the first segment ( a1 ) of the anterior cerebral artery ( aca ) normally branches off from the terminal of the internal carotid artery ( ica ) , runs above the optic nerve , and courses anteromedially to join the anterior communicating artery ( acoa ) . an infraoptic aca is an exceedingly rare anomaly of the cerebral arterial system , which was first reported by robinson in 1959.2)4)14)16 ) this anomalous artery usually arises from the intradural ica near the level of the ophthalmic artery ( oa ) or rarely from the extradural ica , courses medially and horizontally as it passes under the ipsilateral optic nerve , and makes a sharp turn superiorly to join the acoa or distal branches.4)5 ) an azygous aca is another anomaly , with a prevalence of 0.2% to 4% , which represents a single unpaired aca featured as a solitary midline trunk that supplies both aca territories ; this anomalous artery is known to have an association with persistence of the embryonic median artery of the corpus callosum.13 ) both infraoptic and azygous acas have been reported in association with an increased risk of aneurysm formation . we report on an extremely rare case of a ruptured aneurysm at the infraoptic azygous aca with the contralateral ica agenesis , and introduce a feasible option for treatment of this aneurysm by y - stent assisted coil embolization . a 59-year - old female patient presented with a sudden bursting headache with a drowsy mentality . brain computed tomography ( ct ) scan confirmed the presence of a diffuse subarachnoid hemorrhage ( fig . 1 ) . digital subtraction angiography revealed a ruptured bilobulated broad neck aneurysm at the terminal of the infraoptic azygous portion of the aca where the bilateral distal acas branched off . this anomalous artery originated from the right ica proximal to the oa , suggesting the possibility of an extradural ica origin . the bilateral recurrent arteries of heubner arose from the vertical portion of the azygous aca in the midline , and coursed laterally to enter the anterior perforated substances . an aortogram showed the common origin of the brachiocephalic trunk and the left common carotid artery , known as the " bovine configuration " , and the left carotid angiogram revealed agenesis of the left ica , visualizing only the external carotid artery ( eca ) systems . the territory of the left middle cerebral artery ( mca ) was solely supplied via the prominent left posterior communicating artery ( pcoa ) . the aneurysm was bilobulated with the largest diameter of 8.36 mm and had a broad neck of 5 mm slightly incorporating the bilateral branches of the distal aca ( fig . a 6f shuttle guiding sheath ( cook medical , bloomington , in ) was transfemorally advanced into the right cervical ica . a rebar 18 microcatheter ( ev3 inc , irvine , ca ) was inserted , covering from the azygous aca to the proximal portion of the left distal aca , preparing for use of a solitaire ab ( ev3 inc , plymouth , mn ) afterward . an excelsior sl-10 microcatheter ( boston scientific , natick , ma ) was used for delivery of coils into the aneurysm . when the flow into the bilateral branches of the distal aca began to be compromised during coil packing , a solitaire ab was deployed into the previously installed rebar microcatheter and another solitaire ab was delivered into the right distal aca in y - configuration in order to preserve the bilateral distal aca . the patient later suffered severe vasospasm but recovered fully without neurological deficit after undergoing intraarterial nimodipine angioplasty ( fig . 4 ) . follow - up brain ct and coronal reconstructions of magnetic resonance ( mr ) angiography source images provided clarification of the anatomical configuration of the azygous aca with an infraoptic course in association with the optic nerve ( fig . 5 ) . an infraoptic course of the aca is an extremely rare vascular anomaly . since the first reported case in 1959 , approximately 50 cases of this anomaly have been reported during autopsy , surgery , or angiography.4)14)16)17 ) an infraoptic aca originating from the extradural ica was reported in only four of these previous cases.1)4)6)8 ) various terminologies , including infraoptic aca and carotid - aca anastomosis , have been used.12)14 ) this aca anomaly is characterized by three features : an anomalous artery branches off from the ica at the level of the oa , it courses beneath the optic nerve , and supplies the territory of the normal aca.9)12)17 ) our patient also presented with these features , and , in addition , showed an unusual anomaly of the contralateral ica agenesis with the prominent pcoa solely providing collateral flow to the mca territory ; these findings appeared to show a close association with formation of the azygous aca with the solitary midline trunk from where the bilateral branches of the distal aca and the bilateral recurrent arteries of heubner originated . the origin of this anomalous artery was proximal to the oa , possibly having an extradural location . the oa is the conventional