Microsurgery of Vertebral Artery, Posterior Inferior Cerebellar Artery, and Vertebrobasilar Junction Aneurysms

Eric C. Chang n Brian L. Hoh n Christopher S. Ogilvy9/02/16

Clinical significance• Uncommon• High risk for rebleeding • High morbidity and mortality rates• Region of the skull base that can be difficult to

access surgically• Close proximity to the brainstem and lower

cranial nerves• High incidence of fusiform nonsaccular aneurysms• Dissecting aneurysm

Indications• Ruptured vertebral artery and vertebrobasilar

junction aneurysms cannot be left untreated• Timing– The International Cooperative Study on the Timing of

Aneurysm Surgery did not include enough vertebrobasilar aneurysm to make any significant conclusions about the timing of surgery for aneurysm at this location

Presentation• SAH• Ischemic symptom• Unruptured– signs and symptoms of ischemia or mass effect– cranial nerve deficits(V to XII) : dysarthria,dysphagia– brainstem compression– cerebellar symptom : ataxia– hemiparesis– posterior fossa symptoms

Diagnostic evaluation• first clinically, by history and examination• computed tomography (CT)– Hydrocephalus 95%– IVH 95%– Supratentorial SAH 70%– Isolated posterior fossa SAH 30%

• lumbar puncture

Diagnostic evaluation• Vertebral dissection– string sign– pearl and string sign– tapered narrowing– occlusion– double lumen– pseudoaneurysm

• 4-vessel angiogram : gold standard

Preoperative evaluation• Orientation and projection of the neck and dome– The neck is encountered before the dome

• Size– Giant : not amenable to standard surgical clipping– CTA or magnetic resonance angiography– Varying – Degrees of intraluminal thrombosis– The angiographic opacity may not show the full size of the

aneurysm appreciated on CT scan

Preoperative evaluation• Angiographic detail– PICA reduplicate– PICA contralateral artery is present– PICA territory is supplied by an alternative vessel : AICA– PICA are being supplied through the posterior circulation• Fetal type PCoA• Size of PCoA : small worse outcome

– Bony structure• bony anatomy of the posterior fossa

Technique

tonsillomedullary segment

distal to the cerebellotonsillar and cortical segments

vertebral arteryproximal segment PICA, vertebrobasilar junction aneurysms

midline vertebrobasilar junction aneurysms

unusually high vertebrobasilar junction aneurysms

Far-Lateral Suboccipital Approach(Heroes)vertebral arteryproximal segment PICAvertebrobasilar junction aneurysms

Transfacial Transclival Approach(deFries and colleagues)

midline vertebrobasilar junction aneurysms

Transfacial Transclival Approach(deFries and colleagues)• Supine position• Lumbar drain or ventriculostomy• Doppler probe : preserve the facial artery• Incision : the glabella around the right lateral alar

margin to the piriform aperture• Osteotomy of the nasal bones and disarticulation of

the septal cartilage from the ethmoid allow for reflection of the nose laterally

Transfacial Transclival Approach(deFries and colleagues)• The medial wall of one or both maxillary sinuses,

the bony septum, the turbinates, the ethmoid air cells, and the floor of the sphenoid sinuses should be removed

• A large triangular exposure of the clivus is revealed by a midline incision into the retropharyngeal mucosa

• A rectangular window of about 2 cm superior-inferior by 1.2 to 2.5 cm left-right is draggled into the anterior clivus

Combined Subtemporal-Presigmoid Transtentorial Approach

Combined Subtemporal-Presigmoid Transtentorial Approach

• unusually high vertebrobasilar junction aneurysms• lateral position with the ipsilateral shoulder retracted• U shape incision : – anterior to the tragus at the level of the zygoma, circling

above the pinna and descending behind the pinna to a point about 1.5 to 2 cm behind (medial to) the mastoid

• temporal-suboccipital (retrosigmoid) craniectomy

Combined Subtemporal-Presigmoid Transtentorial Approach

• complete mastoidectomy – extensive removal of the posterior-superior petrous

pyramid anteriorly to– but not exposing, the facial canal and the lateral and

posterior semicircular canals• Linear dura incision– parallel to the floor of the middle fossa anteriorly and

to the transverse sinus posteriorly• Vertical dural incision– is made to the presigmoid region continuing up toward the

tentorium

Combined Lateral and Medial Suboccipital Approach• tonsillomedullary segment• The patient position, skin incision, and craniectomy

are as described for the far-lateral suboccipital approach

• bone removal extending well past midline in the inferior aspect of the occipital bone and the foramen magnum as well as the arch of C1

• retract the tonsils upward, medially, or laterally

Midline Suboccipital Approach• the segments distal to the tonsillomedullary segment• standard midline suboccipital craniectomy extending

through the foramen magnum

Treatment of Vertebral Dissecting and Fusiform Aneurysms

• Particularly ruptured ones, carry a high risk for rebleeding in the acute period after the initial bleed and require early management

• If their shape and morphology are such that direct surgical clipping is possible– far-lateral suboccipital approach

• Fusiform morphology– proximal parent artery occlusion (hunterian ligation)– trapping procedures– clip reconstructions

Treatment of Vertebral Dissecting and Fusiform Aneurysms

• Endovascular options– parent vessel occlusion or stent placement– combinations of coil and stent therapies

• In which the ipsilateral vertebral artery proximal to the aneurysm is occluded– adequate retrograde or collateral flow would supply the

cerebellar territories if flow to the ipsilateral PICA is compromised

– If needed, a bypass procedure can be done : occipital-PICA, PICA-PICA bypass

Treatment of Vertebral Dissecting and Fusiform Aneurysms

Complications• injury to the lower cranial nerves (9th through 12th)– standard approaches use a surgical corridor through the

lower cranial nerve rootlets– variable and often tortuous course of PICA and vertebral

vessels occasionally requires retraction of nerve rootlets.– dysphagia, dysarthria, dysphonia, and inadequate

airway protection• the 6th cranial nerve is located close to a high

vertebrobasilar junction and can be subject to injury

Complications• Postoperative lateral medullary (Wallenberg’s)

syndrome if the PICA is occluded

Complications• Transclival approach– Cerebrospinal fluid leak– Meningiits