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FRCS Part 1 > Ch40 Tumours of cranial, spinal and peripheral nerves > Flashcards

Ch40 Tumours of cranial, spinal and peripheral nerves Flashcards

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1
Q

Which nerve do vestibular schwannomas arise from?

A

Inferior division of the vestibular nerve (not the cochlear nerve!)

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2
Q

What is the function of schwannomin / merlin?

A

A tumour suppressor gene involved with cytoskeleton:membrane binding

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3
Q

What proportion of VS are unilateral?

A

95%

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4
Q

Which patients should undergo genetic screening for NF2?

A

Unilateral VS and <40 years

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5
Q

What is the difference between VS from sporadic cases compared to NF2?

A

Sporadic cases displace the CN8 whilst in NF2 they form grape-like clusters that infiltrate the nerve.

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6
Q

What are the histological subtypes of vestibular schwannomas?

A

Antoni A (narrow elongated bipolar cells) and Antoni B (loose reticulated). Verocay bodies (eosinophilic areas surrounded by spindle shaped schwann cells) are also seen.

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7
Q

What is the presenting triad of VS?

A

Ipsilateral sensorineural hearing loss Tinnitus Imbalance Large tumours go on to cause brainstem compression (facial numbness > weakness > diplopia) / hydrocephalus.

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8
Q

What is the cause of hearing loss with VS?

A

Initially thought to be stretch on the CN8, but new evidence suggests secretion of toxic factors causing cochlear damage

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9
Q

What is the hearing loss pattern with VS?

A

Gradual and insidious. 70% have high-frequency loss causing high pitch tinnitus and word discrimination is affected more.

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10
Q

What are the causes sensorineural hearing loss

A

Tumour, infection, toxin, vascular and autoimmune

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11
Q

Why does CN5 palsy occur before CN7 with VS?

A

As sensory fibres are more vulnerable to compression than motor fibres

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12
Q

What is the earliest clinical finding with VS?

A

SNL hearing loss

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13
Q

What are the examination findings in patients with VS?

A

SNL hearing loss (66%) Loss of corneal reflex (33%) Nystagmus (26%) Facial numbness (26%) Facial weakness (12%) Diplopia (11%) Papilloedema (10%) Babinski sign (5%)

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14
Q

Explain the Rinne’s and Weber’s test with VS?

A

Weber - tuning fork at vertek > localises to the contralateral side Rinne’s - positive i.e. air>bone conduction on both sides

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15
Q

What is the House-Brackmann grading system (1985)?

A

1 = normal 2 = mild dysfunction with normal symmetry at rest but slight weakness 3 = moderated dysfunction with non-dyfiguring asymmetry. Complete eye closure with effort. 4 = Moderate to severe dysfunction = dysfiguring asymmetry with incomplete eye closure 5 = Barely perceptible motion 6 = No movement

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16
Q

What is the differential diagnosis of a CP angle lesion?

A

VS Meningioma Schwannoma of an adjacent cranial nerve e.g. CN5 or 7 Arachnoid cyst Epidermoid Metastasis Aneurysm Neurenteric cyst

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17
Q

How would you investigate a patient with a CP angle lesion?

A

MRI +/- contrast with CISS/FIESTA CT Audiometry (PTA / Tymps / speech discrimination) If small VS (<1.5 cm dia) then ENG / VEMP / ABR.

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18
Q

What are the Electronystagmography (ENG)?

A

Electronystagmography - use to assess superior vestibular nerve function through cold and warm water (bi-thermic caloric testing in the ear causing nystagmus = (COWS) cold opposite warm same) . Note this only tests the horizontal semicircular canal.

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19
Q

What are VEMPs?

A

Vestibular evoked myogenic potentials. Most commonly recorded in SCM. These assess the inferior vestibular nerve through delivery of acoustic energy the saccule and is independent of hearing function so can be performed if completely deaf..

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20
Q

Interpret this ENG result:

A

Reduced superior vestibular nerve function in the right ear on cold caloric testing.

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21
Q

What are BAERs?

A

Brainstem auditory evoked responses. In VS results in prolonged I-III interpeak latencies. Useful for prognostication as poor wave morphology corresponds to lower chance of preserving hearing even with good pre-op hearing.

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22
Q

Which patients should be screened for a VS?

A

>10dB symmetric sensorineural hearing loss at >2 frequencies, asymmetric tinnitus (positive yield <1%!) or sudden sensorineural hearing loss in one ear.

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23
Q

What is the audible spectrum?

A

500-2k Hz

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24
Q

What do the X, O and triangles denote on a PTA?

