Vestibular Schwannoma Most common CPA (Cerebellopontine angle) tumor changed from prolongation of life to nerve preservation explained in brief with all pre- operative work up.

1. Presenter: Dr Fakir Mohan Sahu
SR MCh Neurosurgery
Date 20/05/2021
Facial and Hearing Preservation in
Acoustic Neuroma

2. Learning objectives
• History of Acoustic Neuroma Surgery
• Anatomy of CP angle and Cistern
• Facial and Vestibulocochlear CN anatomy
• Clinical presentation and Gradings
• Preoperative evaluations
• Intraoperative strategics for functional preservation
• Post operative rehabilitation and consideration
• Recent advances in Acoustic neuroma Surgery

3. Introduction
• Acoustic Neuroma- AKAAcoustic Neurinoma, Acoustic Neurofibroma, Vestibular Schwannoma
• Most Common intracranial schwannomas
• Arise from the transition zone of myelin (Obersteiner – Reidilich zone) at the “Porus Acousticus”
• MC arise from the inferior vestibular nerve
• Peak incidence in fourth to sixth decades
• Sporadic/ Familial, Unilateral, Bilateral (Hallmark of NF-II).

4. History of Acoustic Neuroma Surgery
• The 1st successful complete removal of Acoustic Neuroma- Sir Charles Balance(1894 )
• Harvey Cushing – Advocated Subtotal removal
• Walter Dandy (1925)- first surgeon to totally resect acoustic tumors successfully.
“ Paralysis of VII CN must be accepted as a necessary sequel of operation”
• Olivecrona (1940)–Performed surgeries by observing facial twitches to guide tumour
resection
• Rand and Kurze(1968)-Cochlear + Facial n. preservation
• Cairns (1981) First surgeon to documents facial nerve function preservation.

5. Changing trends Neuroma surgery
• Goal of surgery-
Changed from prolongation of life to CN function preservation
• Loss of function is a debilitating and psychologically devastating condition.
• According to the “Acoustic Neuroma Association”
VII CN dysfunction remains the number one concern undergoing CPA surgery
• Hearing preservation is must consider for serviceable hearing ear.
• Decision making, Intraoperative evaluation of Neuromonitoring

6. Cerebellopontine angle Anatomy
Boundaries
-Medial : Lat. Surface of brain stem
-Lateral : Petrous bone
-Superior : MCP and cerebellum
-Inferior : Arachnoid tissue of lower CN
-Posterior : Cerebellar peduncle
Contents: CSF, arachnoid tissue, CN and their
associated vessel (a)internal auditory canal,
(b) anterior is VII nerve
(c)posterior is VIII nerve
P = Pons, mcp = Middle cerebellar peduncle
CH = Cerebellar hemisphere

7. Internal acoustic meatus anatomy
• Lateral wall: superior and inferior
halves falciform crest.
• Upper compartment:
Ant. area facial nerve
Post. area superior vestibular nerve
(sharp vertical ridge- ‘Bill’s bar’)
• Lower compartment:
• Ant.Tractus spiralis foraminosus
(cochlear nerve )
• Post.Inferior vestibular nerve
(supplying the saccule)

8. Relation to IAM and Tumour Capsules
• Facial nerve-lateral end of the IAM
canal in its supero-anterior position
VIII CN -infero-lateral position
• Antero-inferior to the tumour capsule
• Facial N displacement:
Anterior 70%
Superior 10%
Inferior 13%
Posterior 7%
• Shape: Thin bundle 2/3
Splayed over capsule 1/3
The contents of the internal auditory canal can be seen
after opening the dura. C, cochlear nerve; D, dura of the
canal; F, facial nerve; HC, horizontal crest; IV, inferior
vestibular nerve; SV, superior vestibular nerve

9. Anatomical consideration of Facial nerve
• Motor(70%) and sensory (30%)components
• Branchiomotor – supplies muscle of second branchial arch
• Motor- Facial expression, Scalp, Ear
-Buccinator, stapedius, stylohyoid, Post. belly of digastric, platysma
• Parasympathetic secretory fibers-
Sublingual and submandibular salivary glands
Lacrimal gland and mucous membranes of oral and nasal cavities

