distal anterior inferior cerebellar artery ( aica ) aneurysms are extremely rare and account for 0.1% of all cerebral aneurysms.15 ) as with posterior circulation aneurysm in general , surgical treatments are often limited by the narrow angle of approach available for the cerebrovascular surgeon , the presence of brainstem perforators , the deep location of critical neurovascular anatomy , and difficulty in accessing adequate proximal control .
evolving endovascular treatments add to the several available management options , making a review of these lesions timely .
however , parent artery occlusion resulted in postoperative hearing loss and vertigo in most cases.3 ) we describe a case of aica aneurysm distal to the meatal loop treated with endovascular coils without compromising the aica flow .
a 42-year - old woman with no underlying diseases was referred to our department for severe headache , nausea , and vomiting after coitus .
computed tomography ( ct ) and magnetic resonance image ( mri ) showed a subarachnoid hemorrhage ( sah ) on the cerebellopontine angle cistern , and a small vermian intracerebral hemorrhage ( ich ) and intraventricular hemorrhage ( ivh ) in the fourth ventricle ( fisher grade 4 ) ( fig .
digital subtraction angiography revealed an aneurysm arising on the branching point between the caudomedial and rostrolateral branch of the left distal aica , located distally from the meatal loop .
2 ) and was 2.72.8 mm with a neck of 1.5 mm directed caudo - laterally .
the diameter of aica proximal to aneurysm was 0.8 mm on 3d rotational angiogram ( fig .
a 6f envoy guiding catheter ( cordis neurovascular , bridgewater , nj , united states ) was placed on the right vertebral artery ( va ) at the level of c2 vertebra .
an excelsior sl-10 microcatheter ( boston scientific , natick , ma , united states ) and x - pedion-14 microwire ( ev3 endovascular , inc . ,
plymouth , mn , united states ) were advanced to the right va and the basilar artery . under the roadmap guidance
, aneurysm selection was tried . even though the superselection of the aica orifice was not difficult , aneurysm selection was very difficult due to the tortuous course of aica and relatively small diameter of the aica for accommodation of the microcatheter ( fig .
after failed multiple trials of selecting the aneurysm with excelsior sl-10 microcatheter and x - pedion-14 microwire , we changed the microwire to x - pedion-10 , resulting in successful distal aica aneurysm selection .
the aneurysmal sac was then obliterated completely without compromise of the aica branch even though the second coil was extruded from the aneurysmal sac during coiling ( fig .
4 ) . postoperative ct showed slightly increased cerebellar hemorrhage , but there was no evidence of obstructive hydrocephalus .
however , she complained of hearing loss and tinnitus despite the patent flow to left aica .
typically , the artery arises from the junction at the middle and the lower thirds of the basilar artery , courses along the pons and the middle cerebellar peduncle , to which it gives a few important perforating branches.8 ) the branches of the aica that supply the inferior upper part of the olive arise 3~18 mm distal to the origin of aica , whose occlusion could lead to a lateral inferior pontine syndrome.1)10)16)19 ) near the facial - vestibulocochlear complex , the aica bifurcates into two major branches , called the rostrolateral and caudomedial branch .
the rostrolateral branch courses toward the internal auditory canal close to the seventh and the eighth cranial nerve complex and gives off the labyrinthine artery , also called the internal auditory artery ( iaa ) .
the caudomedial branch courses medially close to the pons , to which it sends a few perforators , and terminates in cerebellar branches.11)13 ) the aica also sends a few branches to the choroid plexus protruding from the foramen of luschka.11 ) the hemispheric branches from the aica frequently have anastomoses with the superior cerebellar artery and posterior inferior cerebellar artery.11)16 ) according to zager et al.,20 ) if the aneurysm is located on the segment of the aica that is distal to any branches coursing to the brainstem , distal occlusion may be performed without neurologic sequel .
however , that carries the risk of retrograde thrombosis , which can result in a devastating brainstem infarct .
major complications can be prevented by antithrombotic therapy after the procedure.4 ) smaltino et al.14 ) reported anatomical studies on the iaa , performed by mezzogiorno and delula . in their study ,
the iaa arose from the aica 87% of the time , and originated directly from the basilar artery ( ba ) in 10% .
this vessel usually gives off one branch to the cerebellum before joining the internal auditory canal .
