Vestibular Schwannoma – 7 Interesting Facts

Interesting Facts

  1. Vestibular schwannoma is a rare, benign tumor originating from Schwann cells in the vestibular portion of the eighth cranial nerve in the inner ear
  2. Majority of these tumors are unilateral; bilateral tumors typically occur in association with neurofibromatosis type 2
  3. Hearing loss is the most common presenting symptom; other symptoms include tinnitus; vertigo; and facial numbness, weakness, or paralysis on ipsilateral side of tumor, if tumor is large
  4. Diagnosis is based on history, audiometric testing, and MRI of brain and internal auditory canal
  5. Treatment recommendations vary according to tumor size, hearing status, comorbidities, and patient preference. Options include observation, microsurgical resection, and stereotactic radiosurgery or radiotherapy
  6. Majority of small to medium tumors can be controlled by all treatment modalities
  7. Permanent hearing loss is the most frequent serious complication; tinnitus, balance disturbances, facial weakness, and headaches also occur

Pitfalls

  • Presenting symptoms may be misattributed to another condition resulting in complications due to lack of timely diagnosis

Urgent Action

  • Large tumors (more than 3 cm in diameter 1 2) associated with brainstem and/or cerebellar compression require urgent microsurgical treatment
    • Death may occur if untreated

Terminology

Clinical Clarification

  • Vestibular schwannoma is a rare, benign tumor originating from Schwann cells in the vestibular portion of the eighth cranial nerve in the inner ear 2 4
    • Formerly known as acoustic neuroma

Classification

  • Unilateral (77%-95% 42
    • Usually sporadic
    • Accounts for 80% of all tumors in cerebellopontine angle 5
  • Bilateral 2 4
    • Majority are inherited; usually occur in association with neurofibromatosis 2 6
    • Associated with tumors affecting other nerves, the brain, or the spinal cord 7

Diagnosis

Clinical Presentation

  • From Pamias-Portalatín EF et al: Vestibular schwannomas. In: Quiñones-Hinojosa A, ed: Video Atlas of Neurosurgery. Elsevier; 2017:254-66, Figure 37.1.The 4 stages of growth of vestibular schwannomas according to their extension. – (A) Stage I: intracanalicular; (B) Stage II: cisternal; (C) Stage III: brainstem compressive; (D) Stage IV: hydrocephalic.
  • From Pamias-Portalatín EF et al: Vestibular schwannomas. In: Quiñones-Hinojosa A, ed: Video Atlas of Neurosurgery. Elsevier; 2017:254-66, Figure 37.3.The usual anatomic landmarks for the 3 surgical approaches to acoustic neuroma. – (A-D) Retrosigmoid/suboccipital, translabyrinthine, and middle fossa.

History

  • Symptom onset is gradual and typically includes: 2 4
    • Hearing loss
    • Tinnitus
      • Tinnitus grading system for vestibular schwannomas.GradeDescriptionsINo tinnitusIIIntermittent or mild tinnitus, can only be heard when the ambient noise is lowIIIPersistent or moderate tinnitus, can be heard every dayIVPersistent and severe tinnitus, interfere with work and sleep View full sizeCitation: From Wu H et al: Summary and consensus in 7th International Conference on acoustic neuroma: an update for the management of sporadic acoustic neuromas. World J Otorhinolaryngol Head Neck Surg. 24;2(4):234-9, 2016, Table 1.
    • Dizziness or vertigo
      • Dizziness grading system for vestibular schwannomas.GradeDescriptionsINo dizziness or imbalanceIIOccasional and mild dizziness or imbalanceIIIPersistent or moderate vertigo or imbalanceIVPersistent and severe dizziness or imbalance, disturbing daily life View full sizeCitation: From Wu H et al: Summary and consensus in 7th International Conference on acoustic neuroma: an update for the management of sporadic acoustic neuromas. World J Otorhinolaryngol Head Neck Surg. 24;2(4):234-9, 2016, Table 2.
    • Facial numbness, weakness, or paralysis on ipsilateral side of tumor, if tumor is large
  • Unilateral vestibular schwannoma causes symptoms on side of affected ear 8
  • Bilateral vestibular schwannomas cause symptoms in both ears. Typical onset occurs in adolescence or early adulthood 9

