What is Vestibular Schwannoma?
Schwannomas, also known as neuromas, neurinomas “of Verocay,” and neurilemmomas, are non-cancerous, enclosed, and slow-growing lumps that form on the protective layer of nerves which is made up of Schwann cells originating from the neural crest. These cells are part of the nervous system and can be found in any nerve that’s insulated with a protective coat of myelin, whether it’s in the central nervous system (brain and spinal cord) or peripheral nerves (nerves outside the central nervous system).
The World Health Organization identifies schwannomas as a benign, or non-cancerous, tumor. They typically occur as a single tumor in about 90% of the cases. However, if a person has multiple schwannomas, it might be an indication of certain associated syndromes or conditions, like neurofibromatosis type 2, schwannomatosis, and Carney complex.
What Causes Vestibular Schwannoma?
Around 90% of schwannomas, which are usually noncancerous tumors that grow on the coverings of nerves, occur randomly without any specific cause or pattern. However, there are certain syndromes like neurofibromatosis type 2, schwannomatosis, and Carney complex where schwannomas might be linked to a person’s genetic makeup. This genetic link is not just limited to schwannomas related to these syndromes but might also be found in random, or sporadic, cases. Among these syndromes, neurofibromatosis type 2 is associated with 3% of the cases, schwannomatosis with 2%, and meningiomatosis, which can occur with or without neurofibromatosis type 2, with 5%.
Genetic research has found that a gene named NF2 on chromosome 22 plays a significant role in the development of both sporadic and syndrome-associated schwannomas. The NF2 gene is responsible for producing a protein called merlin. Changes or mutations in the NF2 gene result in turning off this gene’s function, preventing the production of merlin. It has been observed that both copies of the NF2 gene get turned off in most schwannomas. Carney complex might also be associated with the loss of function of a gene called PRKAR1A.
Further, spinal schwannomas can be associated with changes and loss of function in a gene called SMARCB1.
Risk Factors and Frequency for Vestibular Schwannoma
Schwannoma is the most common type of nerve sheath tumor, making up about 89% of all cases. These generally develop in people between the ages of 50 and 60, and can occur in anyone, regardless of gender or race. The tumors are usually found in the upper limbs, though they can also appear in areas like the head, trunk, lower extremities, and various internal organs like the liver or adrenal glands.
According to the Central Brain Tumor Registry in the U.S., non-malignant nerve sheath tumors make up 8.6% of all central nervous system tumors reported. There is an equal likelihood for any gender to develop these tumors, though they are more commonly seen in white individuals. The median age at diagnosis is 56 years with an incidence of 4.4 to 5.23 cases per 100,000 adults each year. In children and adolescents however, the rate is much lower, at 0.44 cases per 100,000 each year. The incidence of malignant nerve sheath tumors is considerably lower, at 0.03 cases per 100,000 each year.
Vestibular schwannomas specifically, have an incidence of 1.2 cases per 100,000 each year in the U.S., with the median age of patients being 55 years. These rates are similar in males and females, though the incidence is higher in Whites than non-Whites. In Denmark, the incidence rate of vestibular schwannomas is higher, at 3.4 cases per 100,000 each year, with the average age at diagnosis being 60 years.
Spinal schwannomas are less common, with an incidence of 0.24 cases per 100,000 each year. These are more commonly found in white males, typically affecting those between the ages of 65 and 74.
Signs and Symptoms of Vestibular Schwannoma
Schwannomas is the name for tumors that grow slowly, often going unnoticed for many years because they cause no symptoms. These tumors can be found in various parts of the body, which is why the symptoms can differ greatly. When a doctor touches the tumor, the patient may feel pain. If the tumor grows large, it may cause neurological symptoms. Usually, there’s an average five-year gap between the first symptoms and diagnosis.
- Schwannomas located in the arms or legs might not cause any symptoms, or they could cause mild pain, or a prickly or burning sensation due to nerve pressure.
- A schwannoma growing on the sciatic nerve can cause lower back pain that extends to the leg, mimicking a slipped disc.
