Vestibular schwannoma

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Status

Done

General

Do not use acoustic neuroma: as most do not come from acoustic "cochlear nerve"

Most common at superior division of vestibular nerve

Numbers

Incidence of 1 per 100,000 per year

8% of primary brain tumors,

80% of CPA lesions;

Classification

Tumour size classification

Tumor size (CPA maximum diameter)	Sterkers	House	Koos	Samil	Tumor Description
0 (Intracanalicular)	Tube type	Intracanalicular	Grade I	T1	Confining to IAC
≤10 mm	Small	Grade 1 (Small)	Grade II	T2	Surpassing IAC
≤15 mm	Small	Grade 2 (Medium)	Grade II	T3a	Tumor occupying CPA
≤20 mm	Mild	Grade 2 (Medium)	Grade II	T3a	Tumor occupying CPA
≤30 mm	Mild	Grade 3 (Moderately Large)	Grade III	T3b	Tumor occupying CPA and contacting the brain stem without compression
≤40 mm	Large	Grade 4 (Large)	Grade IV	T4a	Tumor compressing the brain stem
>40 mm	Huge	Grade 5 (Giant)	Grade IV	T4b	Severe brain stem displacement and deformation of the fourth ventricle under tumor compression

Koos

Mainly for SRS usage

Do not SRS for Stage IV

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Aetiology

Sporadic

Usually 40-60 yr old

Cystic subtype is more aggressive

NF2

Merlin gene inactivation

Diagnostic criteria see tumour syndrome page

Pathology

90% arise at inferior division of vestibular nerve

Look at schwannoma

Origin

Proliferation of schwannn cells

91% - inferior division

Sensory nerve are more heavily myelinated

Obersteiner-redlich zone

CN – proximal nerve sheath formed by oligodendrocytes as they exit brain parenchyman

Transition zone between central and peripheral myelin (oligodendrocyte-schwann cell junction) is where the tumour is thought to arise from

For VIII nerve glial-Schwann cell junction (Obersteiner – Redlich) is near the porous acousticus
Within mm transition to myelin forming Schwann cells

Near the porous acoustics

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Clinical features

Bilateral vestibular tumours are the hallmark of NF2

Triad

Hearing loss (unilateral)
High pitch tinnitus
Disequilibrium (vertigo)

None/incidental

Intracanicular:

Gradual unilateral hearing loss (occasionally acute)

Sensorineural
5% have normal hearing at diagnosis
Injury to cochlear nerve causes progressive loss, sudden loss may be vascular phenomenon

Tinnitus
Vertigo

Cisternal:

Headache may be present
Worsening hearing loss
Vertigo diminishes (vestibular function lost)

Brainstem compression

CN structure:

Facial weakness

The House-Brackmann scale is a facial nerve grading system, at one end of the scale there is normal facial nerve function and at the other there is complete paralysis.

Grade	Function Level	Symmetry at Rest	Eye(s)	Mouth	Forehead
I	Normal	Normal	Normal	Normal	Normal
II	Mild	Normal	Easy and complete closure	Slightly asymmetrical	Reasonable function
III	Moderate	Normal	With effort, complete closure	Slightly affected with effort	Slight to Moderate movement
IV	Moderately Severe	Normal	Incomplete closure	Asymmetrical with maximum effort	None
V	Severe	Asymmetry	Incomplete closure	Minimal Movement	None
VI	Total Paralysis	Total Paralysis	Total Paralysis	Total Paralysis	Total Paralysis

CN V

Numbness or pain
Loss of corneal reflex

Ataxia
Nystagmus

Vestibular nerve compression: fast phase of nystagmus away from lesion
Cerebellar compression: fast phase of nytsagmus toward lesion
Brun's

Hydrocephalic

Typical headache
Visual loss
Lower CN dysfunction
Papilloedema

Investigation

Hearing assessment

Pure tone audiometer

Asymmetric high frequency sensorineural loss

Reduction in air and bone conduction

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Gardner Robertson hearing classification system

50/50” rule can be used a cutoff value for serviceable hearing.

With PTA showing values <50 dB and speech discrimination with recognition of >50%.

