a

Left-sided retrosigmoid craniotomy for the resection of a vestibular schwannoma

this is Jacques Marcus presenting

surgical video of a left right or

sigmoid craniotomy for the resection of

a vestibular schwannoma I would like to

thank Peter amantha my current fellow

who was a co surgeon on the case and who

helped edit this video I will present

the preoperative imaging the patient

presentation as well as the steps of the

surgical approach and then the

post-operative imaging the patient is a

51 year old female with approximately

one year of dizziness as well as six

months of progressive left-sided hearing

loss she presented to an ENT surgeon who

performed an audiogram revealed 75%

speech discrimination and mild the

hearing loss at 35 decibels

she had mild left facial numbness

otherwise was neurologically intact the

MRI reveals two by two point five

centimeter Levis tabular schwannoma here

is the tracing of her audiogram with the

results described before

here is the patient seen immediately

preoperatively with a normal face her

preoperative imaging reveals on t two

sequences of the MRI the typical

acoustic neuroma findings with six

millimeter of IAC involvement and here

is a contrast enhancement showing

similar findings including distortion of

the fourth ventricle an involvement of

six millimeter of the internal auditory

canal and usual enhancement the left

right or sigmoid craniotomy was planned

regarding the positioning first the

patient has facial nerve and auditory

electrodes placed in in the usual manner

and then she will be placed in the

lateral position with the left side up

her head is getting fixated in the

mayfield head order the patient is

placed in the right lateral decubitus

position and the right arm is carefully

cocooned in form to avoid any pressure

points on it the right axillary roll is

placed under the right axilla next the

surface marking over the grotto

me is done this is a point that is about

four centimeter behind the external ear

canal and now we are marking the mastoid

tip and then we are tracing the

estimated position of the transverse

sigmoid sinus then we mark the contour

of the planned bony craniotomy to

correspond to that location just under

the transverse sigmoid Junction and

finally the skin incision is placed and

it is usually C shaped and encompassing

the bony craniotomy

a green beret tractor system is placed

to apply the fish hooks on for the soft

tissue exposure the skin incision is

made Bovie cautery will be used as well

as bipolar cautery for hemostasis it is

important to lift the cutaneous flap

over the epimysium of the muscle rather

than to take Maya cutaneous flap all in

one piece this will give greater freedom

of exposure and more shallow exposure

bringing the surgeon closer to the

pathology fishhooks are applied

strategically to again eliminate the

depth of the exposure and to flatten it

the t incision is made into the superior

nuchal line emissary venous bleeding is

controlled with bone wax after the

horizontal portion of the T is made the

vertical portion of the T is a completed

branch of the occipital artery is

encountered and coagulated it is

important to keep that muscular incision

as short as possible and then to go

subperiosteal e to expose the bone and

to apply the fishhooks in a manner that

maximizes bony exposure we then mark a

point four centimeter posterior to the

external eteri canal corresponding with

the

initial marking we had placed on the

skin and this will be the site of

initial drilling here is a surgical

setup a large cutting bird is used to

initiate the craniotomy this is similar

to the neurological school of drilling

and then a diamond is utilized as we get

nearer the inner table of the bone when

dura or venous sinus is encountered care

must be taken to remove the eggshell of

bone that is encountered then we strip

the dura with a dental instrument to

allow the footplate of the drill to

elevate a free bone flap it is important

to take care of not entering the venous

sinuses of course and not to allow the

footplate to tear the dura the sequence

of events is important to avoid

excessive bone loss that's why we

perform the craniotomy after the small

craniectomy the diamond is used to drill

flush the inner table of the remaining

bony edges here is a transverse sigmoid

turn evident with a bluish discoloration

and that should signal the end of the

bony resection the first dural incision

that needs to be made is near cisterna

magna this is very important

particularly in larger tumors to obtain

CSF relaxation with that small

transverse incision made traction suture

is placed to free up the surgeons second

hand and the dural opening is enlarged

and under the microscope the latter

recess of the cisterna magna is obtained

and

CSF is drained from it the dural flap is

C shape and based medially to avoid a

contraction of the dura after the end of

the case next under the microscope will

identify the tumor in the

cerebellopontine angle the dissection

always starts at the Codel end of the

exposure near the lower cranial nerves

here significantly sized inferior

