the etiologies of intracranial artery dissection are various , the exogenous triggers like trauma , infection as well as inherited connective tissue disorders like moyamoya disease , fibromuscular dysplasia , and marfan 's syndrome .
alpha 1 antitrypsin deficiency and hyperhomocysteinemia are also distributing factors of carotid artery dissection19,25 ) .
the internal carotid artery dissection is responsible for less than 2% of all stroke and for 10 - 20% of stroke of young adults22 ) .
the dissection tends to occur in proximal internal carotid artery ( ica ) and rare in distal ica except when the cause is exogenous such as infection .
dissecting aneurysms of the intracranial posterior circulation are also rare that produce acute brain stem infarction or hemorrhage in young , healthy patients13,28,29 ) .
we report a case of multiple dissecting aneurysms of left superior cerebellar artery ( sca ) , left posterior inferior cerebellar artery ( pica ) and right pericallosal artery in patient who presented with subarachnoid hemorrhage .
we will also discuss of the relevance between dissecting aneurysm with the patient 's medical history , thrombocythemia .
a 42-year - old man was admitted to emergency room with a history of decrease in the level of consciousness .
he had no previous event of motor weakness or dizziness before the onset of mental change .
he had past medical history of hereditary spherocytosis and underwent splenectomy . during the follow up ,
his bone marrow biopsy reported megakaryocytic hyperplasia and he was diagnosed to essential thrombocythemia ( et ) . after a year , he was diagnosed to cerebral infarction and had been taking oral anti - platelet agent , since then .
the routine laboratory tests were normal except the platelet count , 660 k / ul . serum elastase was also within normal limit .
emergent brain ct showed diffuse subarachnoid hemorrhage ( sah ) in the basal cistern and acute hydrocephalus ( fig .
the hematoma was located in posterior fossa , especially in interpeduncular cistern and prepontine cistern .
the diffusion mri , which was done one year prior to the time of stroke , showed multiple cerebral infarctions on both cerebellum and body of corpus callosum ( fig .
with mr angiography , we could identify the fusiform aneurysms on the left sca and the left pica .
2b ) . the conventional angiography revealed multiple dissecting aneurysms in left sca , left pica and right pericallosal artery ( fig .
considering hematoma distribution , we concluded that the sca aneurysm was responsible for sah . since collateral circulation to midbrain
, pons and cerebellum was abundant , we decided to occlude left sca with coil embolization ( fig .
postoperative diffusion mri revealed cerebellar infarction ; however , the patient showed no clinical symptom and was able to discharge with alert mentality , recovered from hemiparesis after rehabilitation ( fig .
intracranial dissection is rare event comparing to extracranial dissection , and is usually demonstrate ischemic event of young adults when it 's symptomatic5,22 )
. it usually relates to exogenous triggers like trauma , infection as well as inherited connective tissue disorders .
our case was very rare one because it was a case of multiple intracranial dissecting aneurysms that resulted in sah as well as acute cerebral infarction which was related to no other risk factors except et .
essential thrombocythemia is characterized by a high platelet count , originating from a pluripotent stem cell and usually affects middle aged to elderly .
nearly half of the patients are asymptomatic while the other half has vascular occlusive or hemorrhagic event14 ) .
it is known to cause a prothrombic state10,17 ) , and there are reports that describe the relationship between et with cerebral ischemic event .
arboix et al.3 ) has reported several cases of large - vessel occlusion which resulted in ischemic stroke due to et .
bogousslavsky et al.6 ) has reported that the ischemic stroke attributed to et was found in 0.4% of cases in the lausanne stroke registry .
there have been reports of intrapetrous ica dissection of the patient with et9,12 ) , yet multiple intracrnial dissecting aneurysms of the patient with et has been rarely reported .
piepgras et al.20 ) has reported the case of distal middle cerebral artery dissecting aneurysm secondary to proximal artery dissection , however , in our case , we could not find any dissection or occlusion in proximal arteries .
et , by changing prothrombotic state , causes a disturbance of microcirculation of vasa vasorum and as a result , increases the vulnerability of the vessel walls10 ) .
however , this theory only explains the dissection of extracranial arteries that the vasa vasorum is usually distributed to and does not fit in our case7 ) .
et can induce endothelial damage by activating leukocyte and releasing the elastase and alkaline phosphatase that play a role of the pathogenesis of the prothrombic state8 ) .
the most characteristic structure of intracranial artery is internal elastic lamina . instead of lack of external elastic membrane , thinner adventitia , and fewer elastic fibers of media ,
in addition , the media and internal layer of intracranial artery is lack of vasa vasorum7 ) .
these changes occurs at the level of skull base in the carotid artery and at the 1 cm proximal to the dural perforation in vertebral artery27 ) . with the anatomical differences ,
there are pathological differences between dissecting aneurysm of extracranial and intracranial arteries . in the extracranial artery ,
dissection usually occurs between the media and adventitia or outer layer of the media11,13,23,28 ) . in extracranial artery dissection , for example
, cystic medial necrosis and degeneration of elastic tissue in the media is observed4,18 ) . in the intracranial artery ,
on the other hand , intramural hematoma is usually formed between internal elastic lamina and media1,15,16,28,29 ) .
when the dissection involves the subadventitia and rupture into the subarachnoid space , sah is presented2,21,24,26,29 ) .
 the etiologies of intracranial artery dissection are various , the exogenous as well as inherited connective tissue disorders . 
 we report on a patient who presented with diffuse subarachnoid hemorrhage who had been suffered from essential thrombocythemia . 
 he was diagnosed to multiple dissecting aneurysms of left superior cerebellar artery , left posterior inferior cerebellar artery and right pericallosal artery and treated with endovascular coil embolization . 