27A. Ischemic stroke

Ischaemic stroke is the most common form of stroke, and accounts for 80% of stroke cases. It occurs due to anaemic infarction of the brain, but the underlying cause of the necrosis depends on the type of stroke.

We can differentiate six types according to etiology:

• Large artery stroke
• Small artery/lacunar stroke
• Embolic stroke
• Watershed stroke
• Cryptogenic stroke
• Stroke due to non-atherosclerotic vascular disease

Symptoms of anterior and posterior circulation stroke, evaluation, and treatment of stroke are discussed in other topics.

Large artery stroke

Large artery stroke is due to occlusion of large arteries supplying the brain, most commonly the middle cerebral artery but also the anterior or posterior cerebral artery, internal carotid artery, vertebral artery, etc. Large artery stroke is a CNS manifestation of cardiovascular disease and therefore occurs secondarily to atherosclerotic risk factors like hypertension, dyslipidaemia, etc.

The pathomechanism is similar as for myocardial infarction, with sudden rupture of an atherosclerotic plaque with resulting thrombosis. Large artery stroke has the worst prognosis, as it causes large infarcts (> 1,5 cm in diameter). Infarct can occur in both cortical and subcortical regions.

Small artery stroke

Small artery stroke, also called lacunar stroke, is due to occlusion of the so-called penetrating small arteries or lenticulostriate arteries. These are small arteries which arise at acute angles from larger arteries, which predispose them to turbulence in the context of hypertension. As such, small artery stroke is mostly related to hypertension. Chronic hypertension causes lipohyalinosis of these arteries, eventually causing occlusion.

These arteries are small in diameter and supply subcortical regions. As such, these strokes only affect subcortical structures and therefore don’t cause cortical symptoms like aphasia, and they only cause smaller strokes (< 1,5 cm). Lacunar strokes usually cause one of over 20 combinations of clinical features (syndromes). The most common are:

• Only hemiparesis
• Only hemisensory loss
• Hemiparesis + hemisensory loss
• Ataxic hemiparesis
• Dysarthria-clumsy hand syndrome (facial and hand weakness + dysarthria)

Embolic stroke

These strokes occur due to embolism, most commonly from the heart or carotid artery. For this reason, everyone with a stroke must be evaluated for sources of embolism. The most common sources are like atrial fibrillation (most common cause), myocardial infarction, endocarditis, or carotid artery stenosis.

These strokes usually affect the cortical surfaces. Multiple emboli may occur simultaneously, causing multiple strokes.

Watershed stroke

A watershed area is a part of the brain which is supplied by the distalmost branches of two separate arteries. If perfusion through one of these two arteries decreases, the watershed area can be safely supplied by the other artery. However, if the perfusion through both arteries decreases, the watershed area is unlikely to receive sufficient perfusion.

Watershed stroke refers to infarction of the watershed region which occurs when there is a sudden decrease in blood flow through both of these arteries. This is usually due to systemic hypoperfusion rather than single artery occlusion. This can occur due to cardiac arrest, severe hypotension, etc.

The clinical features depend on which watershed region is affected:

• Stroke in the ACA-MCA watershed region -> sensory loss and paresis in both upper arms, but spares the underarms and lower limbs – also called “man in a barrel” syndrome
• Stroke in the MCA-PCA watershed region -> visual loss

Cryptogenic stroke

In cases where the etiology initially cannot be determined, the stroke is called cryptogenic. The underlying etiology is usually paroxysmal atrial fibrillation, patent foramen ovale with paradoxical embolism, or non-atherosclerotic vasculopathy.

Stroke due to non-atherosclerotic vascular disease

Vascular diseases apart from atherosclerotic vascular disease can also cause ischaemic stroke. This is usually due to arterial dissection or vasculitis. The mechanism of ischaemic stroke is either development of thromboembolism or by abnormal haemodynamics.

Arterial dissection which causes stroke most commonly occurs in the internal carotid artery. This can cause stroke even in young people, and can be spontaneous or secondary to trauma.