Acoustic Neuroma Explained: Symptoms, Diagnosis, and Treatments
What is Acoustic Neuroma?
Acoustic neuroma, also known as vestibular schwannoma, represents an uncommon cause of hearing loss. It's a noncancerous (benign) tumor that develops on the main nerve leading from the inner ear to the brain, namely, the eighth cranial nerve. This nerve, also called the vestibulocochlear nerve, comprises two parts: the cochlear and the vestibular nerve. Each part performs a different role in hearing; one transmits sound while the other conveys balance information.
The growth of an acoustic neuroma can disrupt balance and hearing, causing:
- Loss of hearing
- Unsteadiness
- Ringing in the ear (tinnitus)
Acoustic neuroma usually develops very slowly; however, there are a few exceptions. In rare cases, the tumor can grow rapidly, pressing on adjacent cranial nerves. Several studies suggest that this abnormal tumor growth can be lethal if it becomes big enough to press on the cerebellum or brainstem.
KEY POINTS
- Acoustic Neuroma is a benign tumor affecting the vestibulocochlear nerve, crucial for hearing and balance.
- Prevalence and Incidence: Recent studies indicate that Acoustic Neuromas have an incidence rate of approximately 20 per million people per year (1).
- Symptoms often start subtly, with one-sided hearing loss, tinnitus, and balance problems being common.
- Diagnosis primarily relies on MRI imaging and hearing tests, with balance and auditory tests providing further insights.
- Mortality Rate: Advances in surgical techniques and postoperative care have significantly reduced mortality rates associated with Acoustic Neuroma. The mortality rate following surgery is typically less than 0.5% (2, 3).
- Progression-Free Survival (PFS): Recurrence-free survival rates after surgical resection or radiosurgery are notably high, with studies reporting PFS rates of 97% at 5 years for patients undergoing stereotactic radiosurgery (4).
- Functional Outcome and Quality of Life: Surgical intervention and radiosurgery have evolved to prioritize not only the control of tumor growth but also the preservation of neurological function, aiming to maintain the patient's quality of life (2).
Symptoms of Acoustic Neuroma
Acoustic neuromas usually grow slowly, about 1-2 mm yearly, often without early symptoms. Most patients often fail to identify any symptoms in the initial stage and often consider them as normal changes due to aging. Research shows these tumors don't always grow steadily; sometimes, they stop growing for extended periods. This can delay symptom identification and diagnosis.
Typically, the first sign is gradual hearing loss in one ear, often with tinnitus (ear ringing) and a sensation of ear fullness.
Early Stages
- Often asymptomatic
- May cause slow hearing loss, tinnitus, and ear pressure
Usual Symptoms
- Hearing loss
- Equilibrium issues
- Tinnitus
- Vertigo
- Unsteadiness
Relatively Rare Symptoms
- Facial numbness or pain
- Temporary vision loss
- Taste changes
- Difficulty swallowing
- Headache
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Diagnosis of Acoustic Neuroma
Diagnosing acoustic neuroma involves a combination of patient history evaluation, symptom assessment, and specialized tests. The goal is to accurately identify the presence and assess the size and impact of the tumor on surrounding structures.
Initial Evaluation
The process typically begins with a detailed discussion of symptoms such as hearing loss, tinnitus, and balance issues. A physical examination, focusing on neurological health, helps in identifying any nerve-related abnormalities.
Hearing Tests (Audiometry)
Audiometry is a primary diagnostic tool for acoustic neuroma. This test measures hearing sensitivity in each ear, identifying hearing loss patterns characteristic of an acoustic neuroma.
Imaging Tests
- Magnetic Resonance Imaging (MRI): The most definitive test for detecting acoustic neuromas. MRI uses magnetic fields and radio waves to produce detailed images of the brain and inner ear, revealing the presence and size of the tumor.
- Computed Tomography (CT) Scan: Sometimes used when MRI is unavailable or contraindicated. CT scans can show the tumor's location and effects on surrounding bone, though they are less sensitive than MRIs for this condition.
