Intracranial Artery Dissection Research Articles

Improvement and Aggravation of Spontaneous Unruptured Vertebral Artery Dissection

Background: Intracranial vertebral artery dissection (VAD) is a well-recognized cause of stroke in young and middle-aged individuals, especially in Asian populations. However, a long-term natural course remains unclear. We investigated the long-term time course of VAD using imaging findings to examine the rate and predisposing factors for improvement. Methods: We registered 56 consecutive patients (40 males; mean age, 51.8 ± 10.7 years) with acute spontaneous VAD and retrospectively investigated neuroimaging and clinical course within 1 month and at 3 months ± 2 weeks, 6 months ± 2 weeks, and 12 months ± 2 weeks after onset to ascertain predisposing factors and time course for improvement. Results: The most common presenting symptoms were headache and/or posterior neck pain, seen in 41 patients (73%). Magnetic resonance imaging showed brainstem and/or cerebellum infarction in only 32 patients (57%). Of the 56 VADs, 16 (28%) presented with pearl and string sign, 5 (9%) with pearl sign, 15 (27%) with string sign, and 20 (36%) with occlusion sign. VAD occurred on the dominant side in 20 patients and on the nondominant side in the other 36 patients. The pearl and string sign was more frequently noted on the dominant side than on the nondominant side (50 vs. 17%, p = 0.008). On the other hand, occlusion occurred more often on the nondominant side than on the dominant side (47 vs. 15%, p = 0.016). Furthermore, the pearl and string sign was more frequently seen in the improvement group (41 vs. 15%, p = 0.028), whereas the occlusion sign was evident more frequently in the nonimprovement group (21 vs. 52%, p = 0.015). Follow-up neuroimaging evaluation was performed at 1 and 3 months in 91% each, and at 6 and 12 months in 82% each. VAD aggravation was identified within 1 month after onset in 14%, while VAD improvement was seen in 14, 38, 50, and 52% at each period, mainly within 6 months after onset. Older patients and current smoking were negatively associated with VAD improvement. Conclusions: VAD improvement primarily occurs within 6 months after onset, and VAD aggravation within 1 month. It seems that older patients and current smoking are negative predictors of VAD improvement as risk factors, and as image findings, the pearl and string sign is a positive predictor and occlusion a negative predictor.

Posttraumatic complications in pediatric skull fracture: dural sinus thrombosis, arterial dissection, and cerebrospinal fluid leakage.

OBJECTIVE Skull fracture is associated with several intracranial injuries. The object of this study was to determine the rate of fracture associated with venous thrombosis, intracranial arterial dissection (ICAD), and cerebrospinal fluid (CSF) leakage in pediatric patients. Further, the authors aimed to highlight the features of pediatric skull fracture that predict poor neurological outcomes. METHOD In this retrospective study, the authors evaluated the records of 258 pediatric patients who had incurred a traumatic skull fracture in the period from 2009 to 2015. All the patients had undergone CT imaging, which was used to characterize the type of skull fracture and other important features, including intracranial hemorrhage. Patients with fracture extending to a dural sinus or proximal to major intracranial vessels had undergone vascular imaging to evaluate for venous thrombosis or arterial dissection. Clinical data were also reviewed for patients who had CSF leakage. RESULTS Two hundred fifty-eight patients had 302 skull fractures, with 11.6% having multiple fractures. Falling was the most common mechanism of injury (52.3%), and the parietal bone was most frequently involved in the fracture (43.4%). Diastatic fracture was associated with increased intracranial hemorrhage (p < 0.05). The rate of venous thrombosis was 0.4%, and the rate of ICAD was also 0.4%. The rate of CSF leakage was 2.3%. Skull base fracture was the only significant risk factor associated with an increased risk of CSF leakage (p < 0.05). There was a significant difference in fracture-related morbidity in patients younger than versus older than 2 years of age. Patients younger than 2 years had fewer intracranial hemorrhages (21.8% vs 38.8%) and fewer neurosurgical interventions (3.0% vs 12.7%) than the patients older than 2 years (p < 0.001). Moreover, skull fracture in the younger group was mostly caused by falling (81.2% vs 33.1%); in the older group, fracture was most often caused by vehicle-related accidents (35.7% vs 4.0%) and being struck by or against an object (19.1% vs 7.9%). Additionally, skull fracture location was analyzed based on the mechanism of injury. Parietal bone fracture was closely associated with falling, and temporal bone fracture was associated with being struck by or against an object (p < 0.05). Frontal bone fracture was more associated with being struck by or against an object and vehicle-related injury (p < 0.05) than with falling. Vehicle-related accidents and being struck by or against an object, as opposed to falling, were associated with increased surgical intervention (13.3% vs 16.2% vs 3.7%, respectively). CONCLUSIONS Pediatric skull fracture usually has a benign outcome in patients who fall and are younger than 2 years of age. Poor prognostic factors include diastasis, an age > 2 years, and fracture caused by vehicle-related accidents or being struck by or against an object. In this series, the rates of venous thrombosis and ICAD were low, and the authors do not advocate vascular imaging unless these disease entities are clinically suspected. Patients with skull base fracture should be closely monitored for CSF leakage.

