Intracranial Arterial Stenosis

Raymond D. Turner IV, M. Imran Chaudry, and Aquilla S. Turk

Etiology

Intracranial stenosis is responsible for approximately 10% of all strokes. The most common etiologies for intracranial stenosis are intracranial atherosclerotic disease (ICAD) and intracranial vasculitides.1,2 ICAD often occurs in patients with widespread vasculopathy and is more common in the Asian, Hispanic and African American populations.^3–6 Increased age, hypertension, hyperlipidemia, smoking, and diabetes are also risk factors.^3–7 Intracranial vasculitides have a variety of causative factors.

Fibromuscular dysplasia (FMD) is an arteriopathy of medium and large arteries and can be unifocal or multifocal. The precise cause of FMD is unknown. Histological studies demonstrate that the dysplasia presents as intimal fibroplasia, medial fibroplasia, or adventitial hyperplasia.⁸ FMD is more common in women, which may be explained by a role of estrogen and progresterone or by an inheritable trait with poor penetrance in men.^9–11 Angiographically, FMD appears as irregularly spaced regions of constriction, having a “string of beads” appearance.⁸

Moyamoya disease is an intracranial occlusive disease that is more common in the Japanese population and involves stenosis and occlusion of the supraclinoid arteries. The etiology of moyamoya is unknown.¹² These occlusions result in poor cerebral perfusion and the development of arterial collaterals, most commonly located at the distal supraclinoid and proximal M1 and A1 segments. Angiographically, they resemble a “puff of smoke,” which is the English translation of the Japanese word moyamoya, first coined by Suzuki and Takaku.¹³ The early appearance of moyamoya can be easily mistaken for ICAD; however, moyamoya usually appears in a younger population (bimodal distribution: <10 years old and at the fourth decade) and can be bilateral. However, a subgroup of patients was discovered in the U.S. Wingspan registry who were younger than 55 years old with symptomatic supraclinoid internal carotid artery stenosis, due to their high propensity to develop recurrent stenosis (nearly 89%) despite stenting.¹⁴ These patients may represent either another form of the disease or simply be a part of the ongoing pathogenesis. A four-stage development of moyamoya disease, which incorporates the multitude of presentations, has been proposed and each should be taken into consideration in young people who present with intracranial stenosis (Table 18.1).

Table 18.1 Stages of Moyamoya Disease

Stage	Findings
I/II	1. Only mild stenosis of the carotid fork
	2. All main cerebral arteries dilated
III	Marked luminal narrowing in MCA and ACA
IV	Occlusion of the ICA to the posterior communicating artery
V	1. Occlusion of the ICA and the siphon region of the ICA
	2. Almost complete disappearance of all the main arteries from the internal carotid artery supply
VI	Complete disappearance of the ICA siphon region

Diagnosis

Clinical Presentations

It is important to understand the functional implications of vascular ischemia in any given arterial territory (Table 18.2, Table 18.3, and Table 18.4). For example, anterior cerebral artery ischemia would manifest with contralateral leg weakness as the most prominent symptom, whereas middle cerebral artery ischemia presents primarily with contralateral face and arm weakness, along with aphasia if it occurs in the dominant hemisphere. It is uncommon for anterior circulation stroke to present with cranial nerve palsies, such as peri-oral numbness, a sign of dysfunction in the chief sensory nucleus of cranial nerve V. It is important to note that it is not uncommon for patients with ICAD to present with a stuttering presentation of waxing and waning symptoms. Dominant hemisphere, anterior circulation stroke differs from the nondominant hemisphere stroke in the profound loss of language abilities (Table 18.3). Posterior circulation hypoperfusion typically presents with brainstem and cerebellar abnormalities, such as ataxia, vertigo, and cranial nerve findings (Table 18.4).

A comprehensive understanding of stroke physiology will not only assist in the diagnosis of an ischemic event (as opposed to other neurological causes of dysfunction, such as the post-ictal state of a seizure) but also in determining whether or not a given stenosis or occlusion can cause the patient’s current symptomatology.

