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nontraumatic subarachnoid hemorrhage ( sah ) is caused by rupture of a cerebral aneurysm in 80 - 90% of patients.4 ) unfortunately , aneurysmal sah has a high mortality rate of 45%.1 ) therefore , immediate diagnosis and treatment are very important in prevention of catastrophic deterioration .
digital subtraction angiography ( dsa ) remains the gold standard for the main technique for diagnosis of the intracranial aneurysms.4)5)7 ) computed tomography angiography ( cta ) is a rapid , less invasive modality for patients with intracranial aneurysm and useful for evaluation of patients with aneurysmal sah .
therefore , cta is more often used in the initial evaluation of sah.4)7)10)11)14 ) however , in some patients with a nontraumatic sah , no aneurysms are found on the initial dsa.3)9)11 ) contrast extravasation of a ruptured intracranial aneurysm during cta is rare , but is becoming more common , with increasing use of cta for various cerebral vascular diseases and increasing resolution of cta .
we report on two similar cases , but with different clinical course of contrast extravasation from the distal basilar artery ( ba ) during cta but negative findings of dsa .
a 66-year - old man was admitted to our hospital after sudden loss of consciousness .
a pre - enhanced cranial ct showed acute diffuse sah in the basal cistern ( fig .
the 3-dimensional cta showed a saccular lesion arising from the upper basilar artery and projecting anteriorly ( fig .
dsa performed one hour and a half later and did not show any vascular abnormality ( fig .
a repeat dsa , performed on postbleed day 10 , also showed no vascular abnormality .
the patient was treated conservatively and discharged after 30 days without any neurologic deficit . on follow - up at three months , the patient had no neurologic deficit , and follow up dsa also confirmed no vascular abnormality . a 55-year - old woman with a medical history of chronic viral hepatitis presented to our clinic after sudden onset of headache with vomiting .
the patient received an external ventricular drain ( evd ) for symptomatic hydrocephalus on posthemorrhage day 2 .
the patient 's clinical condition improved and her level of consciousness improved to alert immediate after evd . on the second day after evd ,
however , cerebral angiography at the same time confirmed a small cylinder like contrast stagnation from the upper basilar artery at late arterial phase , indicating pseudoaneurysm formation ( fig .
we inserted two solitaire stents ( 4  20 mm , ev3 , irvine , ca , usa ) for flow diversion and anticipating thrombus formation of the pseudoaneurysm .
the patient 's clinical course was uneventful , however , one - month follow up cta still showed a saccular lesion from the upper basilar artery .
dsa still showed contrast stagnation at late arterial phase on the upper basilar artery and superselective microcatheter angiography confirmed a pseudoaneurysm arising from a small perforating artery of the superior cerebellar artery ( sca ) ( fig .
4 ) . due to concern about cerebellar infarction , we could not sacrifice the sca . to facilitate thrombus formation of the pseudoaneurysm , we performed repeated temporary balloon occlusion using a sceptor xc balloon ( 4  10 mm , microvention , tustin , ca , usa ) and achieved decreased contrast inflow to the pseudoaneurysm ( fig . 5 ) . on follow - up at 11 months , the patient had no neurologic deficit , and she was able to live independently .
follow up dsa performed 11 months after hemorrhage confirmed no contrast stagnation and abnormal vascular lesion ( fig .
a 66-year - old man was admitted to our hospital after sudden loss of consciousness .
a pre - enhanced cranial ct showed acute diffuse sah in the basal cistern ( fig .
the 3-dimensional cta showed a saccular lesion arising from the upper basilar artery and projecting anteriorly ( fig .
dsa performed one hour and a half later and did not show any vascular abnormality ( fig .
a repeat dsa , performed on postbleed day 10 , also showed no vascular abnormality .
the patient was treated conservatively and discharged after 30 days without any neurologic deficit . on follow - up at three months , the patient had no neurologic deficit , and follow up dsa also confirmed no vascular abnormality .
a 55-year - old woman with a medical history of chronic viral hepatitis presented to our clinic after sudden onset of headache with vomiting .
the patient received an external ventricular drain ( evd ) for symptomatic hydrocephalus on posthemorrhage day 2 .
the patient 's clinical condition improved and her level of consciousness improved to alert immediate after evd . on the second day after evd ,
a repeat cta after rebleeding did not show an abnormal vascular lesion . however , cerebral angiography at the same time confirmed a small cylinder like contrast stagnation from the upper basilar artery at late arterial phase , indicating pseudoaneurysm formation ( fig .
we inserted two solitaire stents ( 4  20 mm , ev3 , irvine , ca , usa ) for flow diversion and anticipating thrombus formation of the pseudoaneurysm .
the patient 's clinical course was uneventful , however , one - month follow up cta still showed a saccular lesion from the upper basilar artery .
dsa still showed contrast stagnation at late arterial phase on the upper basilar artery and superselective microcatheter angiography confirmed a pseudoaneurysm arising from a small perforating artery of the superior cerebellar artery ( sca ) ( fig .
4 ) . due to concern about cerebellar infarction , we could not sacrifice the sca . to facilitate thrombus formation of the pseudoaneurysm , we performed repeated temporary balloon occlusion using a sceptor xc balloon ( 4  10 mm , microvention , tustin , ca , usa ) and achieved decreased contrast inflow to the pseudoaneurysm ( fig .