Thrombolytic therapy for acute ischemic stroke following intracranial artery dissection: Fukuoka stroke registry

Background: The use of thrombolytic therapy for acute ischemic stroke caused by intracranial artery dissection (IAD) remains controversial.

Usefulness of high-resolution magnetic resonance imaging with 3D T1 blood black sequence to identify intracranial artery dissection

Background: High-resolution magnetic resonance imaging involving 3D T1-weighted blood black sequence (HR-MRI) provides detail information about intracranial arteries and is useful to detect intracranial artery dissection (IAD). However, the diagnostic value of HR-MRI in addition to that of digital subtraction angiography (DSA) remains unclear.

Epidemiology and cerebrovascular events related to cervical and intracranial arteries dissection: the experience of the city of Pisa.

Spontaneous dissection of cervical arteries (sCAD) is a major cause of ischemic stroke in young patients, with an incidence varying from 1.7 to 3/100,000/year for extracranial internal carotid artery (ICAD) and 1 to 1.9/100,000/year for extracranial vertebral artery (VAD). Reliable epidemiological data on stroke incidence related to sCAD are scarce in Italy. This study aims to evaluate the incidence, clinical features, and outcome of cerebrovascular events related to sCAD and spontaneous intracranial arteries dissections (sIAD) in the city of Pisa (Italy). We retrospectively analyzed consecutive patients admitted between December 1997 and June 2015 with a diagnosis of stroke, TIA, or Bernard-Horner syndrome due to acute cervical or intracranial artery dissection. Considering that our hospital collects presumptively all patients hospitalized with sCAD coming from the referral geographical area, data may provide a good approximation to real incidence of sCAD in our population. Clinical and radiological features, acute treatment and outcome were collected. Seventy-seven cases were included (mean age 48.1±10.4years, range 23-77,72.7% males), 66 residents in the district of Pisa. Crude incidence rate of cerebrovascular events due to intra or extracranial dissection was 1.88/100,000/year. The incidence of ICAD was 0.80/100,000/year and 0.43/100,000/year for VAD. Stroke occurred in 76.6% of patients. VAD was more prone to cause ischemic stroke and present with cervical pain or focal signs (p<0.01) than ICAD group, which had older age at onset. sIAD were more frequent in the posterior circle (p=0.01) and more associated with ischemic lesions. A good outcome (mRS 0-2) was observed in 79% of patients. This is the first epidemiological attempt to investigate impact of sCAD and sIAD in Italy.

Complete ophthalmoplegia, complete ptosis and dilated pupil due to internal carotid artery dissection: as the first manifestation of Takayasu arteritis

BackgroundTakayasu arteritis is a rare, chronic large vessel vasculitis involving the aorta and its primary branches. As the disease progresses, the active inflammation of large vessels leads to dilation, narrowing and occlusion of the arteries. Arterial dissection is due to separation of the layers of the arterial wall resulting in a false lumen, where blood seeps into the vessel wall. Neurological sequelae of intracranial arterial dissection results from cerebral ischemia due to thromboembolism and hypo perfusion. Internal carotid artery dissection in Takayasu arteritis is very rare and complete ophthalmoplegia due to internal carotid artery dissection is also rare. This is the first case report of Takayasu arteritis presenting as complete ophthalmoplegia due to internal carotid artery dissection.Case presentationA 38-year-old Sri Lankan female presented with sudden onset severe headache, fixed dilated pupil, complete ptosis and ophthalmoplegia on the right side. On imaging, dissection and dilatation was evident in the right internal carotid artery from the origin up to the cavernous segment. She also had stenosis and aneurysmal dilatation of right subclavian artery. Takayasu arteritis was diagnosed subsequently. She was started on aspirin and high dose steroids.ConclusionsInternal carotid artery dissection within the cavernous sinus can lead to third, fourth and sixth nerve palsy due to compression, stretching and ischemia from occlusion of the nutritional arteries. This case report illustrates that internal carotid artery dissection should be a differential diagnosis in palsies of the third, fourth, or sixth cranial nerves, especially when associated with headache. In cases of internal carotid artery dissection, vasculitis such as Takayasu arteritis should also be considered.

