Lecture 12- CNS Tumors Flashcards
What are the 4 skull base neoplasms involving the posterior fossa?
- Common cerebellopontine angle lesions
- Petrous apex lesions
- Uncommon cerebellopontine angle lesions
- Inta-axial tumors
What are common cerebellopontine angle lesions (7)?
- Acoustic neuroma/schwannoma
- Meningioma
- Epidermoid tumor
- Nonacoustic neuroma/schwannoma
- Paraganglioma
- Arachnoid cyst
- Hemangioma
What is a vestibular schwannoma/acoustic neuroma?
Benign schwannoma of CN8
- Most arise from vestibular division
- Derived from schwann cells
- Does not invade other neural structures
What is the site of origin of vestibular schwannoma/acoustic neuromas?
- Medial portion of the IAC
- Sometimes in the CPA, lateral to the porus acusticus
Describe the epidemiology of vestibular schwannoma/acoustic neuromas?
Diagnosis made most often between 30-60 y/o
F>M
2000-3000 diagnosed annually in USA
~95% arise de novo as a unilateral lesion
Inherited form: NF@
What are the clinical presentations of vestibular schwannomas?
Hearing related
- Unilateral or asymmetrical SNHL (95%)
- Sudden onset HL (10-20%)
- Tinnitus: high-pitched, continuous, asymmetrical
Dysequilibrium (up to 70%)
Facial hypesthesia (up to 50%)
- Most often for medium to large tumors
- Diminished corneal reflex
Headaches (40%)
- Large tumors with brainstem compression
What is the natural Hx of vestibular schwannomas?
Variable growth rates
- Average 0.2 cm/year
- 10-15% grow 1 cm/year
Three classifications
Can be fatal during a course of 5-15 years
What are the 3 classifications of vestibular schwannomas?
1) Intracanalicular (<1 cm)
2) Intracranial extention w/o brainstem distortion (1-2 cm)
3) Intracranial extension w/ brainstem distortion (>2 cm)
- BS compression
- CN5
- Hydrocephalus
How are vestibular schwannomas diagnosed?
Auditory and vestibular studies
- Impact on the functional integrity of the audiovestibular systems
Imaging studies: definitive diagnosis
Contrast enhanced MRI: gold standard
- Isointense on T1-weighted images
- Some signal increase on T2-weighted images
- Gadolinium enhancement- striking
CT with contrast
- Smoothly marginated, contrast enhancing mass for tumors over 1.5 cm
What is neurofibromatosis type 2 (NF2)?
- Multiple neoplasia syndrome
- Mutation of tumor suppressor gene - neurofibromin
- Inherited as AD trait or de novo
- Prevalence (1/60,000 people)
- Nearly 100% penetrant by age 60 years
- Phenotype: widely variable (within families less variability)
What are neurologic manifestations of NF2?
Vestibular Schwannoma
- Bilateral VS: 90-95%
- Hearing loss and tinnitus as presenting symptoms (60% adults; 30% children)
- Tumor size and rate of growth do not predict degree of HL
Meningioma: 45-58%
- 2nd most common tumor in NF2
Spinal cord ependymomas
- 18-53% of NF2 patients
- Back pain, weakness or other sensory disturbances
Peripheral neuropathy
- Most will develop
What are other manifestations of NF2 (2)?
Ocular
- Lens opacities - cataracts under age 50 years specific to NF2
- Retinal hamartomas
- Epiretinal membranes
Cutaneous
- Skin tumors in 59-68%
- Skin plaques, subcutaneous tumors and intradermal tumors
- Cafe au lait maculae
What is the diagnostic criteria for NF2?
Confirmed/definite diagnosis
- Bilateral vestibular schwannoma
Probable diagnosis - First degree relative with NF2 and either: Unilateral VS OR Two of the following: - Memingioma - Neurofibroma - Glioma - Schwannoma - Juvenile posterior subcapsular lens opacity
How are vestibular schwannomas managed?
- Excision to prevent
- Multiple cranial neuropathies
- Brainstem compression
- Hydrocephalus
- Death - Surgical priorities
- Alleviate risks associated with tumor growth
- Preservation of facial nerve function
- Sparing of hearing - Stereotactic radiosurgery- gamma knife
- Radiation treatment
- Pharmacologic treatment
Lapatinib: targets signaling pathways of neurofibromin
Bevacizumab: targets tumor angiogenesis
Aspirin: targets inflammatory pathways
What are the surgical approaches for removal of vestibular schwannomas?
1) Retrosigmoid or suboccipital
2) Translabyrinthine
3) Middle fossa
What are the advantages of the retrosigmoid or suboccipital approach?
- Wide exposure
- Hearing preservation possible
What are the disadvantages of the retrosigmoid or suboccipital approach?
- Increased incidence of post-op headaches
- Higher incidence of CSF leak
- Need for more vigorous cerebellar retraction
What are the advantages of the translabyrinthine approach?
- Wide exposure not limited by tumor size
- Lower surgical morbidity
- More facial nerve reconstructive options
What are the disadvantages of the translabyrinthine approach?
Total hearing loss
What are the advantages of the middle fossa approach?
