Introduction
Vestibular schwannoma, also referred to as acoustic neuromas, are benign tumors of the Schwann cells that appear on the eighth cranial nerve. They commonly occur at the cerebellopontine angle, which is close to the facial and vestibulocochlear cranial nerves. Vestibular schwannomas remain one of the most technically challenging tumors to treat surgically at the cranial base. Over a few decades, because of technological advancements and functional outcomes, surgeons are emphasizing obtaining the best cranial nerve outcomes possible, cancer control, and posttreatment quality of life other than just saving lives. However, neurosurgical intervention plays a major option in the effective management of acoustic neurinomas.
What Is a Vestibular Schwannoma?
Vestibular schwannoma is a benign (non-cancerous), slow-growing tumor that develops from the balance and hearing nerves supplying the inner ear. The tumor occurs as a result of the overproduction of Schwann cells; these are the cells that wrap around the nerve fibers like, onion skin, to support and insulate nerves. As a result of tumor growth, the nerve balance and hearing are affected, leading to unilateral or asymmetric hearing loss, tinnitus, and dizziness or loss of balance.
The tumor can also affect the trigeminal nerve (facial sensation nerve), leading to facial numbness, and the facial nerve (affecting the facial muscles), causing facial paralysis. The large tumor can affect the brain structure by pressing against them and can be life-threatening.
What Are the Symptoms of Vestibular Schwannoma?
The symptoms include:
- Hearing loss.
- Tinnitus (a ringing sound in the ear).
- Difficulty in speech understanding.
- Ear fullness.
- Vertigo.
- Dizziness.
- Interference with cranial nerves.
- Facial numbness.
- Facial paralysis.
- Difficulty swallowing.
- Ataxia (impaired ability to coordinate with voluntary movements).
- Mental confusion.
- Headache.
- Hydrocephalus (accumulation of fluid in the skull).
How Is Vestibular Schwannoma Diagnosed?
The diagnosis is based on a thorough clinical examination, detailed patient history, identification of symptoms and clinical features, and tests such as hearing examination, MRI (magnetic resonance imaging), CT scans (computed tomography), and a specialized test to evaluate the balance (electronystagmography), and a brainstem auditory evoked response.
- Audiometry: It is a test to measure hearing functions in which the doctor asks to listen to sounds and speech while wearing earphones attached to a machine that records responses and measures the hearing function. The audiogram shows the following:
- Sound frequency.
- Speech volume- the higher the score, the lesser is hearing.
- Speech discrimination- the words to be detected; lower the score, hearing is worse.
- MRI: It is the most sensitive test for vestibular schwannomas. It is done using a contrast dye to pinpoint the tumor. In the presence of a tumor, the dye is soaked up by the tissue and gives a clear appearance of the tumor in the internal auditory canal.
What Is the Treatment for Vestibular Schwannoma?
The treatment of vestibular schwannoma includes:
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Tumor Removal: Surgical removal of tumors is highly effective for vestibular schwannomas. However, the hearing loss that has occurred due to the tumor cannot be reversed, but the hearing can be preserved in a few cases. The associated problems, such as balance or vertigo, facial numbness, dizziness, etc., can also be addressed by surgical removal.
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Stereotactic Radiosurgery: It is a common treatment used in vestibular schwannomas. This involves radiation therapy delivered precisely to the tumor with targeted radiation, avoiding the surrounding healthy tissue. Radiation therapy does not cure or remove the tumor, but it prevents further tumor growth since the vestibular schwannomas are slow-growing, and the radiation prevents the growth. Hence, it is not recommended for large tumors and for young patients.
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Observation: In cases with small tumors, observation therapy is followed, which means waiting and watching. As these tumors are slow-growing, immediate treatment intervention may not be required as the earlier stages do not present with any symptoms. MRI is advised for patients with other medical conditions to monitor the tumor size and progression, followed by a treatment plan.
What Are the Surgical Approaches to Treat Vestibular Schwannoma?
Surgical approaches include:
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Middle Cranial Fossa: This is the approach to preserve hearing and is applicable to patients with good hearing and small tumors that are located primarily within the internal auditory canal. The advantage is to preserve hearing, and the disadvantage is the need for temporal lobe retraction, which can produce seizures and venous infarction if the vein of the Labbe is damaged.
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Retrosigmoid Approach: This technique can be used for small to moderate tumors that are growing beyond the internal auditory canal. This is a workhouse approach in skull base surgery and provides good access to the cranial nerves located at the skull base. Through this approach, tumors of any size can be accessed while preserving hearing, although large tumors have decreased chances of hearing preservation.
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Translabyrinthine Approach: This approach can be used for tumors of any size that has caused significant hearing loss or in cases where hearing preservation is impossible because of tumor size. The procedure includes the removal of bone behind the ear to access the tumor through the inner ear. It also provides access to the facial nerve and requires less retraction of the brain. It cannot preserve hearing but can improve the outcomes such as facial nerve preservation, survival rate, and interference with other cranial nerves.
The goal of treatment is to preserve hearing, facial nerve function, and other nerves with improved outcomes and maintain the quality of life.
What Are the Complications Associated With Vestibular Schwannoma Surgery?
Complications include:
- Hearing loss.
- Facial weakness or numbness.
- Headache.
- Decreased mental alertness.
- Obstruction of cerebrospinal fluid.
- Meningitis.
- Facial never damage.
- Facial paralysis.
Conclusion
Vestibular schwannomas are benign and uncommon tumors. They present with unilateral or bilateral hearing loss followed by dizziness, balance issues, vertigo, tinnitus, etc. It is caused by the overgrowth of Schwann cells around the cranial nerve and can interfere with nerve functioning. The diagnosis is made based on hearing tests and MRIs. Treatment includes surgical approaches and stereotactic radiotherapy. In case of small tumors with no symptoms, the patient is kept on observation.