Headache, TIA and subarachnoid haemorrhage: dissecting an unusual cause for stroke-like symptoms

We present a case of supraclinoid internal carotid artery dissection. Eleven months prior, the patient developed isolated periorbital pain and was diagnosed with giant-cell arteritis with iritis. The patient experienced...

Dissection of Cervical and Cerebral Arteries.

We aimed to summarize recent findings in cervical (CeAD) and intracranial artery dissection (IAD) research. Considered a disease of the young- and middle-aged, an analysis on the largest CeAD-population to date (n=2391) revealed that about 1 of 14 CeAD-patients was aged ≥60years. Distinct genetic variants were associated with CeAD. However, in clinical practice, genetic investigations are not helpful due to the small effect size. Despite the paucity of data from randomized-controlled trials in CeAD-stroke patients, both intravenous thrombolysis and endovascular treatment should be considered as acute treatment in such patients. Future research is needed to clarify which patients benefit most from each treatment modality. Whether to use antiplatelets or anticoagulants in stroke prevention in CeAD-patients is still a matter of debate. One randomized-controlled feasibility trial has been published, and another trial designed to show non-inferiority of aspirin to vitamin-K-antagonists is underway and will be terminated in late 2018. Non-vitamin-K-oral anticoagulants should not be used in CeAD outside a properly designed trial, as experience with these drugs in CeAD-patients is limited. With many IAD patients developing intracranial hemorrhage, antithrombotic therapy should be used with caution. Knowledge about CeAD and IAD has advanced substantially. Nevertheless, further research is mandatory, in particular regarding pathophysiology, acute treatment, and stroke-preventive therapy, as well as long-term outcome and prognosis.

Experimental determination of rupture pressure and stress of adventitia of human middle cerebral arteries.

Background Intracranial arterial dissections might be attributed to the particular biomechanical properties of their specific layers. Also, knowledge of adventitia properties would be crucial in the context of intracranial balloon angioplasty. Aims The purpose of this work was to determine the rupture pressure of separated adventitia and compare it to intact cerebral arterial segments. Methods Brain specimens were harvested from 14 autopsy subjects (age range from 23 to 86 years). Pressure-inflation tests were conducted on proximal segments of middle cerebral arteries and separated adventitia layers from contralateral arteries to assess the rupture pressure values. Results The averaged rupture pressure of adventitia layers was 1.41 SD 0.25 atm (1072 SD 190 mmHg), whereas for intact arterial segments it was 2.32 SD 0.70 atm (1763 SD 532 mmHg) and diminished with age according to nonlinear regression trends. The difference beetween the aformentioned rupture pressures was positively correlated with rupture pressure of intact arterial segments ( R2 = 0.88; p < 0.001). Conclusions The obtained experimental results indicate a leading role of adventitia in building arterial strength under supraphysiological pressure conditions. The greater the rupture pressure of complete cerebral arteries, the smaller the contribution of adventitia in overall wall resistance.

Middle cerebral artery dissection causing subarachnoid hemorrhage and cerebral infarction: Trapping with high-flow bypass preserving the lenticulostriate artery

Background:Spontaneous intracranial arterial dissection (IAD) is an increasingly important cause of stroke, such as subarachnoid hemorrhage (SAH) and hemodynamic or thromboembolic cerebral ischemia. IAD usually occurs in the posterior circulation, and is relatively rare in the anterior circulation including the middle cerebral artery (MCA). Various surgical and endovascular methods to reduce blood flow in the dissected lesion have been proposed, but no optimum treatment has been established.Case Description:An 80-year-old woman with dissection in the M1 portion of the MCA manifesting as SAH presented with repeated hemorrhage and cerebral infarction in the area of the inferior trunk of the MCA. High-flow bypass to the MCA was performed and the dissecting lesion was trapped. Prevention of repeated hemorrhage was achieved, and blood flow was preserved to the lenticulostriate artery as well as the MCA area distal to the lesion.Conclusions:Treatment strategy for IAD of the MCA should be planned for each patient and condition, and surgery should be performed promptly to prevent critical rebleeding given the high recurrence rate. In addition, preventing re-rupture of the IAD, and preserving important perforators around the lesion and blood flow distal to the dissection should be targeted by the treatment strategy.