Balance Tests
Balance or vestibular testing may be performed to evaluate the vestibular system's function, which can be affected by an acoustic neuroma. Tests like the Videonystagmography (VNG) or Electronystagmography (ENG) assess balance and coordination.
Advanced Auditory Tests
Tests such as Auditory Brainstem Response (ABR) or Brainstem Auditory Evoked Responses (BAER) measure the brain's electrical response to sound. These can detect abnormalities in the auditory pathway caused by the tumor.
Acoustic Neuroma Treatments
There are three main treatment options for acoustic neuroma, depending on tumor size, location, patient age, and health:
- Monitoring or Observation
- Surgery
- Radiotherapy
Monitoring
Given the tumor's slow growth, monitoring with regular MRI scans is often advised for small tumors. This approach avoids the risks associated with surgery and radiotherapy, such as hearing loss and facial nerve damage. Treatment adjustments are made based on tumor growth and symptom development.
Surgery
Microsurgery involves removing all or part of the tumor under general anesthesia through skull incisions. There are three surgical approaches:
- Translabyrinthine: Involves an ear-behind incision, removing some inner ear bone. This approach usually results in hearing loss in the affected ear but tends to preserve facial nerve function.
- Retrosigmoid: Opens a portion of the skull near the ear to remove large tumors while attempting to preserve hearing.
- Middle Fossa: Targets tumors in the internal auditory canal with a focus on preserving hearing, though it risks facial nerve damage and requires specialized surgical skills.
Radiotherapy
Used mainly for small tumors or remaining tumor parts post-surgery, radiotherapy delivers targeted radiation doses under local anesthesia, either in one session or multiple smaller doses. This method aims to slow or stop tumor growth without harming surrounding tissues. It's not suitable for large tumors.
Final Thoughts
Acoustic Neuroma, though rare, poses significant challenges due to its impact on hearing and balance. Recent advancements in diagnosis and treatment have improved patient outcomes, emphasizing the importance of early detection and personalized care strategies. With a high progression-free survival rate following treatment, the focus remains on minimizing side effects and preserving quality of life.
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Medical References
- Brun L, Mom T, Guillemin F, Puechmaille M. The Recent Management of Vestibular Schwannoma Radiotherapy: A Narrative Review of the Literature. Journal of Clinical Medicine. 2024.
- Gawish A, Walke M, Röllich B, Ochel HJ, Brunner TB. Vestibular schwannoma hypofractionated stereotactic radiation therapy in five fractions. Clinical Oncology. 2023.
- McClelland III S, Kim E, Murphy JD, Jaboin JJ. Operative mortality rates of acoustic neuroma surgery: a national cancer database analysis. Otology & Neurotology. 2017 Jun 1;38(5):751-3.
- Wach J, Güresir Á, Borger V, Schuss P, Becker A. Elevated baseline C-reactive protein levels predict poor progression-free survival in sporadic vestibular schwannoma. Journal of Neuro-Oncology. 2022.
- Brachimi E, Sooby P, MAM Slim, et al. The impact of multiple deprivation on the management of vestibular schwannomas. European Archives of Oto-Rhino-Laryngology. 2024.
- You N, Zhang J, Zhang D, Zhao Y, Zhang J, et al. Predictive factors of tinnitus after vestibular schwannoma surgery: a case-control study. Chinese Neurosurgical Journal. 2024.
- Patra A, Deswal MM, Navreet M, Sarin M, Yadav S, et al. Role of High-Resolution Computed Tomography to Evaluate the Abnormalities of Temporal Bone - Systematic Review Study. ResearchGate. 2024.
- Tunkel AE, Youner ER, Barseghyan H, et al. Four distinct ipsilateral vestibular schwannomas: A case of mosaic NF2-related schwannomatosis. American Journal of Clinical Pathology. 2024.
- Irfan S, Kadam AD, Ravichandran U. An Atypical Presentation of Acoustic Neuroma With Facial Paresthesia: A Case Report. Cureus. 2024.
- Scheich M, Bürklein M, Stöth M, Bison B, Hagen R, et al. A Retrospective Analysis of Temporal Lobe Gliosis after Middle Fossa Resection of Small Vestibular Schwannomas. Brain Sciences. 2024.