therefore , it is called the cerebello - labyrinth artery.14 ) wende et al.,18 ) using angiography of the iaa , found that in 45.4% of the cases , it arose from the aica , in 24.4% from the superior cerebellar artery , and in 16% directly from the basilar artery . in addition , it had an average lumen of only 200~300 . in our case , even though the iaa could not be visualized on fully magnified angiogram and microcatheter angiogram of the aica , the iaa was presumed to originate from the distal aica based on the sensorineural hearing loss occurring after embolization .
distal aica aneurysms are frequently dissecting in nature , thus usual treatment is direct surgical trapping . compared with a surgical approach of distal aica aneurysm , endovascular treatment prevents massive bleeding and cerebellar injury during craniotomy and can spare the distal aica without trapping .
embolization without parent artery occlusion is difficult , and if the aneurysm originated from arterial dissection , it has a high risk of regrowth and rerupture.2)5)7 ) choi et al.2 ) reported a distal aica aneurysm at the meatal loop treated with parent artery preservation .
even though the dome of the aneurysm was occluded successfully , that patient experienced a recurrent hemorrhage from the recanalized aneurysm one month after the embolization .
the parent artery at the proximal portion of the aneurysm was then occluded with excellent results . however , in our case , the distal aica aneurysm was treatable with endosaccular coil embolization , since it was a saccular aneurysm with a definite neck rather than a dissecting aneurysm .
we performed successful coil embolization of the distal aica aneurysm without compromise of the parent artery .
ishii et al.4 ) reported that after coil embolization of a postmeatal aica , their patient presented with a high grade sensorineural hearing loss , probably related to the sacrifice of the labyrinthine artery .
perlman et al.12 ) showed that interruption of the blood supply to the cochlea caused immediate and complete loss of function and concluded that the hair cells were particularly vulnerable to ischemic injury.17 ) takeda et al.17 ) used a gerbil model of cochlear ischemia wherein animals were subjected to lethal cochlear ischemia for 15 minutes of extracranial occlusion of bilateral vertebral arteries .
hair cells on the basal turn are more vulnerable to ischemia than those at the apical turn,6 ) since the rate of oxygen consumption in basal turn is higher ( approximately 2.5-fold ) than at the apical turn , and the aerobic metabolism more active.9 ) in our case , the left aica parent artery mean diameter was about 0.8 mm , while the proximal and distal diameter of excelsior sl-10 microcatheter were about 0.8 and 0.56 mm , respectively . because the aica diameter could not accommodate the microcatheter , there was a high risk of vasospasm and catheterization failure if we remove the microcatheter during the procedure .
thus , the microcatheter was placed in the aica during the entire procedure time of two hours .
we think that another reason for the ischemic change is the aica traction due to its tortuous course .
a possible reason for postoperative hearing loss , in spite of the patent distal two branches on postoperative angiogram , is hemodynamic ischemia to the cochlea hair cells .
endovascular treatment of distal aica aneurysm beyond the meatal loop is feasible for preserving the aica flow .
however , because the cochlear hair cell is vulnerable to ischemia , unilateral hearing loss can occur , possibly from temporary reduction of the aica flow by the microcatheter during endovascular treatment .
 a 42-year - old woman presented with hunt and hess grade ( hhg ) iii subarachnoid hemorrhage ( sah ) caused by a ruptured left distal anterior inferior cerebellar artery ( aica ) aneurysm . computed tomography showed a thin sah on the cerebellopontine angle cistern , and small vermian intracerebral hemorrhage and intraventricular hemorrhage in the fourth ventricle . 
 digital subtraction angiography revealed the aneurysm on the postmeatal segment of left distal aica , a branching point of rostrolateral and caudomedial branch of the left distal aica . despite thin caliber , tortuous running course and far distal location , 
 the aica aneurysm was obliterated successfully with endovascular coils without compromising aica flow . 
 however , the patient developed left side sensorineural hearing loss postoperatively , in spite of definite patency of distal aica on the final angiogram . 
 she was discharged home without neurologic sequela except hearing loss and tinnitus.endovascular treatment of distal aica aneurysm , beyond the meatal loop , is feasible while preserving the aica flow . however , because the cochlear hair cell is vulnerable to ischemia , unilateral hearing loss can occur , possibly caused by the temporary occlusion of aica flow by microcatheter during endovascular treatment . 
INTRODUCTION
CASE REPORT
DISCUSSION
CONCLUSIONS