anatomical landmark on angiography for differentiation between the intradural and extradural space ; it typically originates from the dorsal ica immediately adjacent to the dura . however , because the origin of the oa varies to some degree and the oa can not always be visualized on an angiogram , this landmark is not always reliable.1 ) in the present case , the origin of the oa was clarified on the lateral view of the right carotid angiogram , and the origin of this anomalous artery appeared to be cavernous or clinoid ica below the distal dural ring where the ica penetrates into the intradural space . there are three proposed theories : persistence of embryonic anastomosis between the primitive maxillary artery and the primitive olfactory artery , which later gives rise to the aca , persistence of in utero communication between the primitive dorsal and ventral ophthalmic arteries , and persistence and enlargement of prechiasmatic anastomosis between the prechiasmal branch of the oa and chiasmal branches of the aca.7)10)14)16)17 ) the infraoptic aca may be associated with other coexisting vascular anomalies , such as variants of carotid - basilar anastomosis , agenesis of the contralateral ica , anomalous origin of the oa from the eca , and fused pericallosal arteries.1)3)11)16 ) it can also accompany symptoms related to the optic nerve or optic chiasma compression.4)15 ) the prevalence of intracranial aneurysms in association with infraoptic azygous aca is high , probably due to local intrinsic structural and hemodynamic factors , and the most common site is the aca - acoa complex.3)6)7)8)11)12)15)16)17 ) however , according to previous reports , aneurysm formation may occur anywhere.1)4 ) diagnosis of this anomaly is important in planning for surgical treatment of the aca aneurysm . failure to notice the anomaly may result in unnecessary or inadequate dissection around the optic nerve , causing possible damage or excessive brain retraction in the effort to find the proximal aca , causing an intraoperative aneurysm rupture . surgical treatment of the aneurysm at the terminal portion of the infraoptic azygous aca may sometimes be difficult , because the hidden proximal aca behind the optic nerve would make proximal control inconvenient and the vertical midline segment of the proximal aca would frequently cause development of a superiorly directing aneurysm with a relatively high position . proximal control for aneurysm clipping may not be easy in an infraoptic location and the choice of surgical approaches between unilateral pterional versus bicoronal interhemispheric approaches , from its relatively high position in the midline , may be difficult ; therefore , coil embolization can be an alternative treatment option . in the case of a broad neck aneurysm at the azygous aca , preservation of bilateral distal branches of the aca is essential in order to prevent further neurological deficits . therefore , y - stent assisted coil embolization , which is often used for treatment of a basilar top aneurysm , may be a feasible option , when endovascular treatment is considered as obliteration method for a large broad neck aneurysm at the terminal of the infraoptic azygous aca . the infraoptic azygous aca is an extremely rare congenital anomaly related to interference in embryogenesis during the early stage of cranial artery development.4)16)17 ) the extradural origin of this anomaly is even more rare . it has a typical appearance on angiography : apparent low bifurcation of the ica with the aca arising near the oa , and a horizontal and medial course of the proximal aca as it passes under the optic nerve before turning superiorly to join the bilateral branches of the aca.4)5 ) it may accompany other vascular anomalies , such as variants of carotid - basilar anastomosis , or agenesis of the contralateral ica , as in our case . association of this anomaly with an intracranial aneurysm is frequent , and a detailed inspection of angiography is required when deciding on treatment modalities .
infraoptic anterior cerebral artery ( aca ) is an extremely rare congenital anomaly . 
 this anomalous artery usually arises from the intradural internal carotid artery ( ica ) near the level of the ophthalmic artery ( oa ) or rarely from the extradural ica . 
 this anomaly frequently harbors a cerebral aneurysm , and may involve other coexisting vascular anomalies . in the case of this anomaly , surgical treatment of the aneurysm at the proximal aca or anterior communicating artery ( acoa ) may sometimes be difficult , because the veiled proximal aca by the optic nerve would make proximal control inconvenient and the vertical midline segment of the proximal aca would frequently form a superiorly directing aneurysm with a relatively high position . 
 we report on an extremely rare case of a ruptured aneurysm at the infraoptic azygous aca , possibly having an extradural origin , accompanied by contralateral ica agenesis , and also introduce a feasible method for treatment by y - stent assisted coil embolization .