Grade	Hearing level	Pure tone average (dB)	Speech discrimination score (%)
I	Good to excellent	0–30	70–100
II	Serviceable	31–50	50–69
III	Non-serviceable	51–90	5–49
IV	Poor	91–maximum	1–4
V	None/deaf	Non-testable	0

American academy of otolaryngology-head and neck surgery foundation hearing classification system

ªaverage of pure tone hearing thresholds by air conduction at 0.5, 1, 2 & 3 kHz

ᵇspeech discrimination at 40 dB or maximum comfortable loudness

Boldface classes are generally considered serviceable hearing.

Class	Pure tone threshold (dB)ª	Speech discrimination scoreᵇ (%)	Clinical utility
A	≤ 30	AND ≥ 70	"Useful"
B	> 30 AND ≤ 50	AND ≥ 50	"Useful"
C	> 50	AND ≥ 50	"Aidable"
D	any level	< 50	"Nonfunctional"

WHO grade of hearing impairment

Grade of Impairment	Corresponding audiometric ISO Value (better ear)	Performance
0 – No impairment	25 dB or better	No or very slight hearing problems. Able to hear whispers.
1 – Slight impairment	26–40 dB	Able to hear and repeat words spoken in normal voice at 1 meter.
2 – Moderate impairment	41–60 dB	Able to hear and repeat words spoken in raised voice at 1 meter.
3 – Severe impairment	61–80 dB	Able to hear some words when shouted into better ear.
4 – Profound impairment (including deafness)	81 dB or greater	Unable to hear and understand even a shouted voice.

Can occur in radiologically static tumours

One study from Manchester found 22% patients had hearing loss over a mean F/U of 4.6 yrs despite no radiological progression

Large tumours may have preserved hearing
Likely to lose hearing over time

Chance of maintaining serviceable hearing without surgery is

High at 2yrs
Moderate at 5yrs
Low at 10yrs

Decrease acoustic reflex
BAER

No longer used for diagnosis as expensive
Intra-operative monitoring
A characteristic finding on ABR in a person with an acoustic neuroma would be a wave I with nothing after it ABR.

DDx hearing loss in Ménière disease vs Acoustic tumor

Ménière disease:

Hearing loss fluctuates.
The brainstem auditory evoked potentials are normal in Ménière disease.

VS:

Hearing loss is progressive.
The brainstem auditory evoked potentials are abnormal in VS.

Imaging

CT

Bony landmarks

Surgical planning

Look for high riding jugular
Pneumatization of the occipital bone

Size of the internal auditory canal (IAC) and whether or not there is any dilatation of the canal.

MRI

When to MRI

Different criteria but Olson et al 2017 suggest:

>10Db interaural difference at 2+ different
Contiguous freq or > 15Db at one freq
Asymmetric tinnitus (yield < 1%)
Sudden sensineural hearing loss (yield <3%)

Gold-standard

Can see tumours as small as 1-2mm

Assess for oedema

Suggests high risk of pial violation during dissection of the tumour

Assess arterial anatomy

Relationship to basilar, AICA, PICA

Assess venous anatomy

High-riding jugular bulb
Posteriorly displaced sigmoid sinus

Assess Cranial nerve

FIESTA/CISS

Principles of management

Preserve hearing

Natural history

Unpredictable

Grow = 30-90% depending on follow up

Don't grow = 9-75%

Get smaller = 10-22%

Most that grow, do so slowly

Average growth rates reported as 1.5-2mm/year

Mean size at diagnosis has decrease

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Age and sex

Age of diagnosis has increased

No difference in growth based on age/sex

Intrameatal vs extrameatal growth

Intrameatal (intracannalicular)

83% remained intrameatal
Of those that grew:

64% grew yr 1
23% grew yr 2
5% grew yr 3
8% grew yr 4
0% after 5 years

Mean growth 10.3mm year 1
Mean growth 0.9mm year 4

Extrameatal

1% regressed
70% remained static
29% grew

Of those that grew:

62% yr 1
26% yr 2
10% yr 3
nil after yr 5

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Hearing outcomes

50% maintain hearing

For patients presenting with class A hearing at the time of diagnosis

Number of years since follow up	% maintaining Class A hearing
5 years	55
10 years	46%

Speech discrimination	% of pt with good hearing for extended period of time
100%	88%
<100%	55%

Risk of facial palsy development

Facial palsy during observation is exceptionally rare

Should raise suspicion for other less common pathologies, such as a facial nerve schwannoma or a more aggressive tumoUr variant.

