stent - assisted coiling is a safe and effective method for treating wide - necked aneurysms1 ) , but ischemic stroke related to stent thrombosis is a major potential drawback .
all thromboses occur within one year after the initial procedure , very late stent thrombosis ( vlst ) , which is defined as stent thrombosis occurring one year after implantation2 ) , following sole stent - assisted coiling has not been previously reported . here , we report the first case of vlst , which occurred 14 months after a typical sole stent - assisted coiling procedure .
this case highlights the possible mechanism of vlst after single stent - assisted coiling and raises concerns about the duration of prophylactic antiplatelet therapy ( apt ) .
a 56-year - old woman presented with subarachnoid hemorrhage from a ruptured aneurysm in the anterior communicating artery ( acoa ) and an unruptured large aneurysm with an ultrawide neck involving the parent artery circumferentially at the right paraclinoid internal carotid artery ( ica ) ( fig .
the patient received oral aspirin ( 300 mg / d ) and clopidogrel ( 75 mg / d ) for 7 days before the coiling procedure , which was performed using a transfemoral approach under full anticoagulation with intravenous heparin ( activated clotting time > 250 s ) .
first , a closed - cell enterprise stent ( 4.537 mm ; cordis , miami lakes , fl , usa ) was navigated in the ica and implanted across the wide neck of the aneurysm , and coiling then was performed using 19 bare platinum coils ( orbit ; cordis , miami lakes , fl , usa ) via a sl-10 microcatheter ( boston scientific , natick , ma , usa ) , which was jailed outside the stent .
the final angiogram showed near complete obliteration of the aneurysm with minimal neck remnant ( fig .
the patient had an uneventful postoperative course and was neurologically normal at the out - patient department follow - up .
furthermore , follow - up angiography performed at 12 months after the coiling procedure depicted no change in the small amount of residual filling of the aneurysmal neck and a well - preserved parent artery without any thrombosis or stenosis ( fig .
the patient was maintained on dual antiplatelet therapy ( apt ) for 12 months after the initial treatment .
we used 300 mg aspirin and 75 mg clopidogrel as the dual antiplatelet regimen for 4 weeks followed by 200 mg aspirin and 75 mg clopidogrel for 5 months and 100 mg aspirin and 75 mg clopidogrel for the remaining 6 months .
after the 1-year follow - up angiographic evaluation , dual apt was switched to aspirin monotherapy .
two months after switching to aspirin monotherapy , the patient experienced transient ischemic attack symptoms .
computed tomography angiography revealed occlusion of the right ica at the level of stent implantation .
diffusion weighted imaging taken for evaluating ischemic symptoms demonstrated multiple embolic infarctions in the right hemisphere ( fig .
3a ) . digital subtraction angiography ( dsa ) revealed in - stent thrombosis extending from the cavernous ica to the distal ica ( fig .
the patient admitted stopping her aspirin medication prior to a dental procedure conducted 3 days before the ischemic event .
the patient was managed conservatively , because the potential risk of thrombus distal migration was considered to be high for interventional therapy .
clopidogrel 75 mg was added to aspirin 200 mg and low molecular heparin was administrated for 10 days .
a follow - up angiography showed completely resolution of the thrombosis with good flow through the parent artery ( fig .
a 56-year - old woman presented with subarachnoid hemorrhage from a ruptured aneurysm in the anterior communicating artery ( acoa ) and an unruptured large aneurysm with an ultrawide neck involving the parent artery circumferentially at the right paraclinoid internal carotid artery ( ica ) ( fig .
the patient received oral aspirin ( 300 mg / d ) and clopidogrel ( 75 mg / d ) for 7 days before the coiling procedure , which was performed using a transfemoral approach under full anticoagulation with intravenous heparin ( activated clotting time > 250 s ) .
first , a closed - cell enterprise stent ( 4.537 mm ; cordis , miami lakes , fl , usa ) was navigated in the ica and implanted across the wide neck of the aneurysm , and coiling then was performed using 19 bare platinum coils ( orbit ; cordis , miami lakes , fl , usa ) via a sl-10 microcatheter ( boston scientific , natick , ma , usa ) , which was jailed outside the stent .
the final angiogram showed near complete obliteration of the aneurysm with minimal neck remnant ( fig .
the patient had an uneventful postoperative course and was neurologically normal at the out - patient department follow - up .
furthermore , follow - up angiography performed at 12 months after the coiling procedure depicted no change in the small amount of residual filling of the aneurysmal neck and a well - preserved parent artery without any thrombosis or stenosis ( fig .
the patient was maintained on dual antiplatelet therapy ( apt ) for 12 months after the initial treatment .
we used 300 mg aspirin and 75 mg clopidogrel as the dual antiplatelet regimen for 4 weeks followed by 200 mg aspirin and 75 mg clopidogrel for 5 months and 100 mg aspirin and 75 mg clopidogrel for the remaining 6 months .
after the 1-year follow - up angiographic evaluation , dual apt was switched to aspirin monotherapy .
two months after switching to aspirin monotherapy , the patient experienced transient ischemic attack symptoms .
computed tomography angiography revealed occlusion of the right ica at the level of stent implantation . diffusion weighted imaging taken for evaluating ischemic symptoms demonstrated multiple embolic infarctions in the right hemisphere ( fig .
