Thrombotic Embolic

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Clinical Differentiation Between Thrombotic and Embolic Stroke
This learning objective discusses how to clinical differentiate between a thrombotic versus an embolic stroke. This distinction is important as it provides valuable information on the potential etiology of stroke and can help guide the diagnostic workup and management of a patient. A thrombotic stroke occurs when a clot forms at the site of a diseased blood vessel, due to pathological factors related to the vessel. The underlying process is usually atherosclerosis and associated chronic inflammation. Eventually a critical point is reached where the plaque may rupture and triggers a inflammatory cascade that recruits platelets and subsequent fibrin formation within the lumen of a vessel. The result is disruption of blood flow to the brain supplied distally by the vessel, and a subsequent stroke.

Unstable Fibrous Atherosclerotic Plaque Above: Rupture of the fibrous cap or ulceration of the fibrous plaque can rapidly lead to thrombosis and usually occurs at sites of thinning of the fibrous cap that covers the advanced lesion. Thinning of the fibrous cap is apparently due to the continuing influx and activation of macrophages, which release metalloproteinases and other proteolytic enzymes at these sites. These enzymes cause degradation of the matrix, which can lead to hemorrhage from the vasa vasorum or from the lumen of the artery and can result in thrombus formation and occlusion of the artery. Adapted from: Ross, R, Atherosclerosis — An Inflammatory Disease, NEJM, Volume 340:115-126, Figure 4, January 14, 1999.

Above: Common locations for thrombosis. Thrombosis most commonly occurs at sites of arterial atherosclerosis, typically at the origin and bifurcation of vessels. The red circles indicate the most common sites. The blue circles (intracranial MCA, ACA and PCA) are uncommonly affected except in the Asian and African American populations. Adapted from Caplan, Caplan's Stroke: A Clinical Approach, Third Edition, 2000. MCA = middle cerebral artery; ACA = anterior cerebral artery; PCA = posterior cerebral artery; ICA = internal carotid artery; CCA = common carotid artery.
An embolic stroke occurs when a clot formed in a proximal site in the vasculature, moves downstream and lodges in a relatively random blood vessel and infarcting brain tissue. Note that an embolus usually lodges in a previously normal blood vessel, whereas a thrombus occurs in a diseased vessel.
Common Sources of Emboli Emboi most commonly orginate from the heart (a); aorta (b) or proximal arteries (c); the latter known as artery-to-artery embolus. The embolus then travels downstream and often occludes the anterior cerebral, middle cerebral or posterior artery, or branch of one those arteries. Note: embolic infarction are often wedged shaped (blue area). Adapted from Caplan, Caplan's Stroke: A Clinical Approach, Third Edition, 2000.

The following table lists general rules that help distinguish thrombotic versus embolic strokes. Please keep in mind that many exceptions occur.
	THROMBOTIC	EMBOLIC
Risk Factors:	Hypertension Hyperlipidemia Diabetes Mellitus Smoking Obesity Other systemic atherosclerosis Hypercoagulable states	Atrial fibrillation Hypercoagulable states Endocarditis Dilated cardiomyopathy Recent MI Akinetic Heart segment Prosthetic heart valve Rheumatic heart disease PFO / ASD
Etiologies:	Large vessel: Atherosclerosis Small penetrating arteries: Lipohylanosis Rarely (vasculitis, dissection, hypercoagulable states)	Cardiac source Artery-to-artery embolus Right-Left Cardiac or Pulmonary Shunt
Clinical presentation:	TIA symptoms frequent and occur in same distribution Symptoms may progress over minutes to hours Symptoms may wax and wane May occur during sleep and noticed on waking. Associated seizures rare	TIAs may occur in different distributions Maximal deficits at onset Occurs anytime of day or night May occur during vigorous activity Seizures more likely associated
Physical exam:	May have cortical or subcortical findings May have a classic lacunar syndrome	Usually has cortical findings
Distributions:	Most Common: Internal carotid artery Origin of the vertebral artery from the subclavian Intracranial vertebral Proximal and mid-basilar Small penetrating arteries (e.g., lenticulostriates of MCA and thalmoperforators from the proximal PCA) MCA, PCA, ACA intracranial stenosis (uncommon except in Asian and African American population)	Most Common: MCA (stem or cortical branch) PCA (stem or cortical branch) ACA (stem or cortical branch) Top of the Basilar Lacunar syndrome uncommon Rarely (PICA, AICA or SCA)
Acute Treatment:	Possible thrombolysis	Possible thrombolysis
Chronic Treatment:	Usually antiplatelets Possible carotid endartectomy for ICA high grade stenosis Possible stenting (if accessible) Risk factor modification	Often anticoagulation with warfarin for definite cardioembolic source Antiplatelets, if no definite embolic source discovered or if contraindicated Surgical correction of PFO / ASD (selected cases)

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