Azam Basheer MDHenry Ford Neurosurgery

Introduction

- Posterior circulation aneurysm ~10-15% of all aneurysms (basilar apex > SCA > PICA)

- First surgical clipping described by Gillingham in 1958 and Drake in 1961

- Both surgeons used a subtemporal approach with modest success

Arises from the confluence of the two VA's at the pontomedullary junction

Ascends in the central gutter (sulcus basilaris)

Divides into PCA's and SCA's just inferior to the pituitary stalk.

BA Anatomy

Thalamoperforators

Perforator Origins: basilar trunk, proximal P1, P-comm

Oculomotor nerve passes between PCA and SCA

Interpeduncular Fossa

Interpeduncular Fossa Boundaries

- Anterior: clivus and posterior clinoid processes

- Lateral: mesial aspects of the temporal lobes and tentorial edges

- Posterior: the cerebral peduncles

- Superior: mamillary bodies and posterior perforated

substance

Relative indications for surgery

1. Unfavorable coiling anatomy

2. Thick cistern clot?

3. Symptoms attributable to brainstem compression (Giant aneurysms)

Choosing the Right Surgery

① obtain the shortest trajectory to the lesion

② Adequate bone removal for minimal brain retraction

③ Skeletonization & protection of CN and vascular structure

selection of surgical approach based on location

Site of Aneurysm Skull base Approach

Vertebral artery Far-lateral

Low Basilar Far-lateral

Midbasilar artery Petrosal,Subtemporal?

High basilar artery Pterional +/- OZ transyslvian

Subtemporal

Basilar Apex

Two pure approaches

1. Trans-sylvian approach +/- Modifcations

2. Subtemporal approach

Subtemporal Approach

Trans-Sylvian Approach

Trans-sylvian + OZ approach

More Superio-medial

Trans-sylvian Approach

Trans-sylvian approach

Assets Liabilities

• familiar

• prox. control

• exposure of both P1

• wide exposure

• Less temp. lobe

retraction than subtemporal

approach

• “Low” bifurcation BA

• Poor visualization of

peroforators

• ant. or post. directed

aneurysm

Trans-sylvian approach

“low” bifurcation

Excellent visualization for aneurysms necks at the level between the midsellar depth and a line 1 cm superior

Surgical Technique

supine with head turned 45 degrees and slightly extended

Positioning is Key

Malar eminence

zygomatic root 1cm ant to tragus, behind hair line towards midline

Incision

Keyhole, above the zygoma, along the posterior temporal line, midfrontal

Temporalis muscle retracted down

Craniotomy

Sphenoid ridge resection

Ant. and Post. Clinoid Processes Resection

Cutting arachnoid adhesions along

the middle fossa floor frees the

inferior temp lobe

Opening the Dura and Splitting The Fissure

Divide the temporopolar vein to untether the anterior temporal lobe

EVD placed intraoperatively

Paine's point

Open the cisterns

Anatomic triangles

providing access to the

basilar bifurcation:

1 optic-carotid triangle

2 carotid-oculomotor triangle

3 supracarotid triangle

The carotid-oculomotor

triangle is the one used most

commonly for basilar bifurcation

aneurysms.

Identify the Pcomm and CN III

Open the membrane of Liliequist along CN III

Liliequist’s membrane

CN III

PComm

Forms a “curtain” for the interpeduncular cistern and the roof of the prepontine

cistern

Stay on inf. surf. of Pcomm to avoid injury to the

thalamoperforaters

Follow Pcomm to P1-P2 junction

+/- Sacrficing the PComm

Ensure Thalamoperforaters are free

SUMMARY

Sylvian dissection: freeing of the frontal and temporal lobe

Open the cisterns

Open the membrane of Liliequist along CN III

Dissect along the Pcomm until P1 is seen and then follow to BA

Subtemporal Approach

Subtemporal approach

transsylvian app.

- below the middle depth of the

sella turcica

- posterior projection

- allows to dissect the perforators

of the posterior wall of aneurysm

- large aneurysm

right-sided approach : left III nerve palsy, right hemiparesis

left-side approach

Subtemporal approach

Assest Liabilities

• prox. control

• dissection of perforators

• tentorial division widens exposure

• Good visualization of clip

• ant. or post. directed

aneurysm

• narrow field

• contralat. P1 control

• temporal lobe injury

• CN III palsy

• bleeding control

Skin incision

Craniotomy

Biting off temporal bone

Dural opening

Lifting up temporal lobe

Stitching up tentorium

Vs. Cutting the tentorium

Releasing arachnoid adhesions

Checking for perforators

Clip application

Clip application