Treatment

Goals

Oncological control

To preserve serviceable hearing as long as possible

And also facial nerve function

To decompress the brainstem from the pressure

Early counselling about the genetic implications, and therefore the need for lip reading and sign language training

Decision making

Small less than 1.5cm

Watch & wait

Medium 1.5 to 3cm

Watch & wait
Radiosurgery

Large more than 3cm

Surgery

Cystic lesion

Potential rapid growth

Treatment strategies

Usually MDT pathway

Radiosurgery

For tumours <3cm diameter

Surgery

Insufficient evidence underlying most practice due to

Limited good quality studies
Few studies with long term F/U
No clear consensus on criteria for the diagnosis of tumour control / treatment failure

For CN8 = Gardner Robertson 1-2
For CN7 = House Brackmann 1-2

Conservative (Watch & wait)

Indication

Ideal if small/asymptomatic or in elderly/frail
If <1.5cm, perform the following monitoring

Radiological

re-MRI at 6month then annually for 5 years before considering extending interval
More frequent for NF2

Hearing test

Trigger for intervention

Growth >2mm/year should prompt consideration of intervention
Once tumour >1.5-2cm, it is likely to continue to grow

Surgery

Surgical tips

Kobayashi S: Neurosurgery, 2004:Ten remarks for Vestibular Schwannoma Surgery

Haste makes waste

Quick and slow

Believe and doubt

No touch, no traction

Fear and fear not

Remember facial nerve always

Debulk first and see nerves

Avoid blood staining of nerves

Respect the arachnoid

Retreat at an unusual difficulty

Patient selection is important

Minimize cerebellar retraction

Debulk the tumour aggressively

Find the CN7 early

Handle the nerve gently

Get ENT involved

Approaches

	Translabyrinthine approach	Retrosigmoid approach	Middle Fossa approach - Extended Middle Fossa (kawase extension)
Indications in VS	Large tumour with non-serviceable hearing	Hearing preservation for small tumours medial IAC tumour. Giant CPA tumour/for tumours sizes between 1.5-3cm.	Hearing preservation for small intracanalicular tumors (<0.5 cm) CPA extension
Hearing	Sacrifices hearing	Depends on size of lesion	Preserves hearing
Notes	Mastoidectomy and labyrinthectomy. Tumor debulked first then dissect tumour off CN VII. -Can be impossible if: -High riding jugular bulb -Anterior sigmoid sinus -Reduced/absent contralateral sinus	Drain cisterna magna CSF Removal of PF tumour first then drill posterior IAC to identify intracanalicular tumour	Extradural + subtemporal approach to IAC
Advantages	-Early identification of facial nerve at meatal opening; -Drilling is extradural (reduces subarachnoid bone dust and risk of intracranial injury from drill); -Less postop headache; -Less dizziness in patients with vertigo -Avoids cerebellar retraction (more important in younger patients with fuller posterior fossa)	-Most versatile approach -Fewer neurological complications than MCF/TL -No tumor size limitations -Hearing preservation possible (esp in small tumours) -No abdominal fat graft required -Best posterior fossa exposure (tentorium to foramen magnum): Panoramic view of CN and vasculature for removal of large tumors	-Possibly improved access to lateral tumor extent than retrosigmoid; -Best hearing preservation rates -Bone removal prior to opening the dura -Low incidence of post-op HA -Low incidence of CSF leak
Disadvantages	-Sacrifices hearing -Limited access for very large tumors extending ventral to poru -Limited access if facial nerve courses over superior pole of large tumor; -High jugular bulb limits access to caudal tumor- may need supplementation (e.g. retrosigmoid drilling, skeletonization of jugular bulb) -Need large abdominal fat graft, higher risk of CSF leak -"Unfamiliar angle of view" -Limited Superior-Inferior exposure	-During hearing preservation, access to the lateral third of the IAC is blocked by posterior semicircular canal and vestibule; -Need to confidently assess tumor penetration in IAC preoperatively; -Cerebellar retraction; -Intradural drilling required -More postop headache due to neck muscle dissection -Higher risk post-op CSF leak risk esp after IAC drilling after dural opening -Limited visualisation of fundus of IAC -Can be difficult to access lateral one-third of IAC without violating the labyrinth	-Limited access to posterior fossa. -CPA, Tumour size limitation (except with "extended" MF approach - Kawase's). -Temporal lobe retraction (seizure, vein of Labbe stroke, aphasia) -Higher risk of facial nerve palsy for smaller tumour sizes due to unfavorable position requiring more manipulation (superior vestibular nerve origin may reduce risk)