10. Sensory part- Nerve of Wrisberg
• Taste--‐ Anterior 2/3 rd of tongue
• Exteroceptive--‐ Eardrum and EAC .
• Proprioceptive--‐ Muscles it supplies
• General visceral sensation--‐ salivary glands and mucosa
of nose and pharynx .
• Anatomically, motor part is separate from the sensory
and parasympathetic

11. (cisternal portion)
15.8 mm,

12. Neurophysiology
Neuron
order
Auditory pathway
Ascending auditory pathway paathway
1st Bipolar nucleus of spiral ganglion and
cochlear nerve
2nd Dorsal and ventral cochlear nuclei
3rd Superior olivary complex in pons.
From here travels in lateral lemniscus in pons
4th Inferior colliculus in mid brain
5th Medial geniculate body in thalamus
Auditory cortex (B. A 41 ,42) in temporal lobe
through the auditory radiation in sublentiform
part of internal capsule

13. Arterial Supply

14. Mechanism of
loss of function
Acoustic
Neuroma
schematic showing the possible mechanism of hearing loss in a small VS. a = fourth ventricle; b = efferent olivocochlear
tract; c = labyrinthine artery (LA); d = vestibulocochlear nerve; e = proteinaceous deposits in the inner ear fluid due to
tumor metabolism; IAF = inner ear fluid; OCB = olivocochlear bundle; OHC = outer hair cells.
Growing Tumors
Nongrowing Tumors
Early Hearing Loss
Sudden Hearing Loss

15. Pre-operative evaluation
• House-Brackmann grading system
• Tuning Fork Tests: Rinne’s, Weber’s, Schwabach test
• Audiometric Testing
• Electrophysiologic Testing- BERA, ECOG
• CT/MRI-( Size, Extension, Cystic/Solid, grading)

16. House-Brackmann grading system

17. Intraoperative facial monitoring
• Practical neurophysiology monitoring first introduced by Delgado in 1979
• Standard in VS Surgery for anatomical and functional VII preservation
• Enables instantaneous feedback on facial nerve firing during tumour dissection
• VII nerve monitoring
EMG monitoring of ms. innervated by VII CN
Displayed on an oscilloscope connected to an audio amplifier
• Stimulation at the brainstem with a threshold < 0.05mA
predicts good facial nerve outcome

18. Tuning Fork Tests:
• Tuning fork: frequency of 512 Hz.
 Higher frequency tends to decay quickly
 Lower frequency tends to enhance perception
• Rinne Test
• Positive Rinne’s test – AC > BC
• Negative Rinne’s test – BC > AC
(Conductive deafness > 25 dB )
• False Negative Rinne Absent hearing in
the test ear but perceived from the BC
stimulus of the contralateral (non-test)
ear.

19. Weber Test
• The tuning fork is struck and the base placed on
either the forehead, vertex or upper incisor
teeth.
• The patient is asked where the sound is heard
loudest.
Unilateral SN deafness: good ear
Conductive deafness :affected ear.

20. Modified Schwabach Test
• Compares the BC of the patient a normal hearing person.
• The tuning fork is placed on the mastoid with the meatus blocked.
• When the patient no longer hears it, the fork is placed on the normal
hearing person’s mastoid (usually the examiner’s), again with the
meatus blocked.
• If the examiner hears the note, the patient’s BC -->reduced.

21. Pure Tone Audiometry
• Usually frequencies of 250-8000 Hz are used in testing because this
range represents most of the speech spectrum.
• It differentiates between conductive and sensorineural deafness.
• In conductive deafness, the pure tone BC has a normal threshold,
while pure tone AC has elevated thresholds.
• In SNHL, both AC & BC thresholds are elevated.
• Disadvantage:
-purely subjective/cannot be performed in a child/noncooperative and in
unconscious patients.