- A schwannoma on the C7 nerve root may lead to thoracic outlet syndrome.
- A schwannoma located in the ankle or wrist could potentially result in tarsal or carpal tunnel syndrome.
- Symptoms can appear in a distant part of the body due to a tumor on a nerve close to the center of the body.
- Tumors can also affect the functioning of the body because they put pressure on the nerve where they originate.
- Vestibular schwannomas, found in the ear, typically cause hearing loss, ringing in the ear (tinnitus), and balance problems. Occasionally, a patient may also experience facial paralysis.
- Trigeminal schwannomas cause numbness or pain distributed along the trigeminal nerve. If the tumor is located at any of the nerve’s roots (V1, V2, or V3), pain and numbness occur in the corresponding area of the face.
Testing for Vestibular Schwannoma
Plain X-rays might not give clear answers in the case of a growth called an intraosseous schwannoma, which generally looks harmless. This growth can cause certain bone openings in the spine to become larger. Other potential reasons for similar symptoms could be due to chordomas, giant cell tumors, and chondroblastomas, which are different types of bone growths. These often cause bone damage, especially when they are present in the sacrum, a part of your lower back.
Seeing the inside of the body through methods such as magnetic resonance imaging (MRI) and computed tomography (CT) scans can also be considered. However, MRI is the preferred choice. MRI usually shows a round or oval mass, which is either similar in signal strength or weaker than the surrounding tissue in T1-weighted images and has a stronger, varying signal in T2-weighted images. When exposed to a substance called gadolinium contrast, the mass lights up evenly. One specific marker of a tumor related to the peripheral nerve sheath is the ‘target sign’. This presents as a region of low signal intensity surrounded by a region of high signal intensity in T2-weighted images. It’s important to note that while this sign does point towards a tumor, it’s not specifically indicative of a schwannoma.
Ultrasound is another diagnostic tool that can be utilized to detect schwannomas located just under the skin, and can also be helpful during surgery.
Treatment Options for Vestibular Schwannoma
Vestibular schwannomas, or small tumors that develop in the part of your ear that controls balance, can be managed in several ways. Tumors that are small and cause no symptoms may simply be monitored. If the tumor grows or causes symptoms, surgery or radiation therapy may be needed. However, preserving hearing can be a challenge and it often depends on the size of the tumor and the type of treatment used. To track the progress of the tumor and understand the extent of hearing loss, doctors generally recommend a hearing test and a brain scan.
Observation
Vestibular schwannomas typically grow at an average rate of about 1.4mm per year. The best approach to managing these tumors is not entirely clear due to a lack of forward-looking data. However, looking back at a large number of cases suggests that in about 65% of cases, the tumor did not grow while just observing it. In about 71% of cases, the hearing was still serviceable after two years just observing it. It’s important to note that neither surgery nor radiation can restore lost hearing and both carry the risk of causing more damage to the nerves. Watching and waiting may be the best course of action for patients with small tumors (under 1.5 cm), patients with other serious health conditions, no growth, and stable symptoms. However, patients should understand the need for regular monitoring with brain scans every six months and hearing assessments at the same time. If the tumor does not grow, these tests will be done once a year.
Patients should be aware that hearing loss can still happen during observation even if the tumor does not grow. This can happen due to the tumor putting pressure on nerves and blood vessels. A look back at previous cases showed that the percentage of patients who still had serviceable hearing after just observation dropped from 70% at diagnosis to 31% at ten years.
What else can Vestibular Schwannoma be?
The following are different types of tumors and medical conditions that could affect the nervous system:
- Meningioma
- Neurofibroma
- Malignant peripheral nerve sheath tumor
- Carcinomatous meningitis
- Plexiform neurofibroma
- Metastatic melanoma
- Malignant melanoma
- Pigmented neurofibroma
- Leiomyoma/leiomyosarcoma
- Chordomas
- Chondroblastomas
- Giant cell tumors
- Traumatic neuroma
- Pleomorphic hyalinizing angiectatic tumor
- Palisaded encapsulated neuroma
These are important medical terms doctors would use to identify and diagnose a patient’s condition.