Wingspan stentの使用経験と文献レビュー

We report three cases that involved the use of the Wingspan stent (WS) system for the treatment of intracranial atherosclerotic disease and review the literature. The first patient was an 80-year-old man who presented with recurrence of a transient ischemic attack and medically refractory restenosis of the left petrous internal carotid artery (ICA). He underwent percutaneous transluminal angioplasty (PTA) and stenting using the WS. There have been no ischemic events and no restenosis after treatment. The second patient was a 73-year-old man who presented with minor stroke due to chronic total occlusion of the left ICA. He underwent PTA and stenting using the WS for dissection of the left ICA. There have been no ischemic events and no restenosis after treatment. The third patient was a 65-year-old woman who presented with minor stroke due to stenosis of the right middle cerebral artery (MCA). She underwent PTA and stenting using the WS for dissection of the right MCA. There have been no ischemic events and no restenosis after treatment. The WS system was useful for the treatment of medically refractory restenosis and dissection of intracranial arteries after PTA.The 1-year risk of recurrence of ischemic stroke in the treatment of symptomatic intracranial arterial stenosis (ICAS) with the WS system was lower than that in the Warfarin-Aspirin Symptomatic Intracranial Disease (WASID) trial. However, the Stenting versus Aggressive Medical Therapy for Intracranial Arterial Stenosis (SAMMPRIS) trial demonstrated that aggressive medical treatment was superior to stenting with the WS system in preventing recurrent ischemic stroke. Further evaluation of clinical outcome is required to confirm the safety and efficacy of the WS system for symptomatic ICAS.

Two Cases of Intracranial Internal Carotid Artery Dissection Presenting with Ischemic Stroke

Two Cases of Intracranial Internal Carotid Artery Dissection Presenting with Ischemic Stroke

Simultaneous Onset of Ischemic and Hemorrhagic Stroke Due To Intracranial Artery Dissection

Intracranial dissections commonly present as ischemic stroke and as hemorrhagic stroke. In general, while either ischemic stroke or hemorrhagic stroke may develop, the simultaneous onset of both may also occasionally occur. In this report, we present a case of simultaneous development of ischemic stroke and hemorrhagic stroke due to an intracranial artery dissection.

Added Value of 3D Proton-Density Weighted Images in Diagnosis of Intracranial Arterial Dissection

BackgroundAn early and reliable diagnosis of intracranial arterial dissection is important to reduce the risk of neurological complication. The purpose of this study was to assess the clinical usefulness of three-dimensional high-resolution MRI (3D-HR-MRI) including pre- and post-contrast T1-weighted volumetric isotropic turbo spin echo acquisition with improved motion-sensitized driven equilibrium preparation (3D-iMSDE-T1) and proton-density weighted image (3D-PD) in detecting dissection and to evaluate the added value of 3D-PD in diagnosing intracranial arterial dissection.MethodsWe retrospectively recruited patients who underwent 3D-HR-MRI with clinical suspicion of arterial dissection. Among them, we selected patients who were diagnosed with definite dissection according to the Spontaneous Cervicocephalic Arterial Dissections Study criteria. For each patient, the presence of intimal flap, intramural hematoma, and vessel dilatation were evaluated independently by two neuroradiologists on each sequence. Interobserver agreement was assessed.ResultsSeventeen patients (mean age: 41 ± 10 [SD] years; 13 men) were diagnosed with definite dissection. The intimal flaps were more frequently detected on 3D-PD (88.2%, 15/17) than on 3D-iMSDE-T1 (29.4%, 5/17), and post-contrast 3D-iMSDE-T1 (35.3%, 6/17; P = 0.006 and P = 0.004, respectively). No significant difference was found in the detection rate of intramural hematomas (59–71%) and vascular dilatations (47%) on each sequence. Interobserver agreement for detection of dissection findings showed almost perfect agreement (k = 0.84–1.00), except for detection of intimal flaps on pre-contrast 3D-iMSDE-T1 (k = 0.62). After addition of 3D-PD to pre- and post-contrast 3D-iMSDE-T1, more patients were diagnosed with definite dissection with the initial MRI (88.2% vs. 47.1%; P = 0.039).ConclusionsThe intimal flap might be better visualized on the 3D-PD sequence than the 3D-iMSDE-T1 sequences, allowing diagnosis of definite dissection without follow-up imaging.