3a ) . digital subtraction angiography ( dsa ) revealed in - stent thrombosis extending from the cavernous ica to the distal ica ( fig .
the patient admitted stopping her aspirin medication prior to a dental procedure conducted 3 days before the ischemic event .
the patient was managed conservatively , because the potential risk of thrombus distal migration was considered to be high for interventional therapy .
clopidogrel 75 mg was added to aspirin 200 mg and low molecular heparin was administrated for 10 days .
a follow - up angiography showed completely resolution of the thrombosis with good flow through the parent artery ( fig .
stent - assisted coiling is increasingly being used to treat aneurysms6,11 ) , but , although this is an effective and relatively safe technique1 ) , it has inherent problems such as thromboembolic complications and in - stent stenosis10,18 ) .
the timing of stent thrombosis can be classified as acute ( < 24 h post procedure ) , early or subacute ( 24 h to 30 days post procedure ) , late ( 31 days to 1 year post procedure ) , or very late ( > 1 year post procedure)2 ) .
in - stent thrombosis within 1 year after stenting has been reported to occur at a rate of around 3% after stent - assisted coiling10,14,15,19 ) .
however , no report has previously described vlst following implantation of a sole stent , which is self - expanding intracranial stent designed for coiling assistance .
the mechanisms of vlst previously proposed are ; progressive in - stent stenosis , premature discontinuation of dual apt , delayed atypical response to adjacent polyglycolic acid - loaded " bioactive " coils , spontaneous occlusion of the parent artery , stenting across major arterial side branches , stent mal - apposition , stent fracture , stent strut penetration of the necrotic core , disruption of vulnerable plaque near the stent , radiation therapy , and hypersensitivity vasculitis4,7 ) . in our case ,
no in - stent stenosis or stenosis around the stented vessel was noted by 1-year follow - up angiography .
thus , premature discontinuation of antiplatelet medication was the likely cause of vlst in our case .
the prevention of thromboembolic complications after stenting is currently achieved with prophylactic dual apt12 ) , but the regimens and durations of prophylactic apt are controversial9,21 ) .
it is recognized intracranial stents are thrombogenic until stent endothelialization occurs , and that the duration of apt should be based on the completion of endothelialization .
it has been reported by some that endothelialization is complete within 6 months after bms implantation5,8,16 ) , but no human data is available regarding the rate of stent endothelialization after stent - assisted coiling . in the interventional cardiology field ,
current guidelines recommend dual apt for at least 1 month for bmss , but up to 1 year for drug - eluting stents , which cause delayed endothelialization22 ) .
however , in the neuroendovascular field , the optimal duration of prophylactic apt following stent - assisted coiling remains undefined , and clinical practices are highly discrepant ; some authors have recommended only 3 or 6 months of antiplatelet therapy after stent placement for coiling17,20 ) .
these recommendations seem to be based on the facts that the target vessel for stent placement is usually nonatherosclerotic and that stents being used for coiling assistance are of bare - metal and have self - expandable properties , and thus , do not delay endothelialization over stent struts or cause endothelial injury16 ) .
however , a much longer duration of apt may be required when stent endothelialization is only partially achieved .
the occurrence of vlst may mean that formation of a complete neointimal layer incorporating stent struts has failed despite the passage of considerable time after stent implantation .
our patient had a large aneurysm with a circumferential wide neck , which suggests a large portion of the stent might have unopposed the parent vessel . in addition
, it is likely that stent struts facing a circumferential wide aneurysmal neck are endothelialized at a far slower rate than that of a similar sized stents placed across a smaller aneurysmal neck .
these stents can be kinked or flattened in tortuous curves , which can result in incomplete stent apposition , causing incomplete endothelialization3,13 ) .
thus , the ultra - wide neck involving the parent artery circumferentially and the closed - cell stent deployed in the tortuous carotid siphon probably contributed to the incomplete stent endothelialization in our case .
although we present only a single case of vlst after sole stent - assisted coiling , our observation suggest that apt is needed for much longer period after sole stent - assisted coiling for a large aneurysm with an ultra - large circumferential wide neck .
a study is required to determine optimal apt regimens according to stent type , number , and aneurysm size , shape after stent - assisted coiling .
although vlst is extremely rare , it is a serious event with potentially devastating consequences .
this case demonstrates that long - term apt and patient strict adherence are required to possibly prevent this complication when a large portion of the stent is anticipated to be unopposed to the vessel wall .
 stent thrombosis is a major limitation of stent - assisted coiling , which is an effective method for treating wide - necked aneurysms . 
 although early in - stent thrombosis has been reported , very late stent thrombosis ( vlst ) ( > 1 year ) has not been reported following implantation of a single self - expandable stent designed for coiling . 
 herein , the authors present a case of vlst that occurred 14 months after single stent implantation in a large paraclinoid aneurysm with an ultra - wide neck involving the parent artery circumferentially . 
 this case indicates the need for establishing guidelines regarding the optimal duration of prophylactic antiplatelet therapy following stent - assisted coiling , which remains undefined in the neuroendovascular field . 
INTRODUCTION
CASE REPORT
History and procedure
Antiplatelet therapy
Very late thrombosis
Management of thrombosis
DISCUSSION
CONCLUSION