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CNS > Acoustic neuroma > Flashcards

Acoustic neuroma Flashcards

1
Q

What is the cell of origin for vestibular schwannomas and acoustic neuromas (ANs)?

A

The Schwann cell of the myelin sheath is the cell of origin for ANs.

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2
Q

What is the pathogenesis of AN?

A

Malfunction of gene on chromosome 22 which normally produces the protein product Merlin (tumour suppressor gene) to control the growth of Schwann cells covering the nerve –> leads to atypical proliferation of Schwann cells

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3
Q

What is the Macro appearance of AN?

A

Well circumscribed, encapsulated, cut surface is yellow-white/grey

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4
Q

Epidemiology of AN/VS?

A

M:F 1:1
8% of intracranial tumours
Median age 50-55
Incidence increases with age

Increasing incidence seen with increased used of diagnostic imaging

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5
Q

Risk factors associated with Vestibular schwannoma?

A
  • Increasing age
  • NF2 (96% of patients with NF2 will develop AN, often bilateral.)
  • NF1 (5% of patients with NF1 will develop AN, often unilateral.)
  • childhood exposure to RT
  • Hx of parathyroid adenoma
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6
Q

What part of CNVIII do VS usually arise from?

A

From the vestibular portion (as opposed to the cochlear portion)

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7
Q

What is the microscopic appearance of vestibular schwannoma?

A

Biphasic, consisting of alternating zones of:
- Antoni A; densely cellular with interlacing bundle of spindle cells
- Antoni B : hypocellular, with haphazardly arranged spindle cells in loose myxoid/hyalinised stroma

Verocay bodies (whorling or palisading of nuclei)

No/rare mitosis figures

Commonly have regressive changes -

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8
Q

IHC pattern of vestibular schwannoma?

A

S100+
SOX10+

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9
Q

Biological behaviour of vestibular schwannoma

A

Benign
Malignant transformation extremely rare (<1%)

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10
Q

Clinical presentation of Vestibular schwannoma

A

Hearing loss (in 95% but only 2/3 aware, 16% develop sudden hearing loss)

Tinnitus (63%)

Vestibular symptoms (2/3s, often mild and non specific )

Headache (12%)

Trigeminal symptoms (facial numbness/hyperesthesia/pain)

Facial nerve symptoms (facial weakness, taste disturbance)

Brainstem compression symptoms (Ataxia, hydrocephalus, dysarthria, dysphasia, hoarseness) uncommon

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11
Q

What scale can be used for facial paralysis?

A

House-Blackman facial paralysis scale

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12
Q

What scale can be used for hearing loss?

A

Gardner-Robertson

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13
Q

What are prognostic factors for Vestibular schwannoma

A
  • Baseline level of hearing loss
  • Growth rate >2.5mm/yr
  • Delay in diagnosis

Patients with growth rate >2.5mm/yr have decreased rates of hearing preservation and decreased median time to total hearing loss

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14
Q

What surprising factor is not actually prognostic?

A

Initial tumour size

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15
Q

What is the gold standard investigation for work up of VS?

A

MRI with contrast

High resolution CT with IV contrast if MRI contraindicated

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16
Q

What are the classic MRI appearances of a VS?

A

Isointense/hypointense signal on T1, with homogeneous contrast enhancement

“Ice cream cone shape” with widening of porus acousticus (the medial opening of the internal acosutic canal through which CN VII and VIII pass)

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17
Q

What are the differentials for VS?

A

Meningitis
Glomus tumour
Ependymoma
Facial or Trigeminal schwannoma
Epidermoid cyst
Metastases

18
Q

What system is used to grade VS?

A

Koos grading scale based on location/relation to brainstem

No staging system for VS

19
Q

Describe Gr 1-IV of Koos grading scale for VS

A

Grade 1- intracanalicular

Gr2- tumour extending into posterior fossa, not touching brainstem

Gr3- touching/compressing brainstem but not shifting from midline

Gr4- compressing and shifting brainstem from midline

20
Q

What are the management options for vestibular schwannoma?

A

Observation
Surgery
Radiotherapy

21
Q

Who is observation favoured for?

A
  • Patients without hearing loss (as treatment runs risk of causing hearing loss)
  • stability or slow rate of growth
  • Elderly patients with comorbidites
22
Q

What features would indicate treatment is needed rather than continued observation with a Vestibular schwannoma?

