Intracranial Atherosclerosis: Pathophysiology, Diagnosis and Treatment

J. S. Kim, L. R. Caplan, K. S. Wong

• Publisher: S. Karger
• Year: 2016
• ISBN:
  9783318027594
• Topic: Medicina
• Subtopic: Cardiología

Intracranial atherosclerosis is a leading cause of stroke in Asians and Africans. As these ethnic groups account for more than 70% of the world's population, it is in fact the major cause of ischemic stroke worldwide. This timely book provides readers with up-to-date knowledge of intracranial atherosclerosis, covering vascular anatomy, pathology, epidemiology, stroke mechanisms and syndromes, diagnostic methods as well as treatment strategies such as antithrombotics, angioplasty/stenting and surgery. Furthermore, nonatherosclerotic intracranial arterial diseases like Moyamoya disease, dissection, vasculitis and other miscellaneous disorders are extensively discussed. Experts from both East and West present the latest findings from cutting-edge research and discuss controversial topics from different yet balanced points of view, allowing readers to form their own unbiased opinion on these issues. With this approach, the book serves as a useful and stimulating guide on the diagnosis and management of intracranial atherosclerosis for neurologists, neurosurgeons, neuroradiologists and vascular interventionists.

Kim JS, Caplan LR, Wong KS (eds): Intracranial Atherosclerosis: Pathophysiology, Diagnosis and Treatment.
Front Neurol Neurosci. Basel, Karger, 2016, vol 40, pp 179-203 (DOI: 10.1159/000448313)

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Non-Atherosclerotic Intracranial Arterial Diseases

Jong S. Kim^a · Louis R. Caplan^b

^aDepartment of Neurology, Asan Medical Center, University of Ulsan, Seoul, Republic of Korea; ^bDepartment of Neurology, Beth Israel Deaconess Medical Center, Boston, Mass., USA

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Abstract

Atherosclerosis is not the only cause of intracranial arterial disease. Arterial dissection, moyamoya disease, vascular inflammatory disease, vasospasm and immunologic disorders are important non-atherosclerotic intracranial arterial diseases. Identification of the correct etiology is important in establishing treatment strategies and assessing prognosis. Careful history taking and appropriate laboratory testing are essential. Although catheter angiography is the most important diagnostic tool to examine various intracranial arterial diseases, other diagnostic modalities such as CT angiography and MR angiography are nowadays widely used. High resolution vessel wall MRI also can assist in making the correct diagnosis as this can yield information regarding vessel wall pathology. Certain diseases such as infectious vasculopathies and moyamoya disease are more prevalent in certain parts of the world, and physicians practicing in these regions should be mindful of these disorders. In this chapter, these non-atherosclerotic intracranial arterial diseases are discussed. Moyamoya disease will be described in another chapter.

© 2016 S. Karger AG, Basel

Arterial Dissection

Cervicocerebral artery dissections account for 1-2% of all ischemic strokes [1-3], and 10-25% of ischemic strokes in young and middle-aged patients [4, 5]. According to population-based studies, the incidence of spontaneous arterial dissections was 1.7-3.0/100,000 in the internal carotid arteries (ICAs) and was 1.0-1.5/100,000 in the vertebral arteries (VAs) [1, 6, 7]. The prevalence is higher in men than in women [8, 9], and females are younger and more often have migraine and multiple dissections [8].

Cervicocerebral artery dissections can result from either primary intimal tear with secondary dissection into the media layer or primary intramedial hemorrhage. The intramural hematoma is located within the medial layer or near the intimal or adventitial layer. A subintimal dissection leads to luminal stenosis and obstruction, resulting in an ischemic event. A subadventitial dissection may cause aneurysmal formation (dissecting aneurysm) and, when intracranial, may cause subarachnoid hemorrhage (SAH).

Dissections are categorized as traumatic or spontaneous (non-traumatic). In patients with spontaneous dissections, minor trauma in the form of stretching of the neck still plays a causative role. Inherent conditions predisposing to spontaneous arterial dissections include fibromuscular dysplasia, cystic medial necrosis, α1 antitrypsin deficiency, Ehlers-Danlos syndrome type IV, Loeys-Dietz syndrome, Marfan's syndrome, autosomal dominant polycystic kidney disease, tuberous sclerosis, migraine, and hyperhomocysteinemia [3, 10]. Ultrastructural morphological aberrations of dermal connective tissue were found in more than half of patients with spontaneous cervical artery dissections [11].