Superior hearing preservation results
What are the disadvantages of the middle fossa approach?
- Need to retract temporal lobe
- Small tumors only
What surgical approaches for VS are best for complete tumor resection and preservation of FN when servicable hearing is present?
No evidence demonstrating superiority of middle fossa vs. retrosigmoid approaches
What surgical approaches for VS are best for complete tumor resection and preservation of FN when servicable hearing is not present?
No evidence demonstrating superiority of translabyrinthine vs retrosigmoid approaches
Does VS size matter for facial and vestibulocochlear nerve preservation with surgical resection?
Patients with large tumors should be counseled about the greater than average risk for loss of servicable hearing
Should small intracanalicular tumors (<1.5 cm) be surgically resected?
There are insufficient data to support a firm recommendation that surgery be the primary treatment for intracanalicular VSs.
Is hearing preservation routinely possible with VS surgical resection when servicable hearing is present?
Hearing preservation surgery via the MF or the RS approach may be attempted in patients with small tumor size and good preoperative hearing
When should surgical resection be the initial treatment in patients with NF2?
There is insufficient evidence that surgical resection should be the initial treatment in patients with NF2
What is a meningioma?
Lobulated, tough, white-gray mass that is well circumscribed and indents adjacent nervous tissue
- 2nd most common tumor of the CNS
- Slow growing, benign
- Extratemporal most common
- Infratemporal rare
- Female to male ratio 2:1
- Most commonly diagnosed in middle and late decades
- Often an incidentaloma
What are signs and symptoms of a meningioma?
- Progressive hearing loss in 60%
- Headaches
- Imbalance
- Tinnitus
- Facial weakness or loss of taste
- Diplopia or visual disturbances
- Dysphagia
How are meningiomas diagnosed?
Audiovestibular testing
- Cannot differentiate from AN
- Fewer abnormal ABR
MRI w/ gadolinium
- T1- isointense to slightly hypointense in relation to surrounding brain tissue
- T2- less intense than AN
- FLAIR sequences
- AN tend to involve entire IAC
- More broad based and may have calcifications
- Dural tail
CT- used to define extent of bony involvement
How are meningiomas treated?
- Locally destructive and may invade cranial nerves
- Treatment or choice: surgical excision
- Hearing preservation: more likely than AN
- Gamma knife or cyberknife
- Recurrence in up to 30%
What is a facial nerve schwannoma?
Uncommon
- 1.2% of all temporal bone tumors
- Most common intratemporal tumor sites (geniculate ganglion, IAC, labyrinthine segment)
Very slow growing
- Typically along the fallopian canal
- Otic capsule erosion (up to 30%)
What are the clinical presentations of FN schwannoma?
Facial nerve dysfunction
- Palse or twitch
- 2o compression in fallopian
Most common pattern
- Slowly progressive palsy
- Accompanied by hyperfunction
- Recurrent episodes
- Progressively worse
- May be misdiagnosed with Bell palsy
Audiovestibular signs and symptoms
- CHL with absent AR
- SNHL from cochlear invasion
- Retrocochlear
- Vertigo from a labyrinthine fistula
What are the clinical findings of FN schwannoma?
Facial nerve dysfunction: 25-50%
Mass behind the TM: 29%
MRI
- Hypointense on T1, hyperintense in T2, enhanced with gadolinium
- Enhancing enlargement of varying thickness along a large segment of the facial nerve- highly suggestive
CT
- Can identify tumor due to osseous erosion
How are FN schwannomas treated?
Surgery
- Approach varies with location
- Occasionally possible to remove and save nerve
- Nerve can be repaired with an interposition graft
- Longstanding FN palsy- poorer post-operative FN function
How is ABR recorded in the OR?
Stimulus parameters
- Rate: 20-30/sec
- High level: 95 dB pSPL or higher
Earphones: Etymotic ER10A
Electrodes: EAC linked to Cz or Fpz
- Tiptrodes
Filter settings: 300-1500 Hz
Acoustic interference during drilling
How are ABRs interpreted in a surgical context?
Anesthesia: little effect on ABR
Brain/brainstem temperature
- Absolute and interpeak latencies increase as function of decreasing temperature at 0.17-0.20 msec/degree
Craniotomy affects on ABR
- Removal of CSF
- Exposure of nerve to air
- Insertion of retractors
- Re-establish baseline after opening and placement of retractors
What are direct 8th nerve action potentials (CNAP)?
Electrode on cochlear nerve near brainstem root entry
Stimulus and recording parameters
- 64-128 trials sufficient at 20/sec
- Clicks of alternating or fixed polarity
- Lower amplifier gain
- Filters- same as ABR
Detection and interpretation of changes
- Baseline with understanding of inherent variability imperative
- Moving electrode can change response
What’s the relationship between IOM and outcomes?
Facial nerve
- Small increase in proportion with HB grade I or II
- Great decrease in incidence of HB grade V or VI
- Current standard of care in VS surgery
Cochlear Nerve
- ABR sensitivity but not specific
- Tumors <2.0 cm ~30-45% useful for adequate hearing preservation
- Success has more to do with surgical approach and identification of small tumors
- CNAP better predictor of outcome than ABR or ECoG