Cervical Arterial Fibromuscular Dysplasia in a Biethnic Population: A Retrospective Study in the U.S.-Mexican Border.

Background There have been studies trying to characterize Fibromuscular Dysplasia (FMD); however, most of them are based in mainly non-Hispanic sample. The objective of this study is to better understand the epidemiology and clinical characteristics of craniocervical FMD in the Hispanic population. Methods We retrospectively reviewed the cerebral angiograms performed in our center in a period of 3.5 years under any indication looking for angiographic patterns of FMD. Exclusion criteria consisted of cases in which the first angiogram was done when the patients were younger than 18 years. Patients were subdivided based on those with FMD and those without it for baseline characteristics and were looked for any associations. We further compared the same baseline characteristics among Hispanic FMD and non-Hispanic FMD population. A chart review was conducted looking for clinical features and vascular events. Results We analyzed 448 angiograms among patients younger than 18 years. We identified 47 patients with evidence of FMD involving the cervical arteries and 401 patients without FMD. Of the 47 patients with FMD in our neuroendovascular registry, we found that 76.6% were women and 57.4% were Hispanics. There was no statistical significant difference when comparing the variables across ethnicities, except history of cigarette smoking and dyslipidemia. The most common associated supra-aortic arterial lesions seen in the FMD group were intracranial aneurysm and arterial dissections. We then used same variables to compare Hispanic FMD with non-Hispanic FMD. We have found that there has been a positive association of cigarette smoking and dyslipidemia with FMD ( p ≤ 0.05). Conclusion Our study suggests that FMD affecting the carotid and vertebral arteries has similar demographic pattern across ethnicities in the United States. In Hispanics, the disease appears to have a predilection for women and history of cigarette smoking. Intracranial aneurysm and arterial dissection were the most commonly associated arterial lesions.

Spontaneous and Unruptured Chronic Intracranial Artery Dissection : High-resolution Magnetic Resonance Imaging Findings.

The aim of this article is to present high-resolution magnetic resonance imaging (HR-MRI) findings of chronic stage spontaneous and unruptured intracranial artery dissection (ICAD). From March 2012 to April 2016 a total of 29 patients (15 male and14 female, age range 37-68 years) with chronic stage spontaneous and unruptured ICAD (vertebral artery 27, posterior inferior cerebellar artery 1 and middle cerebral artery 1) were retrospectively enrolled. Patients underwent HR-MRI more than 2months (median interval 564 days, range 69-391 days) after symptom onset and were diagnosed at symptom onset or at the first imaging acquisition, which included luminal angiography and/or HR-MRI with clinical information. The HR-MRI findings were evaluated against those of luminal angiography on the basis of the lumen wall morphology, including thickening, contrast enhancement and residual dissection. The HR-MRI findings were classified into complete normalization (normal lumen and wall with or without mild enhancement, n= 6), complete normalization with minimal wall changes (focal wall thickening with enhancement but normal luminal angiography, n= 8), incomplete normalization (focal wall thickening with enhancement with dilatation and stenosis on luminal angiography, n= 4), dissecting aneurysm (fusiform aneurysm with residual dissection findings, n= 8) and occlusion (small outer arterial diameter with diffuse contrast enhancement, n= 3). The use of HR-MRI can demonstrate the distinguishing morphological features of chronic stage of spontaneous and unruptured ICAD as complete normalization, complete normalization with minimal wall changes, incomplete normalization, dissecting aneurysm and occlusion.

