ENT · Vestibular Schwannoma
The facts most likely to be tested
Acoustic neuroma is a benign tumor arising from the vestibulocochlear nerve (CN VIII), specifically the vestibular division.
The classic clinical presentation is unilateral sensorineural hearing loss, tinnitus, and disequilibrium.
Gadolinium-enhanced MRI of the internal auditory canal is the gold standard diagnostic imaging modality.
Bilateral acoustic neuromas are pathognomonic for Neurofibromatosis type 2 (NF2), often associated with bilateral vestibular schwannomas.
Compression of the trigeminal nerve (CN V) by a large tumor results in ipsilateral facial numbness or decreased corneal reflex.
Large tumors may cause obstructive hydrocephalus due to compression of the fourth ventricle.
Management options include observation, stereotactic radiosurgery, or surgical resection depending on tumor size and patient symptoms.
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A 48-year-old male presents with a 6-month history of progressive hearing loss in his right ear and a persistent high-pitched ringing sensation. He reports occasional vertigo and a feeling of unsteadiness when walking. Physical examination reveals decreased corneal reflex on the right side and Weber test lateralizing to the left ear. Audiometry confirms unilateral sensorineural hearing loss.
What is the most appropriate next step in the management of this patient?
Gadolinium-enhanced MRI of the internal auditory canal
The patient's presentation of unilateral sensorineural hearing loss and trigeminal nerve involvement (decreased corneal reflex) is highly suggestive of an acoustic neuroma, requiring MRI for definitive diagnosis.
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High yield triage
Etiology / Epidemiology
Benign schwannoma of the vestibulocochlear nerve (CN VIII). Unilateral hearing loss in adults is the hallmark.
Clinical Manifestations
Progressive unilateral sensorineural hearing loss and tinnitus. Disequilibrium is more common than true vertigo.
Diagnosis
MRI with gadolinium contrast is the gold standard. Look for an enhancing mass in the cerebellopontine angle.
Treatment
Microsurgical resection or stereotactic radiosurgery. Facial nerve palsy is a major surgical risk.
Prognosis
Generally excellent prognosis. 95% tumor control rate with radiation.
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Epidemiology & Etiology
Acoustic neuromas, or vestibular schwannomas, are the most common tumors of the cerebellopontine angle. While usually sporadic, bilateral tumors are pathognomonic for Neurofibromatosis type 2 (NF2). They typically present in adults aged 30–60 years.
Pertinent Anatomy
The tumor arises from the vestibular division of CN VIII within the internal auditory canal. As it expands, it compresses the cochlear nerve and eventually the facial nerve (CN VII) and brainstem.
Pathophysiology
Overgrowth of neoplastic Schwann cells leads to nerve compression and demyelination. The slow-growing nature allows for central compensation, explaining why severe vertigo is rare despite vestibular involvement. Mass effect on the cerebellum or brainstem occurs only in late-stage, large tumors.
Clinical Manifestations
Patients present with insidious unilateral sensorineural hearing loss and tinnitus. Continuous disequilibrium is common, while episodic vertigo is rare. Sudden hearing loss or facial numbness (CN V involvement) suggests rapid growth or large tumor size.
Diagnosis
The MRI with gadolinium contrast is the diagnostic test of choice to identify small intracanalicular lesions. Audiometry typically reveals a high-frequency sensorineural hearing loss and poor speech discrimination scores. Avoid CT scans as they lack the sensitivity to detect small tumors in the internal auditory canal.
Treatment
Management options include observation, stereotactic radiosurgery (e.g., Gamma Knife), or microsurgical resection. Observation is reserved for small, asymptomatic tumors in elderly patients. Facial nerve injury is the most feared complication of surgical excision.
Prognosis
Most tumors are slow-growing and benign. Long-term monitoring with serial MRI is required for patients managed conservatively. Permanent sensorineural hearing loss is often irreversible even after successful tumor removal.
Differential Diagnosis
Meniere disease: episodic vertigo and fluctuating hearing loss
Labyrinthitis: acute onset of severe vertigo and hearing loss
Cholesteatoma: visible debris in the middle ear on otoscopy
Multiple Sclerosis: presence of other neurological deficits
Sudden Sensorineural Hearing Loss: rapid onset, usually viral or vascular etiology