petrosal vein is seen coursing just

above the reutlitz of the ninth and

tenth nerves the medulla is seen at the

distance sharp dissection is used to

separate the cerebellum from the Lordran

nerve and the vein until the lower pole

of the tumor is seen here is a fascia

here is a facial nerve stimulator being

used to scout for any facial nerve

fibers on the dorsum of the tumor

none were identified which allowed us to

proceed with the usual debulking of the

tumor from posteriorly this is usually

done with scissors and suction but

sometimes also with caviar on ultrasonic

aspirators in this particular case we

did not have the need to use an ax

cavity on ultrasonic aspirator and

therefore we used the usual technique of

separating the tumor of the brain stem

after central debulking this is best

done with these micro forceps and

suction lifting the inner medial capsule

of the tumor of the brainstem and as we

near the brainstem use the facial nerve

stimulator to identify the facial nerve

and here is the facial nerve seen at its

exit zone next we surrounded the humor

from superiorly

we placed a nonstick telfa between the

tumor capsule and the cerebellum and the

brain stem and here is the superior

petrosal vein lifted off the tumor and

at a deeper level the superior

cerebellar artery and the trigeminal

nerve are seen preserved and mobilized

away we stimulated the capsule of the

tumor again looking for the facial nerve

and in the absence of facial nerve

fibers we proceeded to remove another

large piece of the tumor with micro

scissors more debulking is done until we

had a much clearer view of the facial

nerve at its exit from the brainstem and

here is a facial nerve stimulator

indicating its course now it is time to

drill the internal auditory canal we

like very much the use of the long

curved drills that have protective

sleeve around the shaft this would allow

us to focus on the tip of the drill and

not worry about grabbing any important

structures along the course of the shaft

the drilling of the internal auditory

canal is done in again in an eggshell

technique when the internal auditory

contents are identified the eggshell is

broken with angled micro curettes

or round knives and the bone is sculpted

in the direction of the internal

auditory canal nerve hook or a crabtree

instrument is used to feel along the

internal auditory canal then the dura

along the internal auditory canal is

open and care is being taken to isolate

the cochlear nerve at the inferior edge

the tip of the tumor in the IAC is

identified and rolled medially carefully

it is important not to apply undue

tension as to not to as to not tear the

cochlear fibers of the cribriform plate

of the lateral end of the IAC here is a

cochlear nerve well seen sharp

meticulous dissection continues from

laterally to immediately using the plane

between the arachnoid layers and then

this dissection plane will meet the

dissection plane that had been started

previously from medially to laterally

this is now the final attachment of the

tumor and it is important to lift it off

the seventh and eighth seventh nerve and

cochlear nerve and transect any remnants

of vestibular fibers and arachnoid

holding it to it and preserving blood

supply the seventh nerve and eighth

nerve are clearly preserved anatomically

as well as functionally because the

brainstem auditory potentials did not

change during the case after inspecting

the internal auditory canal the closure

begins first we have to make sure that

our cells were not encountered and we

can use either an endoscope which was

not used in this particular case or a

nerve hook to explore for air cells and

we found a small air cell in a superior

wall of the internal auditory canal we

placed some bone wax into it and then a

Sergi cell to reinforce the bone wax and

on top of this we will place a piece of

the origin as a dural substitute on top

of the internal auditory canal without

over packing the entire case was done of

course without any self-retaining

retractor

since positioning allows the cerebellum

to fall away from the tumor

dural closure is meticulous and in

usually running for owner alone stitch

we then wax any mastoid air cells

thoroughly and then augment the dural

closure with more durjan dural

substitute and then replace the bone

flap with three plates and screws over

the defect and then close the muscle the

Galea with absorbers which are running

locked 3 or prolene to the skin here is

a tracing of the baseline and final

brainstem evoked potential showing no

change at all during the case

post-operative imaging at post-op day 2

shows complete tumor resection as seen

on this GAD images axial and coronal a

physical examination of the patient is

conducted on post-operative day 2

raise your eyebrows like this close your

eyes tight good perfect thank you follow

my finger to the right to the left very

good big smile again here is the patient

at six weeks post-op with a well-heeled

scarred an excellent facial nerve

function an audiogram was repeated at

six weeks revealing very good

preservation of hearing particularly in

the lower frequencies