Diagnosis and follow-up of posterior inferior cerebellar artery dissection complicated with ischemic stroke assisted by T1-VISTA: a report of two cases

BackgroundVolume isotropic turbo spin-echo acquisition (VISTA) is a new method similar to the 3D black-blood imaging method that enables visualization of a intramural hematoma. T1-VISTA has recently been applied in the diagnosis of intracranial arterial dissection. However, the identification of an intramural hematoma in posterior inferior cerebellar dissection (PICA-D) by T1-VISTA has only rarely been reported.Case presentationWe herein report two patients who suffered from PICA-D complicated with ischemic stroke. Initial magnetic resonance arteriography was not informative, however, T1-VISTA depicted high-intensity signal areas suggesting an intramural hematoma of PICA-D in both cases. The high-intensity signal areas gradually reduced and finally disappeared at 4 months and 5 months after the onset, respectively.ConclusionOur cases demonstrate that T1-VISTA was able to assist in the diagnosis and follow-up of PICA-D.

Diagnosing intra-cranial and cervical artery dissection using MRI as the initial modality

Dissection of cranial and cervical arteries is a relatively frequent clinical condition. However, it is difficult to diagnose a dissection when patients present with relatively mild symptoms. Various radiological techniques are used as diagnostic tools. This study analyzed retrospectively the characteristics of cranial and cervical artery dissections using “MR first concept”, with MRI as the first-choice diagnostic modality for all new patients with neurological symptoms. The patients who were admitted in Ohnishi neurological center between January 2001 and December 2014 were included. MRI was used as the initial investigation for all new patients, including those with mild symptoms such as headache or vertigo only. The patients were divided into carotid group and vertebral group. The statistical comparison was performed between these two groups. A total of 164 patient cases were analyzed. In 44 (26.8%) and 120 (73.2%) patients, dissection occurred in the carotid group and vertebral group, respectively. Concerning the type of onset, 52 patients presented with only subjective symptoms accompanied with ischemic or hemorrhagic lesions, 97 patients with ischemic symptoms and 15 patients with subarachnoid hemorrhage. There were statistically significant differences between the carotid and vertebral groups in terms of hemiparesis, aphasia, history of trauma, headache and vertigo. Patients with only a headache and those with no ischemic features had no worsening symptoms. The symptom of headache or neck pain only is more frequent than previously reported. The “MR first concept” would prove useful for early diagnosis of dissections and early treatment.

Basilar artery dissection: A rare complication of posterior fossa epidermoid cyst resection, and evaluation of the possible effects of cerebrospinal fluid drainage on disease progression

We report a rare case of a 45-year-old female with an unruptured basilar artery dissecting aneurysm presenting with locked-in syndrome due to brainstem ischemia eleven months following resection of a giant cerebellopontine angle epidermoid cyst and three months after insertion of ventriculo peritoneal shunt due to hydrocephalus. The etiology of basilar artery dissection and the effect of hydrocephalus and ventricular cerebrospinal fluid drainage on disease progression in this patient are unclear. Our report suggests a possible effect of hydrocephalus and ventricular cerebrospinal fluid drainage on intracranial arterial dissection progression.

Selective Application of High-Resolution 3 T MRI in the Evaluation of Intracranial Vertebral Artery Dissection.

Although high-resolution magnetic resonance imaging (HR-MRI) is considered optimal for the diagnosis of intracranial vertebral artery dissection (IVAD), it is not readily available for all patients with suspected IVAD. The purpose of our study was to determine the factor related to IVAD lesions that are not definitively diagnosed by conventional MRI. This study included IVAD lesions that were evaluated with both of 3 T conventional MRI and HR-MRI. Definitive dissection was defined as the presence of one or more pathognomonic radiological findings including crescentic intramural hematoma, intimal flap, and double lumen. A total of 30 IVAD lesions definitively diagnosed by HR-MRI were included and grouped into a conventional MRI true-positive group (n = 17) or false-negative group (n = 13) based on the presence of definitive findings on conventional MRI. Clinical characteristics did not differ between the two groups. The absence of vertebral artery aneurysmal dilatation was more common in the conventional MRI false-negative group (84.6% vs. 35.3%; P = .010). Ipsilesional vertebral hypoplasia was observed more frequently in the conventional MRI false-negative IVAD group (53.8% vs. 17.6%; P = .056). In logistic regression, absence of vertebral artery aneurysmal dilatation was independently associated with conventional MRI false-negative IVAD (OR, 16.37; 95% CI, 1.39-192.30; P = .026). Ipsilesional vertebral artery hypoplasia showed only a trend as a predictor of conventional MRI false-negative IVAD (OR, 7.24; 95% CI, .73-71.51; P = 0.090). HR-MRI may be useful for diagnosing IVAD without aneurysmal dilatation or with ipsilesional vertebral hypoplasia.