the anterior choroidal artery ( achoa ) supplies several important structures including the optic tract , geniculate body , posterior limb of internal capsule , globus pallidus , cerebral peduncle , uncus , amygdala , ventrolateral nucleus of thalamus , and choroid plexus . the vascular injury of achoa may result in severe neurological deficits such as hemiplegia , hemianesthesia , hemianopsia , decreased consciousness , and extrapyramidal symptoms . therefore , complete knowledge about vascular anatomy of achoa is very important before surgical or endovascular manipulations . although several detailed reports about anatomical variations of achoa have been reported , transposition of achoa as to posterior communicating artery ( pcoma ) origin was demonstrated only in 3 reports2 - 4 ) . we report a case with ruptured cerebral aneurysm arising from pcoma , which originated from the internal carotid artery ( ica ) distal to the origin of achoa . a 40-year - old woman presented with sudden onset of headache . computed tomography ( ct ) revealed subarachnoid hemorrhage ( sah ) which was slightly predominant in the left basal and sylvian cisterns . two small aneurysms arose from both distal supraclinoid ica , these were observed on ct angiograms ( fig . cerebral angiography demonstrated a small aneurysm arising from left fetal type of pcoma with suspicion of rupture and the other small aneurysm originating from right pcoma or perforating branch of ica . in this study , left achoa originated from ica proximal to the origin of fetal type of pcoma ( fig . achoa usually arises from the posterolateral wall of ica , a few mm distal to the origin of pcoma , and it provides blood supply to the important neural structures around crural and ambient cisterns . the achoa can have several variations in the course , size , number , branching pattern , and brain region supplied by this artery1 ) . among them , there have been several anomalies related to the origin of achoa including transposition of achoa and pcoma , origin from pcoma , origin from junction of ica and pcoma , and origin from middle cerebral artery4,5 ) . the clinical findings of transposed achoa cases including present one are summarized in table 1 . all of the transpositions of achoa occurred in the left side . among all the cases , our case showed sah due to ruptured aneurysm arising from fetal type of pcoma among multiple cerebral aneurysms founded and achoa originating from ica proximal to pcoma . typically , achoa runs posteromedially within the crural cistern and continues ambient cistern to enter the choroidal fissure . the proximal portion of this artery is cisternal segment and following portion becomes intraventricular segment1 ) . the transposed achoa in the previous cases including ours did not seem to affect the vascular territory or course despite of unusual vascular arrangements . the achoa can be exposed or manipulated in surgical approaches into the pathological lesions around temporal lobe or involving supraclinoid ica . although the achoa aneurysms accounting for 4% of all cerebral aneurysms are not so common , vascular injury of achoa with small caliber supplying the eloquent areas may be critical because of the possibility of significant morbidity and mortality . and , another caution is that achoa do not have significant collateral flows despite a potential anastomosis with posterior choroidal artery3 ) . we tried to preserve pcoma itself and all perforating branches arising from it because of the possibility to compromise the collateral flows of fetal type pcoma . it is notable that careful review of the preoperative angiograms helps to find unexpected vascular anomalies which may impose an additional surgical risk .
the anterior choroidal artery has several kinds of variations . among them , 
 the transposition of anterior choroidal artery and posterior communicating artery origins has been extremely rare . 
 we report a case with cerebral aneurysm arising from posterior communicating artery which origin was distal to the anterior choroidal artery and review the relevant literature .