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Misdiagnosed Brain Tumors: Acoustic Neuroma
Acoustic neuroma, also known as vestibular schwannoma or schwannoma of the auditory nerve, is a type of schwannoma that develops along the eighth cranial nerve. Acoustic neuromas account for about 8% of all intracranial tumors. Regionally, these tumors are commonly found in the cerebellopontine angle, constituting approximately 80 to 90% of all tumors in this area.
The auditory and vestibular nerves connect the inner ear to the brainstem. Acoustic neuromas are benign tumors that grow slowly, typically increasing by 1 to 2 millimeters per year. In general, 90% of these tumors are unilateral, affecting either the left or right side, with an equal chance of occurring on either side. About 10% of cases are bilateral, appearing simultaneously or at different times on both sides. Acoustic neuromas are often perceived as severe because they reside within the brain; however, they typically present with mild and slow onset of symptoms such as tinnitus, which are easily misdiagnosed or missed.
As the tumor enlarges, it can lead to facial muscle paralysis due to compression of the cranial nerves, potentially affecting the fifth, seventh, and eighth nerves.
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Symptoms associated with the auditory and vestibular nerves include hearing loss and tinnitus in 95% of patients, with vertigo being less common (61%).
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Trigeminal nerve: 17% of patients may experience facial numbness, heightened sensitivity to facial sensations, or pain.
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Facial nerve: About 6% of patients might experience facial muscle weakness or abnormal taste sensations.
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Other symptoms: When the tumor compresses the ninth, tenth, and eleventh cranial nerves, patients may suffer from swallowing difficulties and speech problems. Larger tumors pressing on the cerebellum or brainstem can lead to muscle weakness, postural and balance disorders, and unstable gait, with severe cases risking hydrocephalus or even death.
Magnetic Resonance Imaging Diagnosis
Magnetic resonance imaging (MRI) helps in accurately diagnosing and differentiating tumors in the cerebellopontine angle region, such as meningiomas, epidermoid cysts, and trigeminal schwannomas.
Characteristics of acoustic neuroma on MRI:
The tumor can be seen extending from the internal auditory canal towards the inside, resembling the tail of a tadpole.
The tumor's pressure on the cerebellum and brainstem.
Consideration of minimally invasive microsurgical removal for larger tumors or those compressing significant nerves.
Neurosurgeons will evaluate various factors to formulate an appropriate treatment plan. If the tumor is small and asymptomatic, the patient may undergo conservative treatment with regular follow-ups and checks. If the tumor is large or compresses significant nerves, causing symptoms and significant effects, minimally invasive microsurgery may be considered.
Minimally Invasive Microsurgical Surgery for Protecting Auditory and Facial Nerves
Typically, microsurgical removal is a definitive treatment for acoustic neuromas. However, due to the close relationship between the tumor, nerves, and brainstem, the surgery carries certain risks, particularly damage to the auditory nerve leading to hearing loss or to the facial nerve causing facial paralysis. However, experienced neurosurgeons perform these surgeries under a microscope with delicate precision and continuous intraoperative neural monitoring (IOM), significantly enhancing the preservation of auditory and facial nerve functions. Experienced neurosurgeons achieve a total removal rate of 97 to 100%, with a facial nerve function preservation rate of 51 to 98.2%, and a hearing preservation rate of 19 to 40%. The recurrence rate for these tumors is between 5 to 10%.
Radiosurgery with CyberKnife
CyberKnife radiosurgery is suitable for tumors less than 3 cm in size or for residual tumors post-surgery. It is also appropriate for elderly patients or those in poor health. CyberKnife offers a relatively low risk, quick recovery, and short treatment duration, typically between 3 to 7 days. The effectiveness of the treatment correlates with the radiation dose, although it is not recommended for tumors with cystic changes or significant brainstem compression. The principle behind the treatment involves high-energy radiation to kill tumor cells or control their growth. In the short term post-treatment, tumors may swell and enlarge, hence, dehydration treatments to reduce cranial pressure may be necessary shortly after the procedure. Medical literature indicates that CyberKnife treatment for acoustic neuromas has a tumor control rate of 85 to 100%, a hearing preservation rate of 60%, and a complication rate of 5.6%.
Conclusion
Once an acoustic neuroma is diagnosed, if the tumor is large or compresses important nerves, causing significant symptoms and impact, treatment should be pursued promptly to completely eradicate the tumor while preserving auditory and facial nerve functions. For older patients with poor health, small tumors, no brainstem compression, or residual tumors post-surgery, conservative treatment with regular follow-ups or CyberKnife radiosurgery may be used to control tumor growth. The specific treatment plan should be developed by experienced neurosurgeons after a comprehensive assessment and in conjunction with the patient and family's wishes.
Middle-aged individuals experiencing tinnitus and hearing loss should not ignore these symptoms, as they could be early signs of an acoustic neuroma. Early detection and diagnosis can significantly improve treatment outcomes and the preservation of auditory and facial nerve functions.