ENT · Vestibular Schwannoma
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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 loss of corneal reflex.
Large tumors may cause obstructive hydrocephalus or brainstem compression due to their location in the cerebellopontine angle.
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 to the clinic complaining of a 6-month history of progressive hearing loss in his right ear and a constant high-pitched ringing sensation. He reports occasional episodes of mild imbalance when walking. Physical examination reveals decreased right-sided corneal reflex and diminished right-sided facial sensation. Weber test lateralizes to the left ear, and Rinne test is positive bilaterally.
What is the most appropriate next step in the diagnostic evaluation of this patient?
Gadolinium-enhanced MRI of the internal auditory canal
The patient's presentation of unilateral sensorineural hearing loss and trigeminal nerve involvement (loss of corneal reflex) is highly suggestive of a cerebellopontine angle tumor, requiring MRI for definitive diagnosis.
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Etiology / Epidemiology
Benign schwannoma of the vestibulocochlear nerve (CN VIII). Unilateral hearing loss in an adult is the classic presentation.
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 radiotherapy. Facial nerve palsy is a major surgical risk.
Prognosis
Generally excellent outcomes. 95% tumor control rate with radiation; monitor for hearing preservation.
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Epidemiology & Etiology
Acoustic neuromas, or vestibular schwannomas, typically arise in the 4th to 6th decades of life. While most are sporadic, bilateral tumors are pathognomonic for Neurofibromatosis type 2 (NF2). They originate from the myelin-forming cells of the vestibular division of the CN VIII.
Pertinent Anatomy
The tumor typically originates within the internal auditory canal. As it expands, it enters the cerebellopontine angle, where it can compress the trigeminal nerve (CN V) and the facial nerve (CN VII).
Pathophysiology
Slow-growing, benign tumors cause symptoms via mass effect and compression of adjacent structures. Compression of the cochlear nerve leads to hearing loss, while vestibular nerve involvement causes imbalance. Late-stage growth can lead to obstructive hydrocephalus due to compression of the fourth ventricle.
Clinical Manifestations
Patients present with insidious unilateral sensorineural hearing loss and tinnitus. A key board finding is decreased corneal reflex due to compression of the CN V sensory fibers. Sudden onset of severe headache or ataxia suggests significant brainstem compression or hydrocephalus.
Diagnosis
The MRI with gadolinium contrast is the diagnostic test of choice to identify small intracanalicular lesions. Audiometry is the initial screening tool, typically showing a high-frequency sensorineural hearing loss and poor speech discrimination.
Treatment
Management options include observation (serial MRI), stereotactic radiotherapy, or microsurgical resection. Facial nerve injury is the most feared complication of surgical excision. Observation is often reserved for elderly patients or those with small, asymptomatic tumors.
Prognosis
Long-term prognosis is excellent for tumor control. Hearing preservation is the primary goal but is difficult to achieve in large tumors. Patients require long-term serial MRI monitoring to ensure no recurrence or growth.
Differential Diagnosis
Meniere disease: episodic vertigo and fluctuating hearing loss
Cholesteatoma: chronic ear drainage and conductive hearing loss
Labyrinthitis: acute onset of continuous vertigo and hearing loss
Multiple Sclerosis: bilateral symptoms and other CNS deficits
Meningioma: broad-based dural attachment on MRI