuromas:
1. The Retrosigmoid approach: This involves removing the tumor by creating an opening at the base of the skull. This option is helpful as it provides good access to the tumor and nerves in the brain. This method can be used on tumors of any size while potentially maintaining the hearing ability.
2. Middle cranial fossa approach: Here, the surgeon reaches the tumor through the middle of the skull base. It’s a suitable option for tumors that are primarily inside the ear canal and have a small exterior extension. In most cases, this approach tends to preserve hearing. The key disadvantage is that it might require moving aside the temporal lobe of the brain during surgery, which may result in post-surgery seizures and venous infarction if a vein located in the brain gets damaged.
3. Translabyrinthine approach: This entails removing the tumor via the inner ear. It is often used for patients with large tumors and who have already lost their hearing. The main advantage of this approach is it allows early exposure and protection of the facial nerve, and it doesn’t require the cerebellum to be moved aside. However, this approach does limit access to the jugular foramen and the lower parts of the large opening at the base of the skull.
After surgery, an MRI scan is needed within 6 to 12 months to check how much of the tumor has been removed and to establish a reference image for future check-ups. Common issues after the surgery may include injury to the anterior inferior cerebral artery, hemorrhage, trauma to the cerebellum, facial paralysis, hearing loss, and hydrocephalus or buildup of fluid in the brain.
What else can Acoustic Neuroma be?
Acoustic neuromas (growths on the main nerve from your inner ear to your brain) represent about 80% to 90% of what doctors call CPA lesions in the medical field. But, there are other conditions that need to be considered when diagnosing an acoustic neuroma. These conditions and their characteristics are listed below:
- Meningioma: This is an uncommon type of tumor that grows from the membranes surrounding the brain and spinal cord. These account for 5% to 10% of CPA lesions.
- Ectodermal inclusion tumors, epidermoid cysts, and dermoid cysts: These are largely benign (non-cancerous) cysts.
- Metastases: This term refers to cancer spreading from one organ to another.
- Neuromas from cranial nerves other than the eighth cranial nerve, including trigeminal neuroma (a tumor on the fifth cranial nerve), facial nerve neuroma (a tumor on the seventh cranial nerve), and neurinomas of the last four cranial nerves.
- Various potential nearby issues in the CPA region, including aneurysms, brainstem or cerebellar glioma (brain tumors), pituitary adenoma (hormone-related tumors), and others.
- Choroid plexus papilloma (an abnormally growing structure in the brain), glomus jugulare tumor (a tumor at the base of the skull), and tumors of the temporal bone (a region of the skull).
A doctor will carefully consider these and other possibilities to determine the best method of treatment.
Possible Complications When Diagnosed with Acoustic Neuroma
Most issues that occur during or after surgery are related to the procedure itself. These can include:
- Injury to the arteries near the cerebellum (the part of the brain at the back of the skull)
- Neurological injury
- Brain herniation (when the brain shifts out of its normal position)
- Bleeding in the brain
- Injury to the cerebellum
- Facial paralysis
- Hearing loss
After surgery, around 10% to 20% of patients may experience tinnitus, which is a ringing or buzzing in the ears. The likelihood of the problem returning even after removal is less than 5%. Facial paralysis, though it happens in about 15% to 30% of patients, usually resolves itself over time. Over half of the patients may experience hearing loss, which may not get better. This persistent hearing loss can greatly affect the quality of life.
Recovery from Acoustic Neuroma
Patients who have undergone surgery, or those who haven’t, often experience dizziness and balance problems, which can be improved through certain exercises. These exercises aim to help the brain adapt, substitute, and become accustomed to changes and include exercises like looking stability, repeated movements based on the movements that cause symptoms, and controlling sight or moving the eyes and head towards different targets.
Following surgery for a specific type of tumor called an acoustic neuroma, patients may face side effects like facial paralysis. Thankfully, rehabilitation techniques exist to manage these issues and help patients regain their normal function. Techniques that can be used include mirror therapy and imagining movements.
Rehabilitation programs focusing on balance and coordination should be customized to address a patient’s specific problems. Research has shown that this targeted approach is more beneficial for patients than a one-size-fits-all program.
