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Small vessel disease (Microangiopathy)

Introduction

Small vessel disease accounts for about 25% of the causes of Ischaemic stroke. It is also the main underlying pathology for deep bleeds which are discussed in the chapter on haemorrhagic stroke. It is closely associated with Hypertension. Small vessel disease is as its name suggests a disease predominately of the small penetrating arterioles usually less than 800 um in diameter. They often are found branching off sideways from small and medium sized arteries which come off the circle of Willis or vertebrobasilar systems. They cannot be imaged in vivo so we use surrogate markers - namely lacunar infarction and deep haemorrhages as evidence of its presence.

Important caveat is that small vessels disease can be due to large vessel disease such as proximal MCA embolic occlusion which may reperfuse after causing localised deep infarction or large plaques in larger vessel which can encroach on the ostia or branching small vessel causing occlusion. Multiple acute lacunar type infarcts may suggest embolism.

There may be some over exposure to high blood pressure as there is not the steady reduction in vessel calibre seen in other systems. The occlusion of these small vessels can lead to predominantly white matter damage and demyelination with axonal damage and scarring. In most cases a process called lipohyalinosis which seems different to atherosclerosis occludes the vessels. Other processes exits including amyloid and inherited genetic defects. An aetiological classification is shown below. The result is small deep hemispherical or brainstem (mainly pontine) strokes usually less than 15 mm in diameter. Hypertension and diabetes appear to be risk factors. This pattern of disease may also be seen with CADASIL, Fabry's disease, Vasculitis, migraine and other uncommon causes of stroke [Pantoni L 2010]. Don't forget that it is also disease of these small vessels that can lead to the classically deep haemorrhages that can be disabling or fatal.

Other rarer causes of small vessel strokes include localised radiotherapy, CADASIL, Fabry's disease. These will be discussed separately later.

Detailed classification of Small Vessel Disease [Pantoni L. 2010]

This classification and table need not need memorised but what is important is to realise that small vessel disease is mutifactorial with a broad differential and is in reality a number of pathological processes all affecting the small penetrating vessels.

Type and TitleDescription
1 : ArteriosclerosisCommonest form. Pathology shows Fibrinoid necrosis, Lipohyalinolysis, Microatheroma, Microaneurysms. Similar disease seen in kidney and retina. Associated with increasing age, diabetes and hypertension.
2 : Sporadic hereditary amyloidBeta A4 Amyloid deposition in walls of small and medium sized arteries and arterioles. May be blood extravasation. Associated with Alzheimer disease. Association with microbleeds on MRI. Unsure who gets microbleeds and others get large bleeds.
3 : Inherited/Genetic DefectsCADASIL, CARASIL, MELAS, Fabry's disease, Hereditary cerebroretinal vasculopathy, multi-infarct dementia of swedish type, COL4A1 mutations
4: Inflammatory/Immune (Vasculitis)Wegener's granulomatosis, Churg-Strauss, Microscopic polyangiitis, Henoch-Schoenlin, Cryoglobulinaemic vasculitis, Sneddon's syndrome, SLE, RA, Sjogren's syndrome
5 : Venous Collagenous
6 : other small vessel diseasePost radiation angiopathy

Clinically the effects are often subclinical but slightly larger occlusions can lead to lacunar infarcts which can certainly present with the classical lacunar syndromes discussed elsewhere. A more piecemeal damage can lead to a progressive vascular dementia, Gait apraxia and vascular parkinson's as deep white matter is affected as well as subcortical nuclei and their connections.

Lacunar syndromes

These are covered in more detail in clinical section are most often due to small vessel disease.

  • Pure motor
  • Pure Sensory
  • Sensory and motor
  • Ataxic hemiparesis
  • Dysarthria and clumsy hand
  • Hemichorea/hemiballismus

Learning objectives

  • Understand the aetiology and risk factors for Small vessel disease
  • Clinical syndromes caused and correlate with location
  • Discuss diagnostics and treatment strategies

Role of Imaging

Imaging is useful and CT often shows hypodensity most distinctly around the ventricles with associated cerebral atrophy. MRI is much more sensitive and shows increased signal on T2 and FLAIR. It is a very similar appearance and distribution to demyelination. Resulting lacunar infarcts are usually round and less than 1.5 cm in diameter. Diffusion weighted imaging is useful to pick these up acutely.

With Small vessel disease other MRI with gradient echo may show evidence of microbleeds showing the two sided nature of this disease. Doppler and Echo have probably less importance but should be done where indicated and where there is diagnostic doubt if this was a small vessel stroke or cardioembolism with a shower of small emboli occluding vessels.

Small Vessel Disease concentrated typically around the ventricles

Management

General management of small vessel disease is to first see if there is any suggestion of any of the more unlikely causes and test if there is especially in those under the age of 50 (Fabry's disease, CADASIL). However most of the time it is old age, hypertension and diabetes that seem to be the main risks. Manage any hypertension, diabetes and glycaemic control and most patients would be started on an antiplatelet and receive lipid reduction and smoking advice. The SPS3 trial has shown that there is no benefit in giving dual antiplatelet therapy (aspirin and clopidogrel) rather than aspirin alone in these patents [Benavente O 2011]. In the setting of acute stroke, those with small vessel disease should be considered for thrombolysis. The exact connection between small vessel stroke and larger vessel strokes is not fully understood. Carotid disease should also be addressed in those with symptomatic carotid disease and small vessel disease.


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