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although spontaneous thrombosis of large and giant aneurysms is not uncommon , this situation in a small ruptured cerebral aneurysm is a rare event with incidence of 1 - 2% .
its possible pathophysiology with contributing factors has been well discussed in the literature.1)2)3)8)12)15)18 ) in addition , subsequent recanalization within the next few weeks has also been described .
we report on a case of acute thrombosis of the aneurysm , which occurred immediately after coil extraction , and suggest the next way to prevent recanalization , which can lead to re - rupture of the aneurysm .
a 54-year - old male experienced a sudden onset of headache which had developed 2 days ago .
after the initial diagnosis of subarachnoid hemorrhage ( sah ) using brain computed tomography ( ct ) in another hospital , he was transferred to the emergency room where his glasgow coma scale score was e4v5m5 . despite neck stiffness , there was no focal neurological sign .
a brain ct scan taken on admission showed focal sah concentrated in the anterior portion of the basal cistern ( fig .
1 ) . digital subtraction angiography ( dsa ) confirmed the presence of the anterior communicating artery ( acoa ) aneurysm and 3d rotational angiography ( 3dra ) showed that the aneurysm had a very narrow neck , which measured 5.9  2.7  1.7 ( width  height  neck diameter ) ( fig .
as morphologic features of the aneurysm were adequate for coil embolization , we decided to perform an emergency endovascular coil embolization on the day of admission .
dsa was performed again to assure the aneurysm . after confirming that the result on dsa was identical to the previous one , a microcatheter
was carefully guided over a microguidewire into the aneurysm . as the tip of the catheter was kept at the neck of the aneurysm , the first coil ( target detachable coil 3 mm  8 cm ; stryker neurovascular , fremont , ca , usa ) placement was attempted very slowly . at the last moment of deploying the first coil ,
the tip of the microcatheter was seen to move back from the aneurysm and the projection of the coil loop outside the aneurysm was observed ( fig .
however , a subsequent angiogram showed near obliteration of the aneurysm without evidence of vasospasm .
because acute thrombosis facilitated by an exposed coil within the aneurysm was assumed , and , sooner or later , recanalization could occur , we decided to insert a smaller coil into the remaining stump of the neck . with the coil ( hypersoft 3d complex coil 2 mm  4 cm ; microvention , tustin , ca , usa )
, embolization was performed safely and post - embolization dsa showed complete occlusion of the aneurysm ( fig .
there was no occurrence of procedure - related complication during coil embolization and the patient recovered without neurologic deficit after the procedure .
follow - up dsa the next day showed persistent occlusion of the aneurysm ( fig .
the patient was discharged without neurologic deficit of the modified rankin scale score 0 . magnetic resonance ( mr )
angiography at 3-month follow - up showed no evidence of residual neck or recurrence of recanalization . on
1 year follow - up dsa , despite change in the configuration of the coil , the aneurysm remained to be completely obliterated ( fig .
a 54-year - old male experienced a sudden onset of headache which had developed 2 days ago .
after the initial diagnosis of subarachnoid hemorrhage ( sah ) using brain computed tomography ( ct ) in another hospital , he was transferred to the emergency room where his glasgow coma scale score was e4v5m5 . despite neck stiffness , there was no focal neurological sign .
a brain ct scan taken on admission showed focal sah concentrated in the anterior portion of the basal cistern ( fig .
1 ) . digital subtraction angiography ( dsa ) confirmed the presence of the anterior communicating artery ( acoa ) aneurysm and 3d rotational angiography ( 3dra ) showed that the aneurysm had a very narrow neck , which measured 5.9  2.7  1.7 ( width  height  neck diameter ) ( fig .
as morphologic features of the aneurysm were adequate for coil embolization , we decided to perform an emergency endovascular coil embolization on the day of admission .
dsa was performed again to assure the aneurysm . after confirming that the result on dsa was identical to the previous one , a microcatheter
as the tip of the catheter was kept at the neck of the aneurysm , the first coil ( target detachable coil 3 mm  8 cm ; stryker neurovascular , fremont , ca , usa ) placement was attempted very slowly . at the last moment of deploying the first coil , the tip of the microcatheter was seen to move back from the aneurysm and the projection of the coil loop outside the aneurysm was observed ( fig .
however , a subsequent angiogram showed near obliteration of the aneurysm without evidence of vasospasm .