Physical examination

  • Often no abnormal physical signs are present at time of diagnosis. Otoscopic examination is unremarkable 8 10
  • Presence of Hitzelberger sign (increased sensitivity of posterior auditory canal to light touch) suggests possible vestibular schwannoma 11
  • Hearing impairment may be evident when assessed by whispered voice or tuning fork testing
    • Weber and Rinne tests typically reveal sensorineural hearing loss
  • Cranial nerve examination commonly reveals additional deficits 2
    • Decreased or absent corneal reflex
    • Facial nerve weakness, decreased sensation, and asymmetry may be present with large tumors
  • Rare findings, including facial drooping and gait ataxia, may be observed with large tumors that are causing brainstem mass effect and obstructive hydrocephalus

Causes and Risk Factors

Causes

  • Tumor is caused by abnormal growth and proliferation of Schwann cells originating from glial-Schwann cell junction 12

Risk factors and/or associations

Age
  • Unilateral vestibular schwannoma typically presents in patients aged 30 to 60 years 13
  • Bilateral vestibular schwannoma with coexisting neurofibromatosis type 2 typically develops in adolescence or early adulthood 9
Genetics
  • Bilateral vestibular schwannoma is a hallmark feature of neurofibromatosis type 2 (OMIM #101000 147 9
    • Inherited in an autosomal dominant fashion 6
Other risk factors/associations
  • Exposure to ionizing radiation is the only known risk factor for developing unilateral vestibular schwannoma 15

Diagnostic Procedures

  • From Wu H et al: Summary and consensus in 7th International Conference on acoustic neuroma: an update for the management of sporadic acoustic neuromas. World J Otorhinolaryngol Head Neck Surg. 2(4):234-9, 2016, Figure 1.Main grading systems for acoustic neuromas. – The classifications on the left side (blue area) are mainly based on tumor size, whereas those on the right side (green area) are based on the anatomic relationship around the tumor. Koos classification combines the tumor size and anatomic relationship for larger tumors. CPA, cerebellopontine angle; IAC, internal auditory canal.

Primary diagnostic tools

  • Suspect diagnosis based on history and auditory test results 16
  • MRI of brain and internal auditory canal is indicated to confirm diagnosis and define tumor anatomy 17

Imaging

Functional testing

Differential Diagnosis

Most common

  • Meningioma
    • Tumor originating from brain meninges (typically benign)
    • Hearing loss is less common than in vestibular schwannoma
    • Differentiated by more homogeneous appearance on MRI with broad dural base, calcification, and absence of internal auditory canal involvement
  • Epidermoid tumor or inclusion cyst
    • Tumor or cyst found on skin, sometimes near ear (typically benign)
    • Hearing loss is less common than in vestibular schwannoma
    • Differentiated by lack of contrast-enhancement component on MRI and restricted diffusion of diffusion-weighted MRI
  • Facial nerve schwannoma
    • Tumor originating from Schwann cells of the facial nerve
    • Facial weakness is prominent and occurs early
    • Differentiated by imaging; results show enhancement extending into geniculate ganglion of facial nerve and canal
      • MRI is the preferred imaging technique for all schwannomas 20
      • High resolution thin section bone CT of temporal bone is helpful to assess otic capsule for bone scalloping and remodeling caused by tumor 20
  • Trigeminal schwannoma
    • Tumor originating from Schwann cells of the trigeminal nerve
    • Facial numbness is prominent
    • Hearing loss is less common than in vestibular schwannoma
    • Differentiated using MRI, which demonstrates involvement of petrous apex and extension into Meckel cave
      • Does not extend into internal auditory canal

Treatment

  • From Rhoton AL Jr et al: Microsurgical anatomy of acoustic neuroma. 2002. Neurosurg Clin N Am. 19(2):145-74, 2008, Figure 11AB.Middle fossa approach for removing a small vestibular schwannoma (continued). – (A) Left side. The vertical skin incision is located anterior to the ear and the craniotomy is situated with its base on the floor of the middle cranial fossa (stippled area). (B) The dura is elevated from the floor of the middle cranial fossa to identify the greater petrosal nerve (Petrosal N.). The middle meningeal artery (Mid. Men. A.) courses on the dura. Bone is removed over the greater petrosal nerve (Petrosal N.) to expose the facial nerve (Facial N.) which is followed proximally by removing bone to expose the superior wall of the internal auditory canal. Extreme care must be taken to avoid injuring the semicircular canals located in the bone at the posterior margin of the exposure and the cochlea situated in the bone just anterior and deep to the facial nerve.
  • From Rhoton AL Jr et al: Microscurigal anatomy of acoustic neuroma. 2002. Neurosurg Clin N Am. 19(2):145-74, 2008, Figure 11CD.(continued) Middle fossa approach for removing a small vestibular schwannoma. – (C) Enlarged view of the area of bone removal. The dura has been opened to expose the tumor in the internal auditory canal (Int. Auditory Canal). The tumor arises in the superior vestibular nerve (Sup. Vestibular N.) and displaces the facial nerve anteriorly. (D) The superior vestibular nerve has been divided above the transverse crest and elevated with the tumor. The superior vestibular nerve is being divided medial to the tumor. The facial, cochlear (Cochlear N.), and inferior vestibular (Inf. Vestibular N.) nerves are preserved.