22. • Normal hearing
• < 20 db HL (adults)
• < 15 db HL (children)
• Mild hearing loss = 20-40 db HL
• Moderate hearing loss = 41-70 dB HL
• Severe hearing loss = 71-90 db HL
• Profound hearing loss = 90+db HL

23. Speech discrimination audiometry:
• It is another phenomenon which is associated
with cochlear damage.
• It is tested by using standardized
monosyllables using a live voice or taped
material.
• Patients with both cochlear and retrocochlear
lesions have low speech discrimination scores
• Retro-cochlear lesions having lower scores
than those with cochlear lesions.

24. Modified Gardner-Robertson system of hearing grade

25. Brainstem Evoked Response Audiometry(BERA)
• Its a brief auditory stimulation given to
the ear which is conducted through the
auditory pathway upto the midbrain.
• First described by Sohmer and
Feinmesser in 1967
• Recorded (differential amplification)
Active electrode-vertex or high forehead
Reference electrodes-mastoids or the ear
lobes.

26. Brainstem Evoked Response Audiometry(BERA)
• Within the first 7 milliseconds following acoustic stimulation, a series
of five negative deflections appear.
• Their sites of origin are thought to be as follows:
N1 cochlear nerve
N2 cochlear nucleus
N3 superior olivary complex
N4 lateral lemniscus
N5 inferior colliculus

27. Brainstem Evoked Response Audiometry
• The normal latency for wave V is between 5 and 5.7 ms.
• The inter wave period between the wave I and wave V may be used to detect a
retrocochlear lesion.
• The maximum interaural latency difference between waves I and V in the normal
population is no more than 2 ms.
• Advantage
• Non-invasive techniques and is
• Easy to record,
• Not strongly affected by attention/sleep/sedation/anaesthesia / age.

28. Electrocochleography(ECoG)
• ECoG is a short latency evoked potential that reflects the summed activity of a large number of peripheral
auditory nerve fibres as well as the response of generators located within the cochlea itself.
• The ECoG consists of three distinct evoked potentials:
1. The cochlear microphonic (CM) Generated ffrom hair cells
2. The summating potential (SP)
3. Compound action potential (AP)
In acoustic neuroma Broadening of the eighth nerve action potential
Adv.
• Direct recording of CNAP from nerve
• Rapid feed back of N1
• Not affected by anesthetic agents
• Almost always detectable
Disadv.
• Impair Surgical field
• 8th CN visible before it can be used
• Dislodgment of electrode
• Fluid in middle ear may block the sound
transmission

29. • Main grading systems for acoustic neuromas. The classifications on the left side (blue area) are mainly based on
tumor size, while those on the right side (green area) are based on the anatomical relationship around the tumor..
Grading and classification of Acoustic Neuroma

30. Koos classification combines the tumor size and anatomical
relationship for larger tumors

31. Management options -
• Surgery
• Radiosurgery or
Fractionated RT
• Observation (with
careful audiologic and
radiologic monitoring

32. Retro-mastoid suboccipital

35. Decision making
Total versus Subtotal Removal
• As a general rule, total removal has to be attempted in all cases of acoustic neuroma
• However, subtotal removal can be preplanned or unplanned.
• STR will lead to eventual recurrence, and revision surgery is more difficult and has a worse outcome
Preplanned Subtotal Removal
• In patients > 70 years of age, a small part of the tumor may be left over the facial nerve
• Impossible to identify the arachnoid plane of cleavage
• Prudent to leave the capsule of tumor attached to the brainstem and/or to the facial nerve.
• This reduces the injury to the nerve, and therefore more likely results in better facial nerve function
postoperatively.
Unplanned Subtotal Removal
• Intraoperative complications, bradycardia during surgery at the brainstem, or other anesthesia-related
complications,
• It is prudent to stop the operation for a few minutes and then restart the dissection.
• However, if these complications are repeated, the operation should be terminated.

