Surgical Approaches to Intracranial Aneurysms Chapter 383

BASIC TENETS OF CEREBROVASCULAR SURGERY Pathologic brain condition (swelling or young brain hemorrhage) fullness of the brain The major intracranial arteries reside in the subarachnoid space dissection of the subarachnoid space are fundamental in cerebrovascular surgery Difficult dissection:presence of hemorrhagic byproducts, inflammatory reactions,fibrinous adhesions, and, occasionally edema

treat hydrocephalus before the craniotomy ventriculostomy on the opposite side of the craniotomy Release of CSF—dissection of various CSF cisterns or drainage through CSF diversion brain relaxation From the pterional approach, the sylvian, carotid, lamina terminalis, interpeduncular cisterns often allow drainage of a large volume of CSF

Far lateral approach: CSF release from the Post and lat cerebellomedullary cisterns In the interhemispheric approach:lumbar drainage Intravenous hypertonic solutions or pharmacologic metabolic suppressive agents (e.g., thiopental or propofol) Head elevation and adequate cervical venous drainage, and hyperventilating the patient Removal of enough bone particularly deep seated-aneurysms, such as aneurysms of the basilar tip, low-lying aneurysms of the p com A, and A com A.

Proximal and Distal Control Prevent devastating hemorrhage in the event of intraoperative rupture Aiding in perianeurysmal dissection and eventual clip placement At anterior circulation, proximal and distal control may be accomplished with temporary clip

In some cases:proximal control of the parent vessel may be impractical Alternative techniques: aneurysms of the proximal intracranial internal carotid artery (ICA) proximal control in cervical ICA in the neck Even if the cervical ICA is not exposed preoperatively proximal control may be achieved through manual compression of the cervical ICA

If proximal control cannot be secured intracranially or extracranially ( some aneurysms of proximal basilar artery) adenosine-induced bradycardia and hypotension

COMMON SURGICAL APPROACHES TO INTRACRANIAL ANEURYSMS Pterional (Frontotemporal) Craniotomy Orbitozygomatic Craniotomy Anterior Interhemispheric Craniotomy Subtemporal Craniotomy Far Lateral Craniotomy Transpetrous Approach

Pterional (Frontotemporal) Craniotomy Anterior fossa intradural craniotomy approach Most aneurysms of the ant. Circulation: intracranial ICA Middle cerebral artery Posterior communicating artery Most AComA aneurysms

Positioning Supine with a shoulder roll under the ipsilateral shoulder. The head is placed in three-point pin fixation Rotated 10 to 45 degrees to the contralateral side translated anteriorly. The vertex is then rotated 10 to 20 degrees toward the floor Malar eminence at the highest point

Skin and Soft Tissue Dissection Curvilinear in shape beginning 0.5 to 1 cm anterior to the tragus No more than 1.5 cm inferior to the zygoma (to avoid injury to the frontal branch of the facial nerve) Extending superiorly and anteriorly, crossing the midline Ending at or immediately posterior to the hairline.

Avoiding to the injury to the superficial temporal artery or violation of the temporalis fascia temporalis muscle may be incised, mobilized, and retracted by numerous techniques Myocutaneous Flap Submuscular Dissection Subfascial Dissection Interfascial Dissection

Craniotomy and Bone Dissection three bur holes are made: one just above the root of the zygoma one above the superior temporal line the other in the keyhole The craniotomy itself proceeds with C-shaped cuts bounded

Pterional craniotomy for approach to aneurysms of the middle cerebral artery

Anterior fossa intradural craniotomy for approach to aneurysms in the middle cerebral artery

The only difference between a pure pterional craniotomy and the anterior fossa intradural craniotomy is the amount of bone: the anterior fossa intradural craniotomy provides more of a skull base approach craniotomy extending along the orbital roof to just medial to the supra orbital notch preventing brain retraction provides better circumferential exposure of the aneurysm

At the anterior fossa intradural Craniotomy: drill the sphenoid ridge the lateral aspect of the superior orbital fissure, and the orbital walls may be drilled down Further extradural bone work removal of the anterior clinoid process (as for some proximal ICA aneurysms) or the optic strut, or both. dural tack-up sutures may be placed before the dura is opened.

Dural Opening and Intracranial Dissection The dura is opened in a C-shaped manner reflected anteriorly tacked up snugly with dural sutures against the remnants of the sphenoid ridge The frontal lobe is then retracted slightly carotid, chiasmatic, and lamina terminalis cisterns are incised to release CSF Occasionaly lumbar drain preoperatively contralateral basal cisterns and lamina terminalis

Dissection of the sylvian fissure with the opening of the sylvian cistern arachnoid Aneurysms of the MCA reside in the sylvian cistern and may be identified relatively early in the process of sylvian fissure dissection. more dissection of the carotid cistern (for aneurysms of the ophthalmic artery and of the posterior communicating artery) the lamina terminalis cistern dissection (aneurysms of the AComA)

Orbitozygomatic Craniotomy a variation on the traditional pterional craniotomy improved exposure to, and maneuverability around: orbital apex, basilar apex, paraclinoid and parasellar regions the cavernous sinus, the upper third of the clivus floor of the anterior and middle cranial fossae.