A

X = Left

O = Right

and Triangle = bone conduction

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25
How do you differentiate high freq hearing loss from a VS compared to hearing loss with age or loud noise?
VS hearing loss is asymmetric whilst other causes are symmetric
26
Which type of hearing loss has most effect on speech discrimination?
Retrocochlear hearing loss (note speech discrimination maintained with conductive hearing loss)
27
How is serviceable hearing defined?
Modified Gardener-Robertson - PTA loss \<50 dB and speech discrimination \>50% serviceable Pragmatically: 1 = may use a phone on that side, 2 = can localise sound
28
Why are CISS/FIESTA useful for VS workup?
Visualise the course of the facial nerve and surrounding CNs if involved
29
What do hyperintense T2 regions of a VS suggest about the tumour?
That these tumours are softer and suckable so result in better CN VII function.
30
How do you grade the tumour extent of VS?
1 = intracanalicular (\<0.5 cc) 2 = Protrusion into CPA (\<1 cc) 3 = Extends to brainstem but does not displace it (\<2 cc) 4 = Displaces the brainstem and cranial nerves (4 cc)
31
Why should you order a thin CT for pre-op VS planning?
Middle fossa - geniculate ganglion position and identify dehsicence Translab - pneumatisation of the mastoid and position of the sigmoid sinus and jugular bulb (high riding) Retrosigmoid - Bone coverage over the posterior semicircular canal and pneuomatisation of the retrofacial region (CSF leak risk).
32
What are the management options for VS?
1. Conservative - watchful waiting 2. Radiosurgery - single dose SRS with \<13Gy is recommended for hearing preservation 3. Surgery 4. Biological therapies - Anti-VEGF (Avastin) for NF-2 related VS
33
Which VS have a faster growth rate with conservative management?
Those that expand outside of the IAC
34
Which tumours had a lower hearing preservation rate and high risk of CN7 injury?
\>15 mm diameter
35
Which VS may demonstrate sudden and dramatic growth?
Cystic tumours
36
What are the CNS practice guidelines for the management of Koos 1 VS (intracanalicular) without tinnitus?
Observation - as these have a lower rate of growth and better hearing preservation.
37
What are the hearing preservation rates with SRS?
25-50% @ 10 years for serviceable hearing pre-SRS
38
Is there grade 1 evidence for the management of VS?
No!
39
What is your management algorithm for VS?
Koos 1/2 with intact hearing - conservative and treat only if \>2 mm growth between 6 monthly MRI Koos 3 - treatment with SRS or surgery Koos 3/4 - Surgery to reduce the mass effect and decompress the brainstem
40
What is the difference in hearing preservation between SRS and surgery for VS?
At 5 years SRS is better but at 10 years it is the same. The hearing preservation with SRS is dependent on the amount of radiation given to the cochlear. With surgery experience and use of cochlear monitoring improves hearing.
41
What is the rate of facial nerve preservation?
98% overall with Koos 1-2. With SRS it is also good if 13Gy is given (but not 20Gy)!
42
What is the risk of developing trigeminal neuralgia with SRS for VS?
7% with the higher dose of 20Gy, but no patients developed it if 13Gy was used.
43
What % of SRS treated VS increase in size?
20% show pseudo growth at 8 months, but the retreatment rate at 5 years was 4% (same as surgery)
44
How do you treat vertigo associated with VS?
Self limiting and improves with vestibular rehab exercises
45
Which surgical approaches are best for hearing preservation?
If small and intracanalicular then middle fossa. All others should be treated by retrosigmoid
46
Which nerves should be monitored during VS surgery?
CN7 and 8. CN8 monitoring can be direct or via BAERs
47
What is the difference between serviceable and salvageable hearing?
Serviceable = 50/50 rule with PTA \<50dB and \>50% speech discrimination score Salvageable hearing is whether serviceable hearing will be preserved post-op. This is unlikely if the pre-op speech discriminiation score \<75%, PTA losses at \>25%, tumour \>2 cm or the pre-op BAER are abnormal.
48
Who performed the first VS resection?
First performed by Charles Ballance (NHNN) in 1894
49
Which direction is the facial nerve displaced with VS?
Forwards 75% \>Inferior\>Posterior
50
Where is the cochlear nerve found in VS surgery?
10% as a separate band on the tumour surface 90% within the tumour!
51
What is the goal of VS surgery if the tumour is tightly adherent to the CN7 or brainstem?
Subtotal / near-total resection leaving a small cuff on the nerve followed by SRS
52
How do you treat hydrocephalus associated with a VS?
VP shunt followed by surgery ~2 weeks later or EVD at start of surgery
53
Describe the middle fossa approach.
Lumbar drain Head horizontal 6 cm incision starting ant to the tragus 4x3 cm craniotomy Subtemporal extradural approach - section MMA and preserve the GSPN Drill and expose the IAM from the meatus to Bill's bar Localise CN7 with stimulator Open the dura over the IAM and dissect tumour from CN8
54
Describe the translabyrinthine approach.
Supine head turn Prep abdo for fat graft C-shaped skin incision behind pinna to allow exposure of sigmoid Mastoidectomy and preserve facial canal Drill through vestibular apparatus behind and superior to CN7 The dura bounded by the sigmoid sinus, sup. petrosal sinus and deep to the labyrinthine is Trautman's triangle. Open the dura to get access to the posterior lateral brainstem.
