Makindo Medical Notes

Acoustic neuroma, also known as vestibular schwannoma, is a benign tumour arising from the Schwann cells of the vestibulocochlear nerve (cranial nerve VIII). It is a recognized cause of raised cerebrospinal fluid (CSF) protein levels and can lead to significant neurological complications if left untreated.

Encased nerve from ear
Muffled sound, can barely hear
Bone cored from within
MRI, ice cream cone seen
Two points to familiar gene
@DrCindyCooper

About

• A benign schwannoma of the vestibulocochlear nerve (cranial nerve VIII).
• Accounts for approximately 8% of all primary intracranial tumours and 80% of tumours in the cerebellopontine angle.
• Can be bilateral in neurofibromatosis type 2 (NF2) due to mutations in the NF2 gene encoding the protein merlin.
• Typically slow-growing but can cause significant morbidity due to compression of adjacent neural structures.

Aetiology

• Originates from Schwann cells responsible for myelination of peripheral nerves.
• Occurs sporadically or as part of genetic conditions like NF2.
• Exact cause is often unknown but involves genetic mutations leading to uncontrolled cell growth.

Risk Factors

• Increasing age—most commonly diagnosed between 40 and 60 years.
• Genetic predisposition—NF2 is inherited in an autosomal dominant pattern.
• Exposure to prolonged high-dose radiation, particularly during childhood.
• No definitive link established with environmental or occupational exposures.

Effects of Tumor Expansion

• Compression of Cranial Nerve VIII: Leads to unilateral sensorineural hearing loss, tinnitus, and balance disturbances.
• Compression of Cranial Nerve V (Trigeminal): Causes facial numbness, paresthesia, and reduced corneal reflex.
• Compression of Cranial Nerve VII (Facial): Results in facial weakness or lower motor neuron facial palsy.
• Cerebellar Compression: Leads to ipsilateral cerebellar ataxia and coordination difficulties.
• Brainstem Compression: May cause life-threatening conditions like hydrocephalus due to obstruction of cerebrospinal fluid pathways.
• Hydrocephalus: Obstruction of the fourth ventricle can increase intracranial pressure, leading to headaches, nausea, and vomiting.

Clinical Features

• Hearing Loss: Unilateral sensorineural hearing loss is the most common initial symptom.
• Tinnitus: Ringing or buzzing noise in the affected ear.
• Vertigo and Balance Issues: Due to vestibular nerve involvement.
• Facial Numbness: From trigeminal nerve compression.
• Facial Weakness: Resulting from facial nerve compression.
• Headaches: May indicate increased intracranial pressure.
• Ataxia: Unsteady gait and coordination problems due to cerebellar involvement.
• Possible signs of neurofibromatosis type 2 if bilateral tumours are present.

Investigations

• Audiometry: Assesses the extent of hearing loss.
• Magnetic Resonance Imaging (MRI): The gold standard for diagnosis. MRI with gadolinium contrast enhances tumour visualization, revealing the characteristic "ice cream cone" appearance at the internal acoustic meatus.
• Computed Tomography (CT) Scan: Used when MRI is contraindicated; less sensitive but can detect larger tumours and bony erosion.
• Brainstem Auditory Evoked Potentials (BAEP): Evaluates the integrity of the auditory pathway.
• Cerebrospinal Fluid (CSF) Analysis: May show elevated protein levels but is nonspecific.
• Genetic Testing: Considered if NF2 is suspected, especially in younger patients or those with bilateral tumours.

Differential Diagnosis

• Meningioma: Especially those occurring at the cerebellopontine angle.
• Epidermoid Cysts: Benign lesions that can mimic symptoms.
• Other Schwannomas: Involving different cranial nerves.
• Metastatic Tumors: Secondary tumours that have spread to the brain.
• Multiple Sclerosis: Can present with similar neurological symptoms.

Management

• Observation: Small, asymptomatic tumours may be monitored with regular MRI scans.
• Microsurgical Excision: The treatment of choice for symptomatic or growing tumours. Techniques include the translabyrinthine, retrosigmoid, or middle fossa approaches.
• Stereotactic Radiosurgery: Options like Gamma Knife or CyberKnife are less invasive and used for small to medium-sized tumours or in patients who are poor surgical candidates.
• Radiotherapy: Fractionated radiotherapy may be considered in certain cases.
• Rehabilitation: Audiological support, vestibular therapy, and facial nerve rehabilitation as needed.
• Multidisciplinary Approach: Involvement of neurosurgeons, otolaryngologists, radiologists, and audiologists.

Prognosis

• Generally good with appropriate treatment.
• Hearing preservation depends on tumour size and treatment modality.
• Risk of recurrence exists, necessitating long-term follow-up.
• Early detection improves outcomes and reduces complications.

Prevention and Screening

• No established preventive measures for sporadic cases.
• Genetic counseling and regular screening MRIs for individuals with NF2.

References

• NHS: Acoustic Neuroma
• Radiopaedia: Vestibular Schwannoma
• Vestibular Schwannoma: An Overview