Medical symptom checker - Tinnitus - Acoustic neuroma symptoms
Medical symptom checker- tinnitus - benign acoustic neuroma
What is benign acoustic neuroma?
Acoustic neuroma is a benign schwannoma ( slow growing benign tumor). It arises from the vestibular division of the 8th cranial nerves sheath. Acoustic neuroma is originated from Schwann cells of the nerve sheath and arises from the internal auditory canal close to the cerebellopontine angle.Acoustic neuroma is mostly unilateral and bilaterally cases of acoustic neuroma is associated with neurofibromatosis type 2.
What is the causes and pathology behind acoustic neuroma ?
The benign schwannoma ( acoustic neuroma ) originating form the perineural element of the vestibular nerve and rarely arise from cochlear portion of the 8th cranial nerve . The benign schwannoma then expend from the internal auditory canal onto the cerebellopontine angle and causes compression of the surrounding structure such as cranial nerves ( facial nerve and cranial nerve as well as trigeminal nerve ) and brainstem and 4th ventricle in the surrounding region.
What are the associated risk factor for acoustic neuroma?
Acoustic neuroma is associated with pregnancy and seizures. Pregnancy may accelerates the growth of the tumor. Bilateral acoustic neuroma is associated with neurofibromatosis type 2. Neurofibromatosis type 2 is an autosomal dominant condition that affect the genes located on the chromosome 22q1. Besides bilateral acoustic neuroma, patient with neurofibromatosis type 2 may also present with gliomas, meningiomas, and spinal as well as peripheral schwannoma and present before 30 years of age. Acoustic trauma such as exposure to loud noise may also be associated with acoustic neuroma.
How common is acoustic neuroma ?
95% of acoustic neuroma cases are unilateral. Acoustic neuroma is 10% of all intracranial tumor. Acoustic neuroma is 80% -90% of all cerebellopontine angle tumor.
Occurs at any age, but most commonly present in 40 -50 years ( unilateral acoustic neuroma ) and 20 -30 years ( bilateral acoustic neuroma ) . The incidence of acoustic neuroma is 1/ 100000 per year with asymptomatic lesion is more common. In US the prevalence is around 3000 cases diagnosed annually.
What are the signs and symptoms of acoustic neuroma ?
Commonly the patient may present with unilateral sensorineural hearing loss, tinnitus, loss of balance and and vertigo.
Less common for the patient to suffer from hydrocephalus and headache as well as increase in intracranial pressure or loss of facial muscle function or weakness .Patient also is rarely to suffer from ataxia due to cerebellar or brainstem involvement.
Trigeminal nerve compression may also happen due to very large tumor.Patient may also complains of progressive hearing loss and the loss of speech discrimination.
On examination the patient may present with progressive unilateral sensorineural hearing loss Patient develop nystagmus to the sides opposites to the tumors. Examination with otoscope is require to exclude other causes such as wax, infection, middle ear effusion, tympanic membrane rupture and cholesteatoma. Cranial nerves investigations in details are important.Large tumor may compress trigeminal nerve and leads to loss of corneal reflex and unilateral facial numbness. Compression of facial nerve may leads to lower motor neuron facial palsy. Rinne and Weber test are important in evaluation and confirming the sensorineural hearing loss.
Patient < 30 years old , should be evaluated for contralateral ear if suspects of neurofibromatosis type 2. Brainstem - cerebellar compartment may present with ipsilateral ataxia, reversal of the nystagmus and bulbar cranial nerve palsies. Obstruction at the level of 4th ventricles may present with occipital headache, increase in intracranial pressure and hydrocephalus.
How to investigates acoustic neuroma ?
Speech as well as pure tone audiometry may produce high frequency asymmetrical sensorineural hearing loss.
Stacked auditory brainstem response (ABR) able to detect tumor less than 1cm with sensitivity around 95% and specificity around 88% .
Standard auditory brainstem response ( SABR) able to detect tumor > 1cm.
Auditory evoked potential will show a waveform delay and excluding a lesion in the cochlear
MRI with gadolinium enhancement is able to highlight the tumor clearly. The specificity is 100%. It able to detect tumor from 2 mm in sizes.
Other alternative to MRI with gadolinium enhancement is non - contrast T2 weighted fast spin echo- MRI which is cheaper with specificity around 98%
CT scan is other imaging technique that able to detect tumor as small as 1 cm and provides relevant information regarding bony structure surrounding the tumor. However it provides 37% of false negative result.
What is the pathophysiology of acoustic neuroma ?
Acoustic neuroma is presented with well demarcated encapsulated dense or cystic mass with neural attachment without direct invasion.
Microscopically it represent a zones alternatively dense and spares cellular component or Antoni A or Antoni B
Other disorder that may mimic acoustic neuroma may includes- cerebellopontine lesions such as facial nerve schwannoma , arachnoid cysts, meningioma , epidermoid and glioma.
Other diagnosis include ototoxicity, cerebellar pathology, Meniere disease and presbycusis .
Ho to manage acoustic neuroma ?
No medical treatment is required.
Conservative treatment / management is given to patient who is elderly, contraindicated to radiotherapy and surgery , and tumor growth rate < 2mm per year
It may include stereotactic radio surgery which is performed if tumor < 3 cm or contraindicated to microsurgery.
The tumor control range between 86% - 100% ( < 2mm growth per year ). Lower dose radiation carries less complication than high dose radiation in controlling tumor growth.
The complication may includes facial and trigeminal neuropathy .
Fractioned stereotactic radio surgery is another alternative which provides less damage to the surrounding healthy tissue by delivering higher dose radiation ( conformal radiation ) . Multiple treatment is required.
Surgical approaches may include middle fossa , translabyrinthine and suboccipital approach . It is a curative treatment, however permanent hearing impairment is unavoidable, In this case before undergoes any curative surgery , patient is advised to learn how to use sign languages and lip reading.
Endoscopic procedure can also be performed to remove the tumor.
What are the complications of acoustic neuroma ?
The complication of acoustic neuroma may includes hydrocephalus, cranial nerve compression, brainstem compression, cerebellar compression, pyramidal tract compression and the 4th ventricles compression. Other complications may includes, hearing loss, headache, meningitis, facial nerve injury and CSF leakage.
What is the prognosis of acoustic neuroma ?
In term of prognosis, hearing loss appear to be permanent and treatment merely prevent further damaged.
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