Vestibular Schwannomas Flashcards
Where does a vestibular schwannoma arise?
From the Schwann cells and the sheath of the vestibular portion of the auditory nerve
Where do vestibular schwannomas originate?
The medial portion of the internal auditory canal, but also in the CPA lateral to the porus acusticus
(Moffat et al., 1993)
Describe the percentage of tumors that are vestibular schwannomas?
80% of tumors in the CPA
8% of intracranial tumors
(Brahmabhatt et al., 2016)
What s the incidence of sporadic vestibular schwannomas?
1.09/100,000 with peak age between 65-74 years of age (Kshettry et al., 2015)
What is the prevalence of sporadic vestibular schwannomas?
Between 2004-2010, 23,739 people, however the number is on the rise
How are vestibular schwannomas classified?
using the Koos morphological classification (Brahmabhatt et al., 2016)
- Stage 1–> Intracanalicular tumor <10 mm in diameter
- Stage 2–> tumor extending beyond the internal auditory meatus and a diameter <20 mm
- Stage 3–> tumor extending beyond the CPA without brainstem compression and <30 mm in diameter
- Stage 4–> diameter >30 mm causing brainstem compression
Describe the natural history of VS
Eduard Sandifort reported 1st case of VS in 1777.
Tumors grow, stay same size, shrink and growth not correlated with sex and age (Ferri et al., 2008)
Why is there variability with the tumor growth reported?
Rosenberg, 2000
Different ways to measure the size of tumors.
Proposed to use density of the tumor to measure the size, but this is expensive and not widely used.
What are the symptoms associated with a sporadic vestibular schwannoma?
- Vary based on size and location of the tumor.
- Some people are asymptomatic while others may exhibit symptoms (Ferri et al., 2008)
- Initial symptoms–> unilateral hearing loss, unilateral tinnitus, and disequilibrium (Moffat et al., 1993)
- 10% have sudden onset hearing loss (Brahmabhatt et al., 2016)
- 70% have tinnitus (Brahmabhatt et al., 2016)
What is the most common symptom associated with vestibular schwannomas?
In 90% of patients, unilateral or asymmetrical SNHL
Brahmabhatt et al., 2016
What are the vestibular symptoms associated with a sporadic VS?
- Disequilibrium
- Vertigo
- Balance problems
But the system is typically able to compensate
What other structures are affected as the tumor grows and extends out of the porus acusticus?
- Trigeminal nerve
- Cerebellum
- Brainstem
- Fourth ventricle
(Brahmabhatt et al., 2016; Moffat et al., 2016)
What other symptoms can occur as the tumor grows and begins to affect other structures?
- Depressed corneal reflex
- Hydrocephalus
- Facial pain
- Facial nerve symptoms
- Facial numbness
- Paresthesia
- Headaches
- Ataxia and unsteadiness
- Diplopia
- Hoarseness with dysphagia
(Brahmabhatt et al., 2016; Moffat et al., 2016)
What audiological tests should be completed to identify a VS?
- Behavioral audiogram
- Acoustic reflexes
- Auditory brainstem response (ABR)/ stacked ABR
What are the audiological findings on a behavioral audiogram for a patient with sporadic VS?
unilateral or asymmetric high frequency SNHL
What are the findings of acoustic reflex testing for a patient with a vestibular schwannoma?
elevated or absent and will not agree with the audiogram
What is a stacked ABR?
Don et al., 2012
An ABR that involves temporally aligning wave V of the derived-band ABRs then summing the responses.
By temporally aligning wave V of the derived-band ABRs, phase cancellation of the lower frequency activity is eliminated and the measurement reflects activity from all frequency regions of the cochlea
If a tumor is present, then the SABR amplitude will be reduced.
What vestibular tests can be completed?
ENG/VNG and calorics
True or False: The incidental identification of vestibular schwannomas has decreased.
False. It has increased due to improved technology and imaging techniques
(Anderson et al., 2000)
What is the gold standard for VS diagnosis?
contrast-enhanced MRI
Anderson et al., 2000
What is the difference between an MRI and CT scan for tumor identification?
MRI has better soft tissue resolution than a CT scan
Moffat et al., 1993
What are the management and treatment options for a patient diagnosed with a VS?
1) wait and see approach
2) gamma knife radiosurgery and stereotactic radiotherapy
3) surgical excision
4) pharmacological treatment
Describe the wait and see approach for VS management
tumor and hearing status are monitored
Due to slow growth of the tumors, this is a viable option, especially when the tumor is small (Brahmabhatt et al., 2016)
Patients who choose this option receive regular scans to monitor the tumor and ensure that there is no change in the growth.
Describe gamma knife radiosurgery
Involves taking images of the head and tumor and marking the position of the tumor.
Radiation beams are then used to enter the skull and collide on the tumor reducing/stunting it’s growth (as opposed to removing it)
Patient must still be monitored over the years.
How effective is gamma knife radiosurgery?
97.1% effective in controlling a small to medium sized tumor
Boari et al., 2014
True or false: Surgical excision involves removing the tumomr
True
True or false: Surgical excision can only be completed in isolation and not following radiosurgery.
False.
Can be completed in isolation or following radiosurgery.
What are the surgical techniques of vestibular schwannoma excision?
1) Retrosigmoid
2) Middle fossa
3) Translabyrinthine
What is the retrosigmoid approach?
AKA the suboccipital approach
Involves making an incision behind the ear to access the tumor with a path parallel to the petrous bone
What are the advantages of the retrosigmoid approach?
- Offers a wide view of the tumor and good access to the root entry zone of the auditory nerve
- Can be used for varying sized tumors
- May result in hearing and facial nerve preservation
What are the disadvantages of the retrosigmoid approach?
- Requires cerebellar retraction, which may result in motor and coordination deficits
- May be incomplete resection of the tumor
What is the middle fossa approach?
An approach that uses a superior trajectory to expose the internal auditory canal.
Unlike the post-auricular incision used in the other two approaches, a lazy s-shaped incision is made anterior to the tragus.
What are the advantages of the middle fossa approach?
- May result in hearing preservation
What are the disadvantages of the middle fossa approach?
- Can only be used for small tumors within the IAC
What is the translabyrinthine approach?
Involves making an incision behind the ear like with the retrosigmoid approach, however the tumor is accessed through the mastoid bone.
It is generally reserved for patients with poor pre-operative hearing
What are the advantages of the translabyrinthine approach?
- No need for cerebellar retraction
- Can be used for large tumors
What are the disadvantages of the translabyrinthine approach?
- No hearing preservation
What pharmacological agents have been proposed as use for vestibular schwannomas?
Aspirin (Ammoun et al., 2010)
Lapatinib (Kandathil et al., 2014)
How do these pharmacological agents work?
They target inflammation and merlin
What is merlin?
A tumor suppressor that VS patients are deficient in
