in most cases , subdural hematomas ( sdhs ) are caused by head trauma.7)33 ) spontaneous sdh is an uncommon condition , found in only 2.6% of acute subdural hematoma ( asdh ) cases . underlying etiologies for spontaneous sdh include ruptured aneurysms with or without concomitant subarachnoid hemorrhage ( sah ) , arteriovenous malformations , meningiomas , dural metastatic diseases , and hematologic or solid neoplasm.7 ) spontaneous pure asdh without concomitant sah due to the rupture of a cerebral aneurysm is extremely rare and only 40 cases were reported between 1981 and 2012.9)23)35 ) we report a case of spontaneous asdh without evidence of sah caused by a ruptured aneurysm at the middle cerebral artery ( mca ) bifurcation , presenting with repeated sentinel headaches . a 42-year - old woman was admitted to our institution with a history of sudden onset headache without any accompanying neurological deficit . a week prior to admission , the patient experienced two episodes of transient headache , each lasting a few hours . she had noted occasional headaches over the last few years ; however , they did not last more than a few minutes and were not severe . the initial computed tomography ( ct ) scan of the brain revealed an asdh without evidence of any other type of hemorrhage including sah ( fig . 1 ) , and laboratory studies , including coagulopathy screening , showed no abnormalities . for further evaluation , magnetic resonance angiography ( mra ) and subsequent conventional cerebral angiography were conducted , revealing a right middle cerebral artery bifurcation aneurysm ( fig . a right pterional approach was used as usual , but when a semi - lunar shaped dural incision was made , only a dark bloody sdh without sah was noted . there was no discoloration of brain parenchyma ; no hematoma was observed in the subarachnoid space . after total removal of the sdh , sylvian fissure dissection was performed and the aneurysm was identified at the middle cerebral artery bifurcation . the aneurysmal dome extended antero - inferiorly and laterally and was tightly adherent to the arachnoid membrane ( fig . the patient 's hospitalization was uneventful and a follow - up three - dimensional ct angiography performed 1 year after the operation showed no remnant or recurrent aneurysm ( fig . the mechanism of asdh caused by rupture of an intracranial aneurysm is different from that of asdh caused by trauma and tearing of cortical and bridging veins.10 ) according to previous studies , various mechanisms have been suggested to explain the occurrence of asdh without sah after aneurysm rupture . first , previous repeated minor ruptures of the aneurysm occur , causing small bleeds and the formation of tight adhesions between the aneurysm and the neighboring arachnoid membrane . eventually , massive bleeding fills the subdural space directly after a major rupture occurs.8)16)23)25 ) second , massive high - pressure bleeding causes laceration of the arachnoid membrane with bleeding into the subdural space.8)14)15)16)18 ) third , the rupture of a subdural carotid artery aneurysm results in a pure asdh.12)15)24 ) fourth , the cavernous sinus wall is eroded by the acute enlargement of an intracavernous aneurysm after thrombosis , leading to pure asdh.18)35 ) in the present case , intraoperative findings revealed a tight adhesion between the aneurysmal dome and the arachnoid membrane . the patient reported recurrent episodes of sentinel headache , suggesting that repeated small bleedings led to formation of the tight adhesion . , we analyzed 41 cases reported with pure asdh caused by the rupture of an intracranial aneurysm and have summarized them in table 1 . of these , 10 were caused by the rupture of an mca aneurysm , including the present case . in those cases , asdh was located at the convexity in seven cases , at both the tentorium and convexity in two cases ( including the present case ) , and at the anterior fossa in one case . six of these 10 cases underwent hematoma evacuation and clipping , as in the present case , and two cases underwent clipping only . in one case , surgery could not be performed , and in another case , treatment was not described . these 10 cases presented with a variety of symptoms and signs and experienced different outcomes . four cases were comatose at admission , and , in these patients , the final outcomes were poor ; two patients died and the other two patients were disabled . the other six cases presented with an alert to confused mental status with headache and/or other minor neurological deficits ; in four cases , the final outcomes were reported to be good , and there was no description of outcome in the other two cases . among all 41 cases analyzed , 17 patients presented with a semi - comatose to comatose mental status on admission , and only five of these patients ( 29% ) had good outcomes . six patients died and another six patients were disabled . the remaining 24 cases with a relatively good neurological status had generally good outcomes . excluding two cases without outcome description , 91% ( 20/22 patients ) had good outcomes , one patient died , and one patient remained comatose . based on these results , it appears that a favorable neurological status at admission is a predictive factor for a good outcome . these findings are consistent with those of schuss et al . who studied patients with asdh and sah , and concluded that a good neurological status at admission is a predictive factor for a good outcome.32 ) the rupture of an intracranial aneurysm may be the cause of a pure asdh in patients without a history of trauma , but this is often mistakenly ruled out because of the absence of sah . subsequently , determining the correct cause and providing the proper treatments in these patients may be delayed . therefore , when a patient presents with a pure sdh without a history of trauma or coagulopathy , imaging studies , such as three - dimensional ct angiography or mra , should be performed to evaluate for vascular lesions to determine the underlying cause and to guide optimal treatment for the patient .
pure subdural hematomas caused by a ruptured intracranial aneurysm are extremely rare . 
 we describe the case of a 42-year - old woman who presented with headache without evidence of head trauma . 
 magnetic resonance angiography and conventional cerebral angiography revealed a ruptured aneurysm at the right middle cerebral artery bifurcation . 
 the patient underwent surgical treatment and had a good outcome without any neurological deficit . 
 the mechanisms and clinical characteristics of this condition are discussed .