Intracranial Arterial Dissection

Intracranial arterial dissections are known to be less frequent than extracranial dissections. In a retrospective analysis of 263 patients with spontaneous cervicocerebral artery dissections at the Mayo Clinic between 1970 and 1991, 33 (12.5%) had intracranial dissections [3]. Another study showed that among 67 patients with cervicocerebral artery dissections, 9 (13.4%) had intracranial dissections [12]. In a study including a series of 169 patients with 195 VA dissections, 21 dissections (11%) occurred intracranially [8].

The frequency of intracranial dissections may have been underestimated because the diagnosis of intracranial dissection is more difficult than that of the extracranial counterpart. Extensive evaluation, such as repeated MRA in suspected patients [13], and utilization of high resolution vessel wall MRI, that can identify dissection, flap, or mural hematoma more easily [14], will increase the likelihood of diagnosis of intracranial dissection [15]. With advanced imaging, a recent study on dissections causing ischemic stroke or transient ischemic attack (TIA) reported that intracranial arterial dissection is two times more common than extracranial arterial dissection [15]. The most frequent site was the intracranial VA (ICVA).

In contrast to the cervical arteries, the intracranial arteries lack external elastic lamina and have only a thin adventitial layer. Intracranial dissections more readily lead to the development of subadventitial dissections and dissecting aneurysm formation and SAH [16, 17]. Pathological studies have shown that subadventitial dissections are more frequent in the ICVA than in the middle cerebral artery (MCA) [18, 19]. This could explain the relatively high frequency of SAH in ICVA dissections as compared to dissections occurring in the MCA. Trauma, either serious or minor is more closely associated with extracranial dissections than intracranial dissections [3, 15, 17]. Extracranial vessels may be more susceptible to compression against bony structures after trauma, such as that caused by neck rotation. As in atherothrombotic infarction, extracranial dissection usually cause stroke or TIA via artery to artery embolism, whereas branch occlusion is an important stroke mechanism in intracranial dissections. Intracranial dissection frequently causes deep (subcortical and brainstem) infarction [20].

Clinical Manifestations

Dissection in the Anterior Circulation

In the anterior circulation, dissections most often occur in the supraclinoid ICA or the proximal MCA. Distal ICA dissection occasionally extends to the MCA (fig. 1). In a recent series, MCA dissection (19%) was the more prevalent than distal ICA dissection (12%) as a cause of ischemic stroke. In a review of 54 patients with MCA dissections who had 59, most presented with cerebral infarction (91%), while SAH was uncommon (9%) [21]. Most patients showed vascular luminal stenosis (87%), and a small number of patients had aneurysmal dilatation (11%) or a double lumen (2%). Hemiparesis was the most frequent presenting symptom (92%), followed by headache (61%) and consciousness change (44%). Preceding trauma was more often found in isolated MCA dissections than intracranial ICA-MCA dissections (35 vs. 19%). The exact mechanism of how a blunt head injury causes MCA dissection is not clear. One proffered suggestion is that the impact of the MCA against the sphenoid ridge causes an intimal tear, which results in dissection [22]. In contrast, congenital vessel wall defects were found more often in intracranial ICA-MCA dissections than in isolated MCA dissections (26 vs. 4%) [21].

Fig. 1. A 26-year-old woman developed mild (IV/V) right limb weakness. Diffusion weighted MRI (DWI) showed an acute, focal, left basal ganglia infarction (a). MR angiogram showed focal stenosis in the left terminal internal carotid artery (ICA) (b, arrow). Three days later, she developed aphasia and her limb weakness progressed to grade I/V. Follow-up DWI showed extension of the infarction that involved most of the left middle cerebral artery (MCA) territory (c). MR angiogram showed more severe ICA stenosis and poor visualization of the left MCA (d, arrow). 3D reconstruction of conventional angiography showed severe stenosis in the left distal ICA, and diffuse narrowing of the M1 portion of the MCA, which suggests extension of the dissection. Multiple stenoses of the M2 portion of the MCA suggest embolic occlusion (e, arrows). Source image of three-dimensional time-of-flight (TOF) MR angiography showed a flap like structure inside the distal ICA and proximal MCA (f, arrow).

Fig. 2. A 54-year-old man without vascular risk factors developed slight (IV/V) right leg weakness. Diffusion weighted MRI showed left anterior cerebral artery (ACA) territory infarction (a). MR angiography findings were normal (b). After admission, the leg weakness worsened progressively (II/V). Four days later, ...