368 ACoA aneurysm

Anterior Communicating Artery Aneurysms

Youmans,Neurological Surgery 6th chapter 368Judy Huang and V. Germanwala n Rafael J. Tamargo

26/01/59

Vascular anatomy

Vascular anatomy• A1 Segment

– Diameter : 0.9 - 4 mm., average 2.6 mm.– Hypoplasia : <1.5 mm.– 50%, difference in 0.5 mm. between them– 85%, in the presence of an ACoA aneurysm

• Anterior Communicating Artery– Diameter : about half of A1 segment, average 1.5 mm.

Vascular anatomy• A2 Segment(pericallosal a.)

• Perforators of the A1 Segment, Anterior Communicating Artery, and A2 Segment– A1 : medial lenticulostriate a.,2-15 perforator

• supply the globus pallidus and medial portion of the putamen– M1 : lateral lenticulostriate a.

• supply the lateral portion of the putamen and external capsule

– ACoA perforator

Vascular anatomy• Medial Striate Artery (Recurrent Artery of Heubner)

– Most important perforator from the proximal A2 segment– A2 78%,A1 14%,ACoA 8%,Absent 2%– Course : anterior to A1 60%,superior to the A1 40%– Diameter : twice of A1, 23.4 mm.– Supply :

• anterior striatum (caudate nucleus and putamen)• a portion of the outer segment of the globus pallidus• the anterior limb of the internal capsule

Vascular anatomy• Medial Striate Artery (Recurrent Artery of

Heubner)– Injury

• moderate paresis of the contralateral upper extremity

• mild paresis of the contralateral face• dysfunction of the tongue and palate• If the dominant hemisphere is involved an

expressive aphasia

Vascular anatomy• Orbitofrontal artery differ from medial Striate

artery• 5 mm from AcoA• Diameter 0.9 mm. • Course perpendicularly over the gyrus rectus

and across the olfactory tract• Boundary of lamina terminalis cistern

Arachnoid Cisterns

Inferiorly : over the surface of the optic chiasmPosteriorly and Laterally : lamina terminalisSuperiorly : rostrum of the corpus callosumAnterior : A1-ACoA-A2 complex

Arachnoid Cisterns• Carotid cistern

– A1 segment originates within– Supraclinoid ICA

• Chiasmatic cistern– Optic nerves, optic chiasm, and infundibulum– Not contain any major arteries

• Lamina terminalis cistern– Paired A1 and proximal A2 segments,ACoA– Medial striate arteries of Heubner

Most ACoA aneurysms (71.2%) project into the interhemispheric fissureMinority (12.8%) project inferiorly into the chiasmatic cistern16% of all ACoA aneurysms have complex, multilobulated projections)

found entirely within the interhemispheric fissure

partially inside the interhemispheric fissure

adherent to the optic chiasm, the optic nerves, or the dura of the interoptic space

Radiographic Presentation of ACoA Aneurysms

• CT– SAH

• only in the interhemispheric fissure• thicker clot in the interhemispheric fissure

– Intraparenchymal hemorrhage in the region of the gyrus rectus

• Angiography– The highest false-negative rate of angiography of

any intracranial aneurysm– Probably the balanced flow into the ACoA from

the paired A1 segments, which may prevent filling of the aneurysm by the dye

Operative Technique for ACoA and Proximal ACA Aneurysms

• Three anatomic features– their bilateral anterograde arterial supply– their deep,midline location– their intimate relationship to 11 critical arteries

• Pair A1• Pair A2• 2 medial striate a of Heurner• 2 orbitofrontal a.• 2 frontopolar a.• ACoA


• Choice of the Side of the Craniotomy– side of the dominant A1 segment : no significant

benefit in terms of proximal control, but it is advantageous in the sense that the aneurysm neck is exposed before its dome

– right (nondominant) craniotomy

• Head Position– rotated 15 to 45 degrees away from the

operative site– malar or zygomatic eminence the highest point


• Incision• Dissection of the Temporalis Muscle• Frontosphenotemporal (Pterional) Craniotomy


• Drilling the Greater and Lesser Sphenoid Wings• Dural Opening• Sylvian Fissure Dissection

– 6 cm long divided into three 2-cm portions, or thirds– It is best to enter the fissure in its middle third– M2 branch,seen first