Goals

  • Slow growth of or eliminate tumor
  • Slow or prevent symptom progression

Disposition

Recommendations for specialist referral

  • Refer to neurosurgeon for evaluation and treatment planning
  • Refer to radiation oncologist if neurosurgeon recommends stereotactic radiosurgery

Treatment Options

Therapeutic options are based on tumor characteristics (eg, size), hearing status, and patient’s general health

  • Observation with periodic MRI surveillance is recommended for older patients with small tumors (less than 1 cm in diameter) 2 1 who are poor candidates for surgery or radiotherapy and for patients with small tumors and no significant symptoms 24 25 21 22 23
    • Most patients develop progressive hearing loss owing to slow growth of tumor thus observation may not be appropriate if hearing preservation is important 18 22
    • May consider administering aspirin to patients undergoing observation 25
  • Radiotherapy (either single session or fractionated stereotactic radiotherapy) 29 is recommended for small to medium (less than 3 cm in diameter) 2 1 tumors 26 27 28
    • Provides excellent local tumor control for smaller tumors (comparable to that of surgery); however, long-term outcomes (longer than 20 years) have not been established 16 30
    • Lower risk for acute complications (eg, cranial nerve injury) and greater preservation of hearing compared with surgical resection 27 30
    • Not usually appropriate for larger tumors (more than 3 cm in diameter 1 2) as they are associated with risk of brainstem compression due to posttreatment edema 18
    • Radiotherapy outcome for acoustic neuromas.GradeDescriptions1Tumor control, tumor diameter is reduced by more than 2 mm, and the volume is reduced by more than 10%2Tumor stability, tumor diameter reduction is less than 2 mm, and the volume reduction is less than 10%3Tumor growth, the tumor does not shrink or tumor size re-increases after shrinking View full sizeCitation: From Wu H et al: Summary and consensus in 7th International Conference on acoustic neuroma: an update for the management of sporadic acoustic neuromas. World J Otorhinolaryngol Head Neck Surg. 24;2(4):234-9, 2016, Table 3.
  • Microsurgical resection is effective for most tumors, in particular those larger than 3 cm in diameter 27 28
    • Subtotal resection allows maximal functional preservation because it minimizes cranial nerve damage while providing good local tumor control 18
    • Gross total resection is considered the procedure of choice for the following: 18
      • Young patients with persistent symptoms
      • Patients with small anatomically accessible tumors
      • Patients with large tumors with causing cerebellar and/or brainstem compression
  • For patients with neurofibromatosis type 2 who are not suitable candidates for surgery, treatment with bevacizumab—a recombinant human monoclonal antibody—may be an option. Lapatinib is another possible option 25 31 32
    • Radiotherapy outcome for acoustic neuromas.GradeDescriptions1Tumor control, tumor diameter is reduced by more than 2 mm, and the volume is reduced by more than 10%2Tumor stability, tumor diameter reduction is less than 2 mm, and the volume reduction is less than 10%3Tumor growth, the tumor does not shrink or tumor size re-increases after shrinking View full sizeCitation: From Wu H et al: Summary and consensus in 7th International Conference on acoustic neuroma: an update for the management of sporadic acoustic neuromas. World J Otorhinolaryngol Head Neck Surg. 24;2(4):234-9, 2016, Table 3.