Intraoperative adjuncts

Scheller et al 2016 - Nimodipine reduced risk of hearing loss x4 compared to control group

Facial nerve electromyography (EMG)

Stretch of CN7 by large tumours can affect sensitivity
Neurophysio: Facial nerve sti: if still working at 0.5mA then >90 percent facial intact.

Brainstem auditory evoked response potentials (BAERs)

Should be used when hearing preservation attempted

Endoscopy

No evidence but may be helpful especially in assessing intracanalicular portion

Post op follow up

Annual MRI for 5 years before considering extending interval

Tumour can regrow many years down the line

If bilateral, resection of one can lead to accelerated growth of the other

Surgical outcomes

Facial nerve

Facial nerve palsy rate 4 to 16 %

Risk factors for facial palsy in VS include

Larger tumour size

CN7 function can be preserved in only 40-50% tumours >4cm

Surgical approach type

Long-term facial nerve dysfunction risk

No different between the

Translabyrinthine approach
Retrosigmoid approach

Higher with middle fossa craniotomy.

Retrosig approaches have larger tumours and as a result may have higher risk of facial nerve palsy even compared to middle fossa approaches

CNS 2017 — level 3 evidence that surgery following SRS has a greater risk of subtotal resection and CN7 dysfunction

Preventing visual complications due to CN7 palsy

Check blink response post-op
Eye drops, patch at night
Gold weight placement within the eyelid and/or tarsorrhaphy
Scleral shields

Facial nerve reanimation

Target

Cross over from other side
Hypoglossal

If >6mo later ongoing paresis faciohypoglossal anastomosis considered after the first postoperative year

Post-op facial nerve paresis must be worse House-Brackmann grade III weakness to gain the most benefit for facial nerve reanimation surgery

Other options

Static procedures such as face-life and eyelid lifts.

Size of tumour and facial nerve palsy

Samii 2010: Follow up 2-3 years

Tumour size	CN7 HB 1-3
<4cm	91%
>4cm	75%

Hearing loss

Follow up 2-3 years

Definition of serviceable hearing

Hearing discrimination of >50% at <50dB
Class 1 or 2 for New Hannover Classification

Tumour size	Serviceable Hearing
<4cm	30%
>4cm	11%

Hearing loss in the operated ear is accelerated over normal physiologic loss.

CSF leak

Mainly for retrosigmoid approach

CSF leak rate: 10-15%

Avoided by good closure and waxing of air cells

Management of established CSF leak

Period of CSF drainage with lumbar drain
Re-opening and waxing air cells/closing dura
Mastoidectomy and fat graft

Tinnitus

Worsens in 6-20%, decreases in 25-60% and is unchanged in rest

In those without tinnitus pre-op, 30-50% have it immediately post-op

Headache

Thought to be related to scarring between muscle and dura

Swallowing difficulties

May risk aspiration pneumonia and require NGT

Hemorrhage/oedema

Prevent by minimizing retraction,

Good haemostasis and preventing post-op HTN

Stroke

Risk: 0.5-1%

Radiosurgery (SRS)

General

Radiosurgery — Gamma-knife/Cyberknife

No good evidence shows one is superior

Aim

Preventing growth

Often see initial increase in size
Then gets stability or reduction in size over a number of years