36. Intraoperative injury
• Direct trauma or nerve stretching during
surgery
• Mostly Neuropraxia/ axonotmesis
• Devascularisation of nerve segments that are
effaced by large tumors
• Thermal injury(Both hot and cold)
• Caution while using bipolar cautery
• Cold irrigation may “stun” the nerve
• During drilling of IAM irrigation with
warm saline
• Initial debulking f/b dissection
• Dissect the tumour from the nerve
and not vice-versa
• Excessive pressure on facial to be
avoided
• Cottoinoids and micro-suction
devices to be used
• Sharp dissection is a must until clear
plane is identified
• Avoid excessive cerebellar
retraction to avoid undue tension on
the nerve
How to Minimize?

37. Intraoperative complication Avoidance
VII CN Preservation
• Intra-op BAER
• Identify cochlear division at
the transverse crest
• Arachnoid over the cochlear
nerve to be preserved
• Minimal manipulation of the
nerve
• Preservation of auditory
artery
• Protect with gelfoam
VIII CN Preservation
• Intraoperative monitoring
• Identify nerve at the nerve root
exit
zone and at the transverse
crest
• Sharp dissection
• Minimal manipulation of the
nerve
• Debulk large mass-remove
tumor from the nerve, not nerve

39. NF II

40. Intraoperative placement of Cochlear implants

41. Special conditions
Acoustic Neuroma in the Only Hearing Ear
• The introduction of cochlear implants (CIs) and brainstem implants has greatly increased the
treatment options.
• NF2, B/L VS likely have a similar situation of only hearing ear.
• Prefer to wait and watch -regular 6 monthly F/ U gd MRI as well as hearing assessment
• Hearing preservation surgery is always attempted.
• Offer a CI on the contralateral deaf ear, if applicable, before making a decision on the acoustic
neuroma.
• Depending on tumor size, rate of growth, and the patient’s choice, radiosurgery with low-dose
irradiation may be an option.

42. Syndrome of delayed post-operative HL
• Patients who have initial hearing preservation gradually lose hearing in the
post-operative period.
• Exact cause of deterioration-not known.
• Postulated that combination of the effects:
Cerebellar retraction
Disturbances in the microcirculation in the vasa nervorum during mechanical
manipulation of the cochlear nerve
 An increased permeability of the endo-neural vessels after mechanical compression
trauma

43. Rehabilitation of facial nerve
• Complete or partial anatomical loss
• 1) End-to-end anastomosis with biological glue
• 2) Facial-hypoglossal nerve anastomosis
when stumps cannot be located.
• 3) Nerve gapping(>1cm)- Nerve grafting{Great auricular/
Sural Nerve}
• 4) Facial Reanimation surgery
• Cross facial nerve grafting
• Musculofascial transposition

45. Recent Advances
• Direct recording of potentials from
cochlear nucleus in lateral Recess.
• Fast BAER response (10 sec)
• By using electrodes attached to
cerebellar retractor.
Intraoperative Fast BAER

46. Major Principle of Surgery
1. Important neural structures, should be identified as early as possible during surgery,
which enables their preservation and guides subsequent operative steps
2. The tumor should be initially debulked
3. The dissection from the surrounding structures should be performed
4. The dissection should always be performed in the arachnoid plane
5. Bipolar coagulation, especially in the vicinity of a cranial nerve, should be avoided.
6. Most preferred approach is the Retro-sigmoid approach.
(safe, relatively simple, and provides a panoramic view of CPA and low procedure-related morbidity rate)

47. Conclusion
• Acoustic Neuromas are benign, complete removal leads to excellent long-term
outcomes. (exception in the only hearing ear)
• Comprehensive Anatomical knowledge, good Microsurgical technique,
maintenance of the operative plane is a prerequisite for achieving good surgical
results.
• Use of IONM- a valuable adjunct for acoustic neuroma surgeries
• Post operative complication and Rehabilitation should be dealt with aggressively
• Goal of surgery- changed from prolongation of life to Function preservation

48. THANK YOU
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