Acoustic neuroma

Acoustic Neuroma (Vestibular Schwannoma)

Acoustic neuroma, also known as vestibular schwannoma, is a benign tumor originating from the Schwann cells of the vestibulocochlear nerve (cranial nerve VIII). It primarily affects the vestibular component of the nerve and is slow-growing, but its location within the cerebellopontine angle can lead to significant clinical implications due to compression of adjacent structures.

Epidemiology

• Rare, with an annual incidence of approximately 1 per 100,000 people.
• Most common in adults aged 30–60 years.
• Sporadic in most cases; about 5% are associated with neurofibromatosis type 2 (NF2).

Pathophysiology

• Originates from Schwann cells, typically at the junction of the vestibular nerve and the internal auditory canal.
• Progressive growth can lead to compression of adjacent structures, including the cochlear nerve, facial nerve, and eventually the brainstem and cerebellum.

Clinical Features

1. Auditory Symptoms:
   • Unilateral sensorineural hearing loss (most common presenting symptom).
   • Tinnitus in the affected ear.
2. Vestibular Symptoms:
   • Imbalance or unsteadiness.
   • Vertigo is uncommon because of the slow tumor growth allowing for vestibular compensation.
3. Facial and Trigeminal Nerve Involvement:
   • Facial numbness or weakness (compression of cranial nerve V or VII).
   • Facial muscle twitching or hypoesthesia.
4. Advanced Symptoms:
   • Signs of brainstem compression: ataxia, dysarthria.
   • Increased intracranial pressure: headache, nausea, papilledema.

Differential Diagnosis

• Meniere’s disease.
• Sudden sensorineural hearing loss.
• Other cerebellopontine angle tumors (e.g., meningioma, epidermoid cyst).
• Multiple sclerosis (if presenting with hearing or balance issues).

Investigations

1. Audiometry:
   • Unilateral sensorineural hearing loss.
2. Magnetic Resonance Imaging (MRI):
   • Gold standard for diagnosis.
   • T1-weighted MRI with gadolinium shows enhancement of the tumor.
3. CT Scan:
   • Useful for detecting bone involvement but less sensitive for soft tissue tumors.
4. Vestibular Testing:
   • May show reduced or absent caloric response on the affected side.
5. Brainstem Auditory Evoked Potentials (BAEP):
   • May reveal delayed conduction in the auditory nerve pathways.

Management

1. Conservative Management:
   • Observation with serial MRI in asymptomatic or minimally symptomatic patients, particularly in elderly individuals or slow-growing tumors.
2. Surgical Management:
   • Indicated for large or symptomatic tumors causing mass effect.
   • Approaches: translabyrinthine, retrosigmoid, or middle fossa craniotomy, depending on tumor size and location.
3. Radiation Therapy:
   • Stereotactic radiosurgery (e.g., Gamma Knife): effective for small-to-medium-sized tumors, aiming to arrest growth.
4. Supportive Management:
   • Hearing aids for hearing loss.
   • Vestibular rehabilitation for balance issues.

Complications

• Post-surgical complications: hearing loss, facial nerve palsy, cerebrospinal fluid leak.
• Long-term: persistent imbalance, tinnitus, or hydrocephalus.

Prognosis

• Generally excellent for small tumors if detected early.
• Large tumors may cause life-threatening brainstem compression if untreated.
• Advances in microsurgical techniques and radiosurgery have significantly improved outcomes and reduced morbidity.

Key Points for GP Exams

• Always suspect acoustic neuroma in patients with unilateral sensorineural hearing loss or persistent unilateral tinnitus.
• Early referral to ENT or a neurologist is critical for timely diagnosis and management.
• Emphasize multidisciplinary care involving audiologists, neurosurgeons, and radiation oncologists.
• For neurofibromatosis type 2 patients, consider screening for bilateral acoustic neuromas.