For aneurysms of the basilar apex and giant or otherwise complex aneurysms of the anterior circulation The removal of the orbitozygomatic complex is the only difference between the orbitozygomatic approach and the anterior fossa intradural craniotomy “deeper”skull base approach high-riding aneurysms of the basilar tip and large posterior-pointing aneurysms of the AComA

Positioning Identical to that described for the pterional craniotomy but greater degree of contralateral head rotation (30-60 degrees

Skin and Soft Tissue Dissection Similar to pterional craniotomy, with several minor exceptions. Vascularized pericranial graft Subfascial dissection of the temporalis muscle and fascia The periorbital fascia is dissected free of the lateral orbital wall and superior orbital roof, toward the orbital apex

Craniotomy and Bone Dissection Various methods have been proposed : Removal of the orbitozygomatic unit as one piece along with the cranial flap Removal of the orbitozygomatic unit independently of the cranial flap Removal of a modified fronto-orbital unit alone without the zygoma. The “two-piece” orbitozygomatic approach is commonly preferred

Orbitozygomatic approach for aneurysms in the basilar trunk and posterior cerebral artery

Dural Opening and Intracranial Dissection dura is opened in a C-shaped manner with the apex of the dural incision at the posterior aspect of the craniotomy. the dural flap is centered over the orbit rather than the pterion dural tacking sutures are used to gently depress the globe and periorbita out of the operative corridor.

Anterior Interhemispheric Craniotomy Aneurysms of the pericallosal artery (PcaA) These aneurysms lie in the midline, deep to the falx, in the interhemispheric fissure, just superior to the corpus callosum. Right side of the falx is frequently preferred Less frequently : aneurysms of the AComA and specifically in aneurysms for which a combined A2-A2 segment bypass or in those that point posteriorly and superiorly.

Positioning Depending on the location of the PcaA aneurysm. For both proximal and distal PcaA aneurysms, the patient is placed supine head is often in a neutral position with the neck slightly extended for proximal PcaA aneurysms (those originating from the A3 segment) head is typically turned 90 degrees to the right (with a large roll under the left shoulder) for aneurysms of the distal PcaA (A4 or A5 segments).

Skin and Soft Tissue Dissection A right-biased bicoronal incision For aneurysms of the distal PcaA, a horseshoe incision may be preferable. This should be situated two-thirds anterior and one-third posterior to the coronal suture Anterior aspect of the incision just behind the hairline Medial aspect of the incision just crossing the midline.

Craniotomy and Bone Dissection craniotomy is often rectangular posteriorly to the coronal suture anteriorly to the inferiormost aspect of the frontal bone visible (to allow for proximal control in proximal PcaA aneurysms) laterally to the superior temporal line and medially just across the superior sagittal sinus . The inner table of frontal bone may be drilled. obtaining proximal control in very proximal PcaA aneurysms.

Interhemispheric approach for aneurysms in the pericallosal and callosomarginal arteries

Dural Opening and Intracranial Dissection The dura is opened in a semicircular manner and flapped toward the superior sagittal sinus Preserve bridging veins, particularly those that are large and situated posteriorly.. A 3-cm gap between bridging veins is frequently found dissection. Dissection is then carried down in the interhemispheric fissure, deep to the falx, until both PcaAs are reached

The majority of PcaA aneurysms are located 1 to 2 cm anterior to the section of PcaA Thus dissection is carried anteriorly along the artery until the aneurysm is visualized. For aneurysms of the AComA,craniotomy is based more inferiorly, just above the frontal sinus and the interhemispheric dissection Direct access to the A2 segment and the anterior communicating complex.

Subtemporal Craniotomy For aneurysms of the peripeduncular segments of the posterior cerebral artery (the P2 segment) superior cerebellar artery aneurysm as well as giant, complex, posteriorly projecting or low-lying aneurysms of the basilar artery

Positioning The park bench position The dependent arm is held off the table in a padded sling. head is positioned with the sagittal sinus parallel to the floor the vertex rotated slightly toward the floor. A right-sided approach is often preferred

Skin and Soft Tissue Dissection The skin incision is linear and perpendicular to the zygoma frontotemporal or posterior temporal flap The incision begins 1 cm anterior to the tragus and is carried to the lower border of the zygomatic arch. The muscle and fascia are then removed from their zygomatic arch attachments posteriorly Avoid injury to the facial nerve.