3b ) . because acute thrombosis facilitated by an exposed coil within the aneurysm was assumed , and , sooner or later
, recanalization could occur , we decided to insert a smaller coil into the remaining stump of the neck . with the coil ( hypersoft 3d complex coil 2 mm  4 cm ; microvention , tustin , ca , usa )
, embolization was performed safely and post - embolization dsa showed complete occlusion of the aneurysm ( fig .
there was no occurrence of procedure - related complication during coil embolization and the patient recovered without neurologic deficit after the procedure .
follow - up dsa the next day showed persistent occlusion of the aneurysm ( fig .
the patient was discharged without neurologic deficit of the modified rankin scale score 0 . magnetic resonance ( mr )
angiography at 3-month follow - up showed no evidence of residual neck or recurrence of recanalization . on
1 year follow - up dsa , despite change in the configuration of the coil , the aneurysm remained to be completely obliterated ( fig .
the reported incidence of acute thrombosis of the aneurysm after sah is 1 - 2%,7)9)17 ) and several possible mechanisms have been reported in the literature . in large or giant aneurysms , in particular ,
the incidence of spontaneous total thrombosis of the aneurysm has shown a marked increase , ranging from 13% to 20%,10 ) and the volume - to - orifice ratio of the aneurysm has been suggested as the most reliable mechanism of spontaneous thrombosis.1 ) however , in small aneurysms , other factors including anti - fibrinolytic agent , non - ionic contrast media , systemic hypotension , increased blood coagulability , increased platelet aggregation , vasospasm , and hemodynamics in the parent artery have also been suggested as an influential mechanism.3)6)8)15)18)20 ) in our patient , we supposed several factors that promoted thrombosis of the aneurysm .
the most important and potent factor was a narrow neck of the aneurysm of 1.7 mm with a large volume - to - orifice ratio .
extremely narrow neck of the aneurysm was regarded as sufficient potential to induce thrombosis under special circumstances like the following .
first , the endovascular procedure - including microcatheter placement on the neck of the aneurysm and aborted first coil - could interrupt the intrasaccular blood flow and trigger aneurysm thrombosis .
second , inadequate systemic heparinization might induce spontaneous thrombosis . according to the protocol of our institute
, we generally induce systemic heparinization after successful placement of the first basket coil in treatment of a ruptured cerebral aneurysm . in this patient ,
systemic heparin was not administered during the procedure , and the endovascular procedure was performed under inadequate systemic heparinization .
third , induced hypotension during the procedure could be a potential factor in spontaneous thrombosis . from this experience ,
if the neck of a ruptured aneurysm was very narrow , a rapid and adequate endovascular procedure , sufficient heparinization and exclusion of excessive hypotension during the procedure should be considered in order to avoid spontaneous thrombosis of the ruptured aneurysm .
lee et al.13 ) pointed out that the mechanism of recanalization might be the result of liquefaction of the thrombus and subsequent intrathrombotic dissection by blood flow .
another opinion regarding recanalization following thrombosis of the aneurysm suggests that when the thrombosis was induced by endovascular treatment , recanalization of the thrombosed aneurysm might occur spontaneously.14 ) although the pathophysiology of spontaneous recanalization has not been fully elucidated , recanalization ensuing from complete thrombosis of aneurysms has been reported in many studies.4)5)11)12)16)19)21)22 ) in these studies , recanalization of acute thrombosis of the aneurysm was observed in the days and weeks after thrombosis .
therefore , follow - up angiogram and careful observation during the follow - up period are required for fear of recanalization resulting in rebleeding of the aneurysm . in our patient , coil embolization was performed using a small coil in the tiny stump of the remaining neck .
we believed that this procedure might prevent spontaneous recanalization rather than inducing recanalization because the inserted coil would generate an additional thrombus as much as to block the narrow neck , thus resulting in obstruction of blood flow .
fortunately , a satisfactory result was obtained with complete occlusion of the aneurysm after 1-year follow - up .
thrombosis in a ruptured small aneurysm may be generated during coil insertion and the extraction process when the neck of the aneurysm is very narrow . because recanalization may occur within the next few weeks
, we believe that coil insertion on the remaining neck would provide a measure to prevent spontaneous recanalization .
spontaneous thrombosis of a ruptured aneurysm during coil embolization is a rare event , and some reports on recanalization of a spontaneous occluded ruptured aneurysm have been published . 
 we report on a case of a 54-year - old male who presented with a subarachnoid hemorrhage due to rupture of a small aneurysm of the anterior communicating artery ( acoa ) . 
 cerebral angiography confirmed the presence of the acoa aneurysm , but , during coil embolization , the aneurysm was near completely occluded with a remaining small neck . 
 a small coil was inserted into the remaining stump of the neck to prevent recanalization , and the angiographic result at 1 year after coil embolization showed complete obliteration of the aneurysm .