5 ) . on follow - up at 11 months , the patient had no neurologic deficit , and she was able to live independently .
follow up dsa performed 11 months after hemorrhage confirmed no contrast stagnation and abnormal vascular lesion ( fig .
in the current cases , we report on two patients with contrast extravasation from the basilar artery seen on cta , but negative findings with immediate subsequent cerebral angiography .
incidence of patients with sah of unknown etiology was approximately 10 to 30%.3)5)9)12 ) the precise cause of angiogram - negative sah is unclear .
however , patients with angiogram - negative sah have a more favorable prognosis and lower rebleeding rate than those with other distributions of aneurysmal sah.3)9)11)12 ) dsa has been the gold standard method for identification and diagnosis of intracranial aneurysms .
however , dsa has some weakness of being very invasive and takes time to performed .
the risk of complications has been reported as 0.9% to 2.3% with permanent deficit in 0.3%4 ) and 0.6% of cases occurring in the non - severe neurologic complications , include formation of hematoma , peripheral thromboembolic events , transient hypotension , arteriovenous fistulas , or infection.2)4 ) recently , cta is useful for detection of intracranial aneurysms because it is less invasive and the procedure is easier to perform than dsa .
because contrast media for cta is injected intravenously , it is less invasive than arterial injections required for dsa.7 ) therefore , cta is now used as the diagnostic method of first choice for detection of aneurismal sah , vascular malformations , stenotic vessel disease , vasospasm , traumatic vessel disease , and for development of an occupational treatment plan.4)10)14 ) sensitivity of cta for detection of intracranial aneurysms between 83.6% and 92.7% has been reported , and the specificity is between 77.2% and 98.9%.4 ) due to the increased usefulness , sensitivity and specificity for detection of intracranial aneurysms , use of cta has recently become more frequent . however , cta has still not replaced dsa as the standard method for detection of intracranial aneurysms .
the disadvantages of cta were difficulty in distinguishing small perforating arteries with a diameter less than 1 mm , difficulty in discriminating a infundibular dilatation of the arterial origin from an aneurysm , artifact of the adjacent vessel , display of venous systems imitating aneurysms , and extravasated blood such as hemorrhage surrounding the aneurysm imitating vascular structures .
almost all extravasation occurs from ruptured aneurysms but has also been reported in association with other rare situations such as microangioma , infarction with sah due to obliteration of a perforating artery or increase in arterial pressure after the injection of contrast media.8)10 ) another potentiality of extravasation is very small sized true aneurysmal sah that is not large enough to be recognized .
extravasation on cta has been reported previously , such as the " cap sign " , " corkscrew sign " , " puddling " and the " spot sign " . the " cap sign " and the " corkscrew sign " are some kind pattern of extravasation .
the " puddling " means multiple areas of contrast media on cta and the " spot sign " is enhancing foci within a hematoma mass associated with hematoma growth and poor prognosis.7)13)14 ) nevertheless , sometimes dsa did not reveal a lesion that was initially detected on the cta . failure to detect an aneurysmal rupture by dsa that was detected on the initial cta has been ascribed to a result of vasospasm , dissecting aneurysm , spontaneous thrombosis of the aneurysm , microaneurysm , or error of interpretation.5)11 ) aneurysms detected on cta that do not present on initial
some authors have previously reported discovery rates of repeat dsa of occult aneurysms overlooked on the initial dsa of 2 and 36%.5)6)11 ) in the second case , we found a small cylinder like vascular abnormality , which was confirmed by repeated dsa after rebleeding .
first bleeding was due to rupture of a small perforating vessel arising from the superior cerebellar artery and then spontaneous thrombosis occurred .
therefore , we could not detect vascular abnormality on dsa despite detection of a saccular lesion on initial cta .
flow diversion through double stents and temporary balloon occlusion could facilitate thrombosis within the pseudoaneurym .
we reported on extremely rare cases of two patients who showed nonaneurysmal , angiogram - negative sah in which supposed contrast extravasation on initial cta mimicked a basilar artery trunk aneurysm . based on our experience ,
if we encounter a patient with extravasation on cta with negative dsa findings , repeated dsa is mandatory and superselective microangiography could reduce false - negative finding and improve understanding of pathophysiology .
contrast extravasation on computed tomography angiography ( cta ) is rare but becoming more common , with increasing use of cta for various cerebral vascular diseases . 
 we report on two cases of spontaneous subarachnoid hemorrhage ( sah ) in which the cta showed an upper basilar trunk saccular lesion suggesting ruptured aneurysm . 
 however , immediate subsequent digital subtraction angiography ( dsa ) failed to show a vascular lesion.in one case , repeated follow up dsa was also negative . the patient was treated conservatively and discharged without any neurologic deficit . in the other case , 
 the patient showed sudden mental deterioration on the third hospital day and her brain ct showed rebleeding . 
 the immediate follow up dsa showed contrast stagnation in the vicinity of the upper basilar artery , suggestive of pseudoaneurysm . 
 double stents deployment at the disease segment was performed.due to the frequent use of cta , contrast extravasation is an increasingly common observation . 
 physicians should be aware that basilar artery extravasation can mimic the appearance of an aneurysm .