Surgical Treatment of Vestibular Schwannoma
Surgery for vestibular schwannomas, which are benign tumors that usually grow on the nerve that connects the inner ear to your brain, results in low recurrence rates, meaning the tumor is less likely to grow back. It also has a high probability of being able to completely remove the tumor. The success of the treatment depends largely on careful patient selection and an experienced surgeon.
A large study of 1,000 vestibular schwannoma surgeries showed that complete removal of the tumor was achieved in 98% of cases, 68% of patients kept their hearing, and there was a very low risk of death (1.1%). When the entire tumor is removed, the likelihood of it growing back is at most 2%. However, if only a part of the tumor can be removed, there is approximately a 30% chance of it growing back.
Different surgical strategies may be used depending on the exact details of the patient’s condition. The retromastoid approach involves making an incision behind the ear and the mastoid bone, the bony prominence behind the ear. This approach is often able to preserve the patient’s hearing, but there’s a chance it may not remove the entire tumor. The middle cranial fossa approach makes an incision in front of the ear and could also preserve hearing, depending on tumor size. The translabyrinthine approach goes through the inner ear and will inevitably result in hearing loss, making it suitable for patients who already have severe hearing problems. Generally speaking, surgical removal is recommended for large tumors, reoccurring tumors after radiation treatment, tumors causing pressure on the brainstem, cranial nerve issues, and hydrocephalus, a condition resulting from an accumulation of fluid in the brain.
Like all surgeries, there are potential complications. These can include leakage of cerebrospinal fluid (the fluid found in and around your brain and spinal cord) after surgery (9 to 13% of cases), headaches, nerve damage (particularly to facial nerves), hearing problems, bleeding in the brain, hydrocephalus, inflammation of the brain’s lining (aseptic meningitis) occurring in 2 to 4% of patients, and muscle weakness on one side of the body (hemiparesis).
What to expect with Vestibular Schwannoma
The outlook is generally very good—recurrence or reappearance after the total removal of the tumor is rare. Although it’s infrequent, schwannomas, or nerve sheath tumors, can turn malignant or cancerous, particularly in people who already have a condition called neurofibromatosis. The prognosis or outcome can also vary depending on the size and location of the tumor and any other existing health conditions.
Recovery from Vestibular Schwannoma
People who still have usable hearing can either be observed or given a regular hearing aid. However, some patients could completely lose the ability to hear in the affected ear. If this happens, they may be suitable for hearing rehabilitation treatments. These could include bone conduction implants or a device that routes sound from the deaf ear to the good ear (this is known as “contralateral routing of signals” or CROS hearing aid). However, these treatments can only be done if a part of the inner ear called the cochlear nerve is still intact.
Facial nerve paralysis is another possible problem that may need to be managed over a long period of time. Patients may see the most improvement within the first six months. An issue that needs quick attention is incomplete eye closure as it could lead to exposure keratopathy, a condition where the outer layer of the eye gets damaged. This can be handled by placing a small weight made of gold in the upper eyelid. Other options include a surgical procedure called tarsorrhaphy and tear duct plugs. If there is only minimal improvement in six months, these patients should be referred for treatment as soon as possible.
Severe long-lasting imbalance due to the tumor itself or the treatments isn’t common but it can make a patient more likely to fall. If patients have chronic issues with balance due to problems with the inner ear, an assessment of their balance and balance therapy may be appropriate.
Preventing Vestibular Schwannoma
A schwannoma is usually not harmful, but in rare situations, it can become cancerous. It’s important for patients to regularly check in with their specialized doctors, such as a brain or nerve surgeon or a radiation oncologist, to discuss their treatment plans. Patients will likely need to have multiple CT or MRI scans to monitor the size of their tumor, especially if the doctors have decided not to immediately treat it. This is a standard procedure for tumors that are being watched closely.