Table 18.2 Non-Dominant Hemisphere Anterior Circulation Stroke Symptoms

Contralateral hemiparesis and sensory loss

Extinction to contralateral stimuli

Neglect of contralateral visual field

Poor contralateral conjugate gaze

Dysarthria

Spatial disorientation

Table 18.3 Dominant Hemisphere, Anterior Circulation Stroke Symptoms

Expressive aphasia, receptive aphasia, or both

Loss of language abilities

Alexia, agraphia, acalculia

Contralateral weakness, sensory loss, and visual field deficits

Table 18.4 Posterior Circulation Stroke Symptoms

Dizziness

Vertigo

Syncope

Cranial nerve palsies

Extremity weakness

Visual changes

Gait ataxia

Cerebellar dysfunction

Locked-in syndrome

Clinical Examination

Although a thorough medical history and physical examination are always important, a patient with acute neurological change must be triaged in a different manner than a patient who presents to your outpatient clinic with longstanding complaints.

• In the acute setting, it is critical to determine the onset of symptoms, a medication history (with close attention to antiplatelet and anticoagulation medications), and allergies; in addition, a focused neurological examination should be performed in concordance with the National Institutes of Health Stroke Scale (NIHSS).

• Once initial evaluation is completed, the patient should be taken for emergent imaging, with preference given to a non-contrast, non-spiral CT scan, CT angiogram (CTA), and CT perfusion (CTP), since these can typically be done more expeditiously than MRI at most institutions.

• At this point, the physician can determine whether or not the neurological decline is related to a stroke or not, as well as whether the stroke is secondary to an occlusion or a stenosis.

• A decision must then be made of whether or not to implement emergency stroke therapy.

• Once that decision point is reached, the remainder of the history must be obtained, a review of systems completed, past medical and surgical history obtained, and a thorough physical and neurological examination performed by the physician or mid-level provider.

• It is important to emphasize that in the acute setting, it is impossible to determine whether the acute decline in neurological status will require emergency intervention until the focused history, neurological exam, and imaging have been completed.

The American Stroke Association recommends that the target time from presentation to CT scan should be within 25 minutes, which justifies the need for a more focused triage approach up front.15

Diagnostic Imaging Studies

• Computed tomography (CT) is the first line of imaging.

• CT is widely available and faster than magnetic resonance (MR) imaging, while also being less expensive. However, there may be issues with contrast and radiation exposure.

• Non-contrast CT can provide information related to the presence or absence of early infarct signs (for example, hypodensity, loss of insular ribbon) as well whether or not the patient’s deficits are related to a hemorrhagic stroke.

• Most centers are able to provide CT angiography and CT perfusion data.

▪ CT angiography provides images of the intracranial and extracranial vasculature.

▪ CT perfusion evaluates blood flow, volume, and mean transit time to identify territories of decreased perfusion. Diamox imaging can test a patient’s reserve or ability to provide additional blood flow to a territory that has been vasodilated.

• An alternative to CT is single photon emission computed tomography (SPECT), which allows for a better evaluation of the posterior circulation and does not require contrast.

• MR imaging

• Although MR is a superior imaging modality that provides better sensitivity and specificity for stroke along with improved imaging of the surrounding tissues and requires no iodinated contrast agents or radiation, it is more costly, less available, and requires more time for image acquisition.

• Positron emission tomography (PET) evaluations of oxygen extraction fractions are useful in determining areas of hypoperfusion and at risk of stroke; however, PET imaging is expensive and has very limited availability.

Grading Systems

Several grading systems have been developed to measure the severity of intracranial arterial stenosis. However, the two most commonly used systems were developed to measure extracranial carotid artery stenosis in the the following studies: (1) the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and (2) the European Carotid Surgery Trial (ECST).

The warfarin-aspirin symptomatic intracranial disease (WASID) grading scheme (Fig. 18.1

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