55
Label the anatomy of the pre-sigmoid approach
A- Sinodural angle B- Trautman's triangle C- Sigmoid sinus D- Jugular bulb E- Facial nerve (mastoid segment / tympanic segment) F- Semicircular canal
56
How do you open the dura for a translabyrinithine approach?
57
Describe the retrosigmoid approach.
Lateral position - mayfield Lumbar drain C-shaped incision 3 cm behind the pinna Identify asterion and then transverse-sigmoid junction with craniotomy C- Durotomy with release to angle between transverse-sigmoid junction Sacrifice the petrosal vein to allow cerebellum to fall away Exposure to CPA and cisterna magna for CSF release Identify tumour capsule and perform CN7 monitoring during resection
58
CT anatomy for approaches to VS
Important not to enter the Superior semicircular canal when entering the IAM during a retrosigmoid approach otherwise they will lose hearing. Drill anterior to the endolymphatic canal
59
How do you manage facial nerve dysfunction following VS surgery?
Lacrilube, eye taping at night. If complete loss then tarsorrhaphy within a few days. Facial reanimation with CN12-CN7 anastamosis 2 months after CN7 nerve was divided.
60
What are the routes for CSF leak following VS?
1. Apical to the tympanic cavity (most common) 2. Vestibule of the horizontal semicircular canal 3. Posterior semicircular canal 4. Perilabyrinithine cells \> Mastoid air cells 5. Mastoid air cells during craniotomy
61
Where is the vestibule of the semicircular canal?
Where all of the semicircular canals join. The oval window opens into the vestibule.
62
What is attached to the oval window?
The footplate of the stapes. Note: the round window is between the middle and inner ear and covered with a membrane.
63
What is the risk of malignant transformation with SRS for VS?
3 in 1000
64
What is a perineurinoma?
Tumour composed exclusively of neoplastic perineural cells. Causes pseudo-onion bulb formation with cylindrical enlargement of the nerve over 2-10 cm. Can be grade 1-3.
65
What % of MPNST are associated with NF1?
50%. In NF1 they tend to occur in plexiform or intraneural neurofibromas
66
What is the action of Bevacizumab?
VEGF inhibitor
67
What is the action of Erlobtinib / Debrafnib etc?
Tyrosine kinase pathway inhibitors affecting the BRAF pathway (RAS\>RAF\>MEK\>ERK)
68
How does cisplatin work?
Platinum Alkylating agent
69
How do everolimus / serolimus / rapamycin etc work?
mTOR inhibitors
70
What is the mTOR pathway?
Tyrosine kinase R \> PIP2 conversion to PIP3 by PI3K \> Akt \> TSC-1 and 2 \> mTOR \> transcription factors for cell replication
71
How does vincristine work?
Microtubule inhibitor
72
Which chemotherapy agents are alkylating agents?
Carmustine Cisplatin Lomustine Procarbazine Temozolamide
73
What are the features of cystic VS?
More rapid growth Frequent CN7 involvement Unpredictable biological behaviour Heamorrhage into the cyst esp after SRS may be associated with brainstem compression and obstructive hydrocephalus
74
What is a marginal sinus?
A sinus that runs on the inner aspect of the foramen magnum
75
What are the boundaries of Trautmann's triangle?
Superior petrosal sinus above Sigmoid sinus behind Jugular bulb below Semicircular canal anterior
77
What SRS dose is given to vestibular schwannomas?
12Gy. Not 16 Gy is associated with facial nerve injury in 1/3!
78
Is there any difference in facial nerve palsy rates with approach to VS?
Middle fossa approaches are associate with a higher facial nerve palsy rate, but there is no difference between retrosigmoid and translabyrinthine approaches.
79
What HB grading has the best outcome from facial reanimation therapy?
HB3 Options include face-lift/eyelid tarsorrhaphy facial anastomosis
80
What is the management of a parasellar meningioma causing visual impairment?
Decompression of the optic nerve Resection of the extracavernous portion compressing the CN2 SRS to the remainder
81
What is the blood supply to anterior skull base meningiomas?
Ethmoidal arteries Opthalmic A branches ACA branches if very large
82
How do you differentiate chordomas and chondrosarcomas?
Indistinguishable on MRI. Classic soap bubble appearance. Chordomas arise from the midline whilst chondrosarcomas arise paramedian. Chordomas sacral 50%, clival 35% and vertebral 15%
83
What jugular foramen syndromes affect CN9/10/11?
Vernet = 9/10/11 Collet-sicard = 9/10/11/12 Villaret = 9/10/11/12/Sympathetics
84
How do you distinguish a TSH-adenoma from TSH resistance as both result in a high TSH with high/normal T4?
The alpha-subunit ratio to TSH ratio \>5.7 is diagnostic for TSH tumour
85
What is the alpha subunit of TSH?
This is a glycoprotein G-protein subunit on Ch6 that is common to HCG, FSH, LH and TSH. The beta-subunit is what responsible for the biological effects. A raised alpha subunit: TSH ratio is indicative of a TSH adenoma
86
What are the contents of foramen lacerum?
Carotid GSPN / Vidian nerve Ascending pharyngeal artery Emissary vein
87
What is a transcochlear approach?
Drilling of the superior and posterior EAM The sacrifice of the semicircular canals and cochlear Rerouting the facial nerve to access the CPA, petrous apex and ventral brainstem

FRCS Part 1 (85 decks)

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