Microsurgery of Distal Anterior Cerebral Artery Aneurysms

Youmans,Neurological surgery 6th chapter 369Andrew F. Ducruet, E. Sander Connolly Jr

12/01/59

Distal anterior cerebral artery (DACA) aneurysms

• aneurysms arise on the ACA or its branches distal to the ACoA

• uncommon• most commonly at the bifurcation of the

pericallosal and callosomarginal arteries• less than 5 mm,giant is rare• common association with additional

intracerebral aneurysms : MCA bifurcation or ICA bifurcation

Etiology

• Spontaneous• Mycotic or infectious

– septic emboli from vegetative heart– inflammatory reaction leads to a loss of intima and elastic tissue– often involves much of the circumference of the vessel

• Traumatic– shearing forces exerted on the distal pericallosal artery at the

lower level of the falx• Tumor emboli

– most commonly observed in patients with atrial myxomas

Relevant Anatomy

Perlmutter and Rhoton• A1 : ACA proximal to ACoA• A2 : ACoA to the junction of the rostrum and genu of corpus callosum

– Orbitofrontal a.– Frontopolar a..

• A3 : extends from the genu to a point where the artery makes a posterior turn above the genu– anterior middle, posterior internal frontal a.– callosomarginal a

• A4 : posterior extension of the artery from A3 and extends to a point bisected by the coronal suture– paracentral a.

• A5 : extends distally to include the anastomoses with the splenial arteries– superior and inferior parietal a.

variants in distal ACA anatomy

Clinical Presentation• 50 years• Female• 4 vessel angiogram : undiscover aneurysm• SAH

– often prominent in the interhemispheric fissure across the top of the corpus callosum

– frontal hematoma : Mutism,memory loss– IVH : frontal horn of lateral ventricle– Intracallosal hemorrhage

Surgical Considerations• Microsurgically first line

– peripheral location– small size– unfavorable neck-to-parent artery ratio– tendency to “blow out” the bifurcation at

which they occur– amount of brain retraction and muscle

dissection needed to clip these lesions is comparatively minimal relative to other aneurysms

Surgical Considerations

• Endovascular treatment– extreme age– significant medical comorbidities– poor neurological condition– irreversible coagulopathy

Surgical Considerations• unruptured DACA aneurysm and a ruptured

aneurysm at another location– repairing all aneurysms during one procedure to

facilitate treatment of vasospasm with hemodynamic therapy

– repair only the ruptured aneurysm and leave the unruptured DACA aneurysm because it requires both extending the craniotomy and further brain manipulation and operative time

Preoperative Preparation• Normovolemia• Normotension• Hydrocephalus EVD• PPI• ATB• Anti-seizure drug

Positioning• Just at or distal to the genu of the corpus

callosum– supine with head in neutral position

• lies below or proximal to the genu of the corpus callosum– supine with head extened

• Just above the ACoA– supine head rotated 15 to 30 degrees away and

maximally extended

Skin Incision and Craniotomy• Proxinal A2 lesion

– bicoronal, modified bicoronal, or pterional incision– with or without orbital or orbitozygomatic extension

• Callosomarginal artery, origin in the region of the genu– modified bicoronal scalp incision– parasaggital craniotomy

Skin Incision and Craniotomy

Microsurgical Dissection• Dura

– cruciate fashion with a medial triangular dural flap based on the superior sagittal sinus

– not to thrombose the sinus nor to interrupt any of the bridging veins large vein

– anterior to the coronal suture may be taken without risking venous infarction

• Microscope, brain retractor and cortical surface of the frontal lobe is covered with Telfa

Microsurgical Dissection• Frontal lobe is gently dissected from the falx

– A 2- to 3-cm working corridor is developed– exposure of the cingulate gyri bilaterally– identification of the callosomarginal a.

• Base of the cingulate gyri lies the cistern of the corpus callosum– pericallosal arteries– both arteries must be identified and followed

proximally– if a frontal lobe hematoma limits the exposure, a

small cortical incision may be made to partially decompress the brain

Microsurgical Dissection• Aneurysm usually points superiorly and

forward along with the callosomarginal artery– dissect forward on the inferior surface of the

pericallosal vessels to where they begin to dive around the genu of the corpus callosum

– resecting a small portion of corpus callosum often brings the proximal trunks into view for temporary control

• Dissection of aneurysm• Clip placement

– perpendicular or parallel to the pericallosal artery

Complication• Embolization from the aneurysm dome and

tearing of the thin-walled aneurysm• Intraoperative rupture with prolonged trapping

has also been seen and can lead to ischemia in the ACA territory

• Frontal bridging brain tear– venous infarction

• Vasospasm– focal distal spasm involving the DACA segments may

be difficult to treat with angioplasty and hemodynamic therapy

Clinical Series

Clinical Series