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HESP 632 - Medical Audiology > Lecture 12- CNS Tumors > Flashcards

Lecture 12- CNS Tumors Flashcards

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USMLE® Step 1 flashcards
1
Q

What are the 4 skull base neoplasms involving the posterior fossa?

A
  1. Common cerebellopontine angle lesions
  2. Petrous apex lesions
  3. Uncommon cerebellopontine angle lesions
  4. Inta-axial tumors
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2
Q

What are common cerebellopontine angle lesions (7)?

A
  1. Acoustic neuroma/schwannoma
  2. Meningioma
  3. Epidermoid tumor
  4. Nonacoustic neuroma/schwannoma
  5. Paraganglioma
  6. Arachnoid cyst
  7. Hemangioma
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3
Q

What is a vestibular schwannoma/acoustic neuroma?

A

Benign schwannoma of CN8

  • Most arise from vestibular division
  • Derived from schwann cells
  • Does not invade other neural structures
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4
Q

What is the site of origin of vestibular schwannoma/acoustic neuromas?

A
  • Medial portion of the IAC

- Sometimes in the CPA, lateral to the porus acusticus

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5
Q

Describe the epidemiology of vestibular schwannoma/acoustic neuromas?

A

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@

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6
Q

What are the clinical presentations of vestibular schwannomas?

A

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

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7
Q

What is the natural Hx of vestibular schwannomas?

A

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

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8
Q

What are the 3 classifications of vestibular schwannomas?

A

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

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9
Q

How are vestibular schwannomas diagnosed?

A

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

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10
Q

What is neurofibromatosis type 2 (NF2)?

A
  • 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)
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11
Q

What are neurologic manifestations of NF2?

A

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

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12
Q

What are other manifestations of NF2 (2)?

A

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
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13
Q

What is the diagnostic criteria for NF2?

A

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
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14
Q

How are vestibular schwannomas managed?

A
  1. Excision to prevent
    - Multiple cranial neuropathies
    - Brainstem compression
    - Hydrocephalus
    - Death
  2. Surgical priorities
    - Alleviate risks associated with tumor growth
    - Preservation of facial nerve function
    - Sparing of hearing
  3. Stereotactic radiosurgery- gamma knife
  4. Radiation treatment
  5. Pharmacologic treatment
    Lapatinib: targets signaling pathways of neurofibromin

Bevacizumab: targets tumor angiogenesis

Aspirin: targets inflammatory pathways

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15
Q

What are the surgical approaches for removal of vestibular schwannomas?

A

1) Retrosigmoid or suboccipital
2) Translabyrinthine
3) Middle fossa

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16
Q

What are the advantages of the retrosigmoid or suboccipital approach?

A
  • Wide exposure

- Hearing preservation possible

17
Q

What are the disadvantages of the retrosigmoid or suboccipital approach?

A
  • Increased incidence of post-op headaches
  • Higher incidence of CSF leak
  • Need for more vigorous cerebellar retraction
18
Q

What are the advantages of the translabyrinthine approach?

A
  • Wide exposure not limited by tumor size
  • Lower surgical morbidity
  • More facial nerve reconstructive options
19
Q

What are the disadvantages of the translabyrinthine approach?

A

Total hearing loss

20
Q

What are the advantages of the middle fossa approach?

A

Superior hearing preservation results

21
Q

What are the disadvantages of the middle fossa approach?

A
  • Need to retract temporal lobe

- Small tumors only

22
Q

What surgical approaches for VS are best for complete tumor resection and preservation of FN when servicable hearing is present?

A

No evidence demonstrating superiority of middle fossa vs. retrosigmoid approaches

23
Q

What surgical approaches for VS are best for complete tumor resection and preservation of FN when servicable hearing is not present?

A

No evidence demonstrating superiority of translabyrinthine vs retrosigmoid approaches

24
Q

Does VS size matter for facial and vestibulocochlear nerve preservation with surgical resection?

A

Patients with large tumors should be counseled about the greater than average risk for loss of servicable hearing

25
Q

Should small intracanalicular tumors (<1.5 cm) be surgically resected?

A

There are insufficient data to support a firm recommendation that surgery be the primary treatment for intracanalicular VSs.

26
Q

Is hearing preservation routinely possible with VS surgical resection when servicable hearing is present?

A

Hearing preservation surgery via the MF or the RS approach may be attempted in patients with small tumor size and good preoperative hearing

27
Q

When should surgical resection be the initial treatment in patients with NF2?

A

There is insufficient evidence that surgical resection should be the initial treatment in patients with NF2

28
Q

What is a meningioma?

A

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
29
Q

What are signs and symptoms of a meningioma?

A
  • Progressive hearing loss in 60%
  • Headaches
  • Imbalance
  • Tinnitus
  • Facial weakness or loss of taste
  • Diplopia or visual disturbances
  • Dysphagia
30
Q

How are meningiomas diagnosed?

A

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

31
Q

How are meningiomas treated?

A
  • 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%
32
Q

What is a facial nerve schwannoma?

A

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%)
33
Q

What are the clinical presentations of FN schwannoma?

A

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
34
Q

What are the clinical findings of FN schwannoma?

A

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

35
Q

How are FN schwannomas treated?

A

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
36
Q

How is ABR recorded in the OR?

A

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

37
Q

How are ABRs interpreted in a surgical context?

A

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
38
Q

What are direct 8th nerve action potentials (CNAP)?

A

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
39
Q

What’s the relationship between IOM and outcomes?

A

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

HESP 632 - Medical Audiology (7 decks)

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