• Exposure of the Optic Nerve and ICA– chiasmatic cistern, carotid cistern


• Exposure of the Ipsilateral and Contralateral A1 Segments– Reaching the ipsilateral A1 segment : proximal

control– Dissected distally off the inferior surface of the frontal

lobe– The midpoint of the A1 segment is therefore a good

place for a temporary clip– The contralateral A1 segment is exposed



• Gyrus Rectus Resection– for adequate exposure of most ACoA aneurysms– retractor is repositioned over the medial orbital gyrus

just lateral to the olfactory nerve– medial and parallel to the olfactory n.is cauterized– incision is made longitudinally along the lateral– using the suction and the bipolar


• Identification of the A1-ACoA-A2 Complex Vessels– dissection is then continued along the lateral aspect

of the ipsilateral A1 segment to identify the ipsilateral A2 segment

– Identified ipsilateral medial striate artery of Heubner and the orbitofrontal artery

– superior-pointing aneurysms• Can identified : contralateral A1 segment medial striate artery of Heubner• Hidden : contralateral A2


• Identification of the A1-ACoA-A2 Complex Vessels– inferior-pointing aneurysms

• Can identified : contralateral A2 segment medial striate artery of Heubner• Hidden : contralateral A1

– posterior-pointing aneurysms– may or may not obstruct the view of the contralateral A2 segment

– anterior-pointing aneurysms– may partially obstruct the view of the contralateral A2 segment or the contralateral A1 segment


• Identification of the A1-ACoA-A2 Complex Vessels– It is important to remember that because the A2

segments enter the interhemispheric fissure one anterior to the other

– Identified : A1 segments, exiting A2 segments, ACoA, medial striate arteries of Heubner, orbitofrontal arteries, and even frontopolar arteries, the critical perforators of the ACoA and A2 segments


• Dissection of the Aneurysm Neck– Superior-pointing aneurysms

• Advantage : being buried in the interhemispheric• Disadvantage : more intimately associated with the

hypothalamic and infundibular perforators• They usually do not rupture when the retractor is placed across the interhemispheric fissure during the exposure of the contralateral A1 segment.• Complicating : either one or both A2 segments may be densely adherent to the body of the aneurysm


• Dissection of the Aneurysm Neck– Posterior-pointing aneurysms

• Advantage : being buried in the interhemispheric• Disadvantage : the critical infundibular and

hypothalamic perforators characteristically surround the neck of this aneurysm

• Most difficult


• Dissection of the Aneurysm Neck– Anterior-pointing aneurysms

• Adherent to the gyrus rectus and may rupture during early subfrontal retraction

• More favorable relationship to the infundibular and hypothalamic perforator

• Complicating : orbitofrontal or a proximal frontopolar artery is often adherent to the wall of the aneurysm


• Dissection of the Aneurysm Neck– Inferior-pointing aneurysms

• Usually adherent to the optic chiasm, opticnerves, or interoptic space

• More favorable relation to the hypothalamic and infundibular perforators• Complicating : infundibular and hypothalamic perforators adherent to the posterior aneurysmal wall


• Aneurysmoplasty– rehydrate the sac with plenty of irrigation– wax the tips of the bipolar forceps to prevent sticking– reduce the bipolar current to as low as possible and

then increase it as necessary until it starts to shrink the wall


• No. 7 microdissector is gently passed into the spaces where the clip blades will be inserted

• It is important to ensure – that the entire neck is cleared– there is not a secondary lobe of the aneurysm that

could be punctured with the clip blade. When dissecting directly on the aneurysm

– sharp dissection with either an arachnoid knife or microscissors is better than blunt dissection


• Clip Selection and Application– The length of the selected clip should be at least 1.5

times the diameter of the aneurysm neck– a 10-mm neck requires at least a 15-mm clip

• Aspiration of the Dome– the dome is punctured and aspirated with a 25-gauge

spinal needle attached to a short segment of intravenous tubing and a 5-mL syringe filled with saline

• Papaverine Application

Complications• Clinical vasospasm• Hyponatermia

– common in higher grade– SIADH,CSW

• ACoA syndrome– impaired memory, personality changes, and

confabulation– result of a focal lesion in the basal forebrain

Anatomic And Morphologic Selection Criteria For Endovascular Treatment

• Microsurgical and endovascular treatments, both of which are safe and effective options in properly selected patients

• Relative contraindication : absent A1 segment• Clear visualization of the surrounding

vasculature and the neck and dome of the aneurysm must be obtained

Anatomic And Morphologic Selection Criteria For Endovascular Treatment

• The aneurysm neck and dome plays a significant role in determining the success or failure of an endovascular approach

• Higher rates of complete occlusion– Smaller– Anteriorly projecting ACoA aneurysms

• Higher rate of endovascular procedure–related complications– Posteriorly projecting ACoA aneurysms

Health & Medicine

368 ACoA aneurysm