Dosage

Average dose of 12 Gy

Advised <13 Gy dose to prevent CN deficits

If trying to preserve hearing — max 4 Gy to cochlea

Indication

Only used if tumour <3cm diameter

Large will need more radiation, therefore increasing radiotoxicity

Poor operative candidate

Better treatment option in elderly/frail

Bilateral VS

Tumour progression/residue after surgical resection

For Koos 1-3 not Koos 4

Outcome

Takes 1 year to see effect

First 6 months still has post radiotherapy swelling

Pseudoprogression after SRS

Tumour control

95%-97% at 5 yrs

81% at 15 yrs

Malignant change

1-10/1000 cases

Hearing outcomes

Depends on

Pre-treatment hearing quality
Tumour size
Radiation dose delivered to

Cranial nerve VIII
Cochlea
Ventral cochlear nucleus

Compared to microsurgery for similar tumors, SRS shows

Better serviceable hearing preservation (50-89%)
Reduced facial nerve and trigeminal nerve toxicity (< 5%).

Years since SRS	Hearing preservation
1 yr	73%
5 yrs	50-75%
10 yrs	25-50%

Number of years since SRS	% of patients with pretreatment serviceable hearing that maintain WHO class A or B hearing
5 years	50%
10 years	25%

CN7 palsy

1-2%

Dose of radiation	% of transient facial palsy
16Gy	29%
12Gy	<1%

Trigeminal neuropathy

3% (usually only where tumour is touching CN5)

Fractionated stereotactic radiotherapy (FSRT)

Has comparable efficacy with SRS;

Some series have reported poorer hearing preservation and increased trigeminal nerve injury with SRS.

Outcome comparison between SRS and microsurgery

General

The early risk of deafness: microsurgery > SRS > observation.

Golfinos 2016:

For tumours below 2.8cm in matched cohort

golfinos2016.pdf

Serviceable hearing @ 3-4 years

Microsurgery 42.8%
SRS 85.7%

CN7 HB 1-3 @2-3 years

Microsurgery 89%
SRS 100%

Tumour control @ 4 - 7yrs

Microsurgery 97.6%
SRS 97.6%

Factors to be borne in mind when interpretating outcome data

Length of follow-up

Duration since treatment is strongly associated with the development of non-serviceable hearing for all treatment modalities

Features that make a tumor favourable for one strategy also lend themselves to better outcomes with other management modalities

(i.e. very good pretreatment hearing capacity and small tumor size are strongly associated with a greater chance for hearing preservation in the microsurgery, SRS, and observation cohorts;
Equally, large tumors, fundal impaction or inner ear invasion, IAC erosion, and poor preoperative word discrimination predict poor outcomes independent of strategy),

Bias in surgical series means also that hearing preservation surgery is offered primarily to younger patients with smaller tumors and excellent hearing (who may have done well anyway).

Medical therapies

For NF2 cases specifically

Bevacizumab can reduce tumour size or reduce rate of growth

VEGF inhibitor
In one series of 61 pts with nearly 2yr F/U, 51% showed no growth, 26% gof smaller
Hearing maintained in 86%
Risks

Hypertension
Bleeding (tumour necrosis),
Immunosuppression
Fatigue

Effect lost over time

Lapatinib

A TK inhibitor that blocks EGFR pathway to slow tumour growth
Effect lost over time

Differential Diagnoses

CPA Meningiomas

Also homogenously enhancing

Usually pre or post meatal and not centred on IAM

Usually have a broad-based Dural attachment to posterior aspect of the petrous ridge or tentorium

Can spread into the IAC but not widen it

Feature	Meningioma	Schwannoma
Dural tail	Fq	Rare
Bony reaction	Fq (osteolysis/hyperostosis)	Rare
Angle made with dura	Obtuse	Acute
Calcification	20%	Rare
Cytic/necrosis formation	Rare	10%
Enhancement	Uniform	Inhomogeneous in 32%
Extension into the internal auditory canal	Rare	80%, can enlarge porous acusticus
MRS	Alanine	Taurine, GABA
Precontrast CT attenuation	Hyperdense	Isodense
Haemorrhage	Rare	Common

Epidermoid

Similar intensity to CSF on Tl & T2

Usually non-enhancing

Restrict on DWI

Very rare

Trigeminal schwannoma

Vascular tumours (paraganglioma, Haemangioblastoma and Solitary fibrous tumour)

Lipoma

Dural based metastases

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