Craniotomy and Bone Dissection 4 × 4 cm craniectomy. For aneurysms of a high-riding bifurcation of the basilar artery partial resection of the zygomatic arch improve visibility of the interpeduncular cistern lessen the need for temporal lobe retraction.

Temporal craniotomy for approach to aneurysms in the basilar tip.

Dural Opening and Intracranial Dissection The dura is often opened in a C-shaped manner and reflected inferiorly Dissection proceeds beneath the temporal lobe in a direction almost perpendicular to the sagittal plane. slight rotation of the patient’s vertex toward the floor effective brain relaxation (lumbar drain)

visualization of the interpeduncular cistern and ambient cistern contents partial resection of the parahippocampal gyrus (which may obscure the upper 33%-50% of the ambient cistern) visualization of the posterior aspect of the ambient cistern is occasionally limited by the vein of Labbé alternative surgical

Modifications partial tentorial section. retract the tentorial edge by suturing it to the dura of the middle cranial fossa. Particularly low-lying aneurysms of the basilar artery: located between the vertebrobasilar junction origin of the anterior inferior cerebellar artery combined infratentorial/supratentorial approach (addition of a small, lateral suboccipital craniotomy)

Far Lateral Craniotomy proximal to the superior cerebellar arteries otherwise Lateral suboccipital approach Extreme lateral approach Extreme lateral inferior Transcondylar exposure Bone is removed laterally, just medial to the mastoid area corridor is created along the medial aspect of the petrous bone visualization of the vertebral and basilar trunks without undue retraction on the cerebellum.

Positioning sitting position Risk of venous air embolism three-quarter prone or modified park bench position Minimizing brachial plexus compression and greater venous return in comparison with the full prone position.

Patient positioned in park bench position for the far lateral approach

Skin and Soft Tissue Dissection An upside-down hockey stick incision Beginning in the midline over the midcervical spine ,extending superiorly past the inion laterally, parallel to the superior nuchal line Inferiorly, terminating at the mastoid tip. occipital artery preserved

Craniotomy and Bone Dissection C1 laminotomy(For higher riding aneurysms, this procedure may not be necessary.) A suboccipital craniotomy is then performed. The craniotomy itself should stretch from the midline foramen magnum Superiorly to the superior nuchal line and transverse sinus laterally to the asterion and the underlying transversesigmoid junction Return inferiorly to the lateral aspect of the foramen magnum.

Far lateral transcondylar approach to aneurysms in the vertebral artery

Dural Opening and Intracranial Dissection The dural opening begins in the cervical midline beneath C1 courses superiorly and then laterally, terminating at the superolateralmost aspect of the craniotomy. The inferiormost aspect be extended laterally and inferior to C1 Visualization of vertebral and basilar artery trunks and their associated branches. CSF drainage from cerebellomedullary cistern. Alternatively, lumbar drain

Transpetrous Approach Aneurysms of the basilar trunk are at higher risk for rupture Transpetrous approach, known as the transpetrosal or combined supra-infratentorial approach Basilar artery, the anterior portion of the brainstem, and the cerebellopontine angle. This approach includes: intradural subtemporal craniotomy, a presigmoid craniotomy,and an added posterior fossa craniotomy.

Positioning Lateral position. Shoulder roll Head turned to the contralateral and completely horizontal. Tilting the head slightly towards the floor allows greater exposure Assessed preoperatively to ensure that the cervical spine can tolerate this positioning. The head is secured in three-point fixation with Mayfield tongs.

Skin and Soft Tissue Dissection An extended horseshoe incision is made starting about 1 cm anterior to the tragus along the zygoma extending superiorly to just past the superior temporal line, curving posteriorly to just past the mastoid process then curving inferiorly to several centimeters below the mastoid process The skin flap is reflected anteroinferiorly The temporalis muscle and fascia are then incised Preserved the superficial temporal artery.

Craniotomy and Bone Dissection A temporo-occipital bone flap A mastoidectomy and skeletonization of the sigmoid sinus to the jugular bulb exposes the sinodural angle and presigmoid dura. If the lesion is low, extradural to drill off the petrous apex. The subtemporal dura is then dissected The middle meningeal artery is cut at the foramen spinosum

greater superficial petrosal nerve is dissected in a posterior-to-anterior direction to avoid injury to the facial nerve. Drilling of the horizontal portion of the petrous carotid artery. The third branch of the trigeminal nerve and the gasserian ganglion are dissected The petrous apex can then be drilled

Transpetrosal approach

Dural Opening and Intracranial Dissection The dura is then opened at the temporal convexity and presigmoid dura intradural and middle fossa approach to the basilar trunk The superior petrosal sinus is ligated The tentorium is incised then the presigmoid dura is incised toward the clivus. This exposes the anterolateral portion of the pons.