Drug therapy

  • Vascular endothelial growth factor–A inhibitor 31
    • Bevacizumab
  • Tyrosine kinase inhibitor
    • Lapatinib 32

Nondrug and supportive care

Procedures
Stereotactic radiosurgery or fractionated stereotactic radiotherapy

General explanation

  • Minimally invasive outpatient procedure involving delivery of precisely targeted radiation to tumor site using 3-dimensional imaging guidance 33
    • Stereotactic radiosurgery (gamma knife radiosurgery) involves delivery of a single high dose of radiation to the tumor site
      • It is recommended that, for single fraction stereotactic radiosurgery doses, less than 13 Gy be used to preserve hearing and to minimize new onset or worsening of preexisting cranial nerve deficits 25
    • Fractionated stereotactic radiotherapy consists of delivery of the radiation dose over a series of treatment sessions

Indication 16

  • Small (less than 1 cm in diameter 2 1) to medium (less than 3 cm in diameter 1 2) tumors 1
  • Patients for whom surgery is not a viable option owing to age or other risk factors

Contraindications

  • Relative contraindications 16 22
    • Larger tumors (more than 3 cm 1 2) causing brainstem or cerebellar compression (due to complications associated with possible posttreatment swelling) 21
    • Young age (due to current lack of data regarding long-term outcomes)

Complications 34

  • Cystic degeneration
  • Tumor growth
  • Facial paralysis or numbness
  • Malignant transformation of tumor (very small risk) 23 33
Microsurgical resection of tumor

General explanation

  • Complete surgical removal of tumor 10 16
  • Surgical approach varies based on size of tumor and hearing status
    • Includes suboccipital, translabyrinthine, or middle fossa approaches
  • Extent of removal is determined by tumor size and degree of association with facial nerve
  • If microsurgical resection is necessary after stereotactic radiosurgery, it is recommended that patients be counseled regarding increased likelihood of subtotal resection and decreased facial nerve function 25

Indication

  • All tumors 35
    • Preferred for large tumors (more than 3 cm 2 112

Complications

  • Cerebrospinal fluid leak
  • Meningitis or other infection
  • Facial numbness or paralysis

Comorbidities

  • Neurofibromatosis type 2
    • Present in 5% of all patients with vestibular schwannoma 4
    • Present in almost all patients with bilateral vestibular schwannoma 36

Monitoring

  • When choosing to observe existing tumor (watch and wait), obtain MRIs annually for 5 years, and lengthen interval thereafter as tumor proves stable 25
  • Regularly follow-up with MRI monitoring every 6 to 12 months to assess for any change in tumor size or recurrence after treatment. Annual MRI scans may be reasonable for 5 years in patients not receiving gross total resection 25 12

Complications and Prognosis

Complications

  • Worsening tinnitus and hearing loss
    • Tinnitus grading system for vestibular schwannomas.GradeDescriptionsINo tinnitusIIIntermittent or mild tinnitus, can only be heard when the ambient noise is lowIIIPersistent or moderate tinnitus, can be heard every dayIVPersistent and severe tinnitus, interfere with work and sleep View full sizeCitation: From Wu H et al: Summary and consensus in 7th International Conference on acoustic neuroma: an update for the management of sporadic acoustic neuromas. World J Otorhinolaryngol Head Neck Surg. 24;2(4):234-9, 2016, Table 1.
  • Persistent vertigo and dysequilibrium
  • Cranial neuropathies (eg, facial weakness or numbness, swallowing problems)
  • Persistent headaches
  • Tumor recurrence
  • Hydrocephalus
  • Brainstem compression causing death
  • Gait ataxia and motor paralysis

Prognosis

  • Vestibular schwannomas are slow-growing, benign tumors that do not metastasize. Prognosis is typically good 16
    • Some vestibular schwannomas demonstrate no significant growth for long periods after they are identified 22
  • Majority of small to medium tumors can be controlled by all treatment modalities 35
  • Complete surgical removal of tumor is feasible in many patients; however, in some situations, residual tumor must be left in order to preserve facial nerve motor function
  • Low rates of recurrence, mortality, and major disability are reported in patients who undergo surgical treatment 21
  • Permanent hearing loss is common, regardless of treatment modality 7
  • Small proportion of patients may experience considerable disability as a function of treatment or disease complications
    • Complications include: 4 13
      • Permanent tinnitus and hearing loss (30%-40%)
      • Headache, facial, and trigeminal neuropathies (5%-10%)
      • Vestibular dysfunction
      • Gait ataxia

Screening and Prevention

Screening

At-risk populations

  • Patients with neurofibromatosis type 2 are at increased risk of developing vestibular schwannoma, but no formal screening schedule or recommendations exist

Screening tests

  • Screening consists of internal auditory canal protocol MRI with contrast medium and audiometry testing

Sources

1 Wu H et al: Summary and consensus in 7th International Conference on acoustic neuroma: an update for the management of sporadic acoustic neuromas. World J Otorhinolaryngol Head Neck Surg. 2(4):234-9, 2016 Reference