A

> 2.5mm growth/year
Or
Onset or worsening of symptoms

23
Q

What is the role of systemic treatments in VS?

A

Generally no role of systemic treatment but bevacizumab has shown response in rare progressive situations with NF2

24
Q

Who is appropriate for surgical management?

A
  • Young patients
  • Large tumours
  • Tumours causing mass effect or dizziness
  • Cystic tumours
  • Small anatomically favourable tumours with good hearing
25
Q

What are the main disadvantages of surgery?

A

Poor outcomes for hearing preservation (hearing likely better if tumour <2cm)

Complications of surgery:
CSF leak
Tinnitus
Headache
Facial paralysis

26
Q

What are the advantages of surgical resection?

A

-excellent results for resection of entire tumour
- immediate symptom relief if compressive symptoms
- one off procedure

27
Q

When is radiotherapy appropriate for VS?

A

Preferred for Tumours <4cm in size,
Unresectable,
Patient declined surgery or medically inoperable

28
Q

What radiotherapy options are available?

A

Stereotactic radio surgery

Fractionated stereotactic radio surgery

VMAT with conventional fractionation

Modalities;
Linac based
Gamma Knife
Protons

29
Q

What is the dose used for SRS?
Who is this appropriate for?

A

12.5GY/1#

Appropriate for tumours <2cm (defs not >3cm )

30
Q

What are doses used for fractionated stereotactic RT?

A

21Gy/3#

Or 25GY/5# if >2cm

31
Q

What is a VMAT conventional dose?
When is this a good idea?

A

50.4Gy/28#

Good if close to OARs

32
Q

What are the rates of hearing preservation after surgery ?

After RT?

A

After surgery 0-25% hearing preservation

After RT:
@2 years 75-10%
@10years 50% (confounded by aging)

33
Q

Describe contours for radiotherapy of Vestibular schwannoma

A

GTV = gross disease
- volumes on T1 post contrast (appears hyper intense)
- CT head with boney windows for delineation of internal auditory canal

CTV = GTV as benign so no expansion

PTV = 3mm expansion

34
Q

What follow up is required for patients on observation?

A

Audiometry and MRI with contrast Q6-12mo

35
Q

When is surgery the preferred Tx options?

A

Surgery is preferred for large (>4 cm) symptomatic tumors or recurrence/progression after RT.

36
Q

What are the long-term LC rates after RT for ANs?

A

Long-term LC after RT for ANs is 90%–97%. (Lunsford LD et al., J Neurosurg 2005; Combs SE et al., IJROBP 2006; Litre F et al., Radiother Oncol 2013; Hasegawa T et al., J Neurosurg 2013; Maniakas A et al., Otol Neurotol 2012)

37
Q

What important AN studies prospectively compared surgery to SRS? What did they show?

A

Mayo Clinic data: <3-cm tumors, same tumor control rates but worse pt QOL after surgery. (Pollock BE et al., J Neurosurg 2006)
French data: largest prospective study. GK pts had better function overall. (Regis J et al., Neurochirurgie 2002)
Meta-analysis: included 16 studies showed SRS better long-term hearing preservation (70% vs. 50%) but no difference in tumor outcome. (Maniakas A and Saliba I, Otol Neurotol 2012)

38
Q

What are the main toxicity differences between RT and surgery?

A

RT carries a lower risk of facial nerve/trigeminal nerve injury and better rates of hearing preservation

39
Q

What IDL is prescribed in GK? Why? How about for LINAC-based SRS?

A

GK: 50% (sharpest drop off in dose is at 50% IDL)
LINAC: 80%

40
Q

What are some toxicities and rates of toxicities after SRS for ANs?

A

Trigeminal neuropathy/hyperesthesia: 0%–5%
Facial nerve neuropathy/palsy: 0%–5%
Hearing deficit: useful hearing preserved in 40%–60%

41
Q

What mean cochlea dose is the threshold for hearing preservation with SRS?

A

Mean cochlea 3 Gy. 2-yr hearing preservation 91% if mean cochlea <3 Gy vs. 59% if >3 Gy (Baschnagel J et al., Neurosurg 2013)

CNS (9 decks)

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