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					                     Stroke

       Chih-Ping Chung, MD PHD
Department of Neurology, Taipei Veterans General Hospital
             National Yang Ming University
            腦中風 : 定義

• 腦中風 :
 快速發展之腦部功能局部或全面障礙, 症狀持
 續 24 小時以上,或造成死亡. 除了血管病變外,
 無其他明顯原因.


• 種類:
 – 阻塞性 (ischemic stroke)
 – 出血性 (hemorrhagic stroke)
CI: cerebral infarction
ICH: intracerebral hemorrhage
               Ischemic Stroke
•   Cerebral vessel anatomy and collaterals
•   Ischemic stroke classification (etiology-based)
•   Cerebral microvessel
•   Brain tissue ischemia
•   Management: increased cerebral blood flow
    (CBF)
Major Arteries supplying Brain:
   Anterior Circulation vs. Posterior Circulation
Anterior Circulation
Collateral circulation
Circle of Willis
Extracranial arterial collateral
         circulation
                • facial (a), maxillary (b),
                  and middle meningeal
                  (c) arteries to the
                  ophthalmic artery
                • dural arteriolar
                  anastomoses from the
                  middle meningeal
                  artery (d) and occipital
                  artery through the
                  mastoid foramen (e)
                  and parietal foramen (f)
    Intracranial arterial collateral
             circulation




• leptomeningeal anastomoses between anterior
  and middle cerebral arteries (b) and between
  posterior and middle cerebral arteries (c)
               Ischemic Stroke
•   Cerebral vessel anatomy and collaterals
•   Ischemic stroke classification (etiology-based)
•   Cerebral microvessel
•   Brain tissue ischemia
•   Management: increased cerebral blood flow
    (CBF)
      Etiologies of ischemic stroke
•   Large artery atherothromboembolism
•   Cardioembolism
•   Small vessel occlusion (Lacunar infarction)
•   Others
Atherosclerosis
      Etiologies of ischemic stroke
•   Large artery atherothromboembolism
•   Cardioembolism
•   Small vessel occlusion (Lacunar infarction)
•   Others
 High risk source of cardiogenic emboli
 History                 Cardiovascular evaluation

• Mechanical prosthetic heart      • Echo: dilated
  valve                              cardiomyopathy, atrial
• Af                                 myxoma, infective
• Sick sinus syndrome                endocarditis, akinetic left
                                     ventricular segment, left
• MI within 4 weeks                  atrial thrombus, left
• Dilated cardiomyopathy             ventricular thrombus
• Atrial myxoma                    • ECG: Af demonstrated at
• Infective endocarditis             any time during
• Akinetic left ventricular          hospitalization, AMI
  segment                          • Holter monitor: Af
• Left ventricular thrombus          demonstrated at any time
                                     during hospitalization, sick
                                     sinus syndrome
      Etiologies of ischemic stroke
•   Large artery atherothromboembolism
•   Cardioembolism
•   Small vessel occlusion (Lacunar infarction)
•   Others
             Small vessel disease
• 1965, CM Fisher – clinico-
  pathological studies of
  lacune (Fisher 1969, 1977,
  1978, 1979, Fisher and
  Caplan 1971, Fisher and
  Tapia 1987)
• He coined the term “lacune”:
  specific pathological and
  radiological presentations
            Small vessel disease
• Subcortical small
  infarction
• Long penetrating
  arterioles: from the pial
  network located on the
  surface of the brain
Perforating arteries
Perforating arteries
Small vessel disease: lacune
       Fisher’s theory: from the observations of
           parenchyma and vessel pathology

Lipohyalinosis & microatheroma




Microemboli
               Ischemic Stroke
•   Cerebral vessel anatomy and collaterals
•   Ischemic stroke classification (etiology-based)
•   Cerebral microvessel
•   Brain tissue ischemia
•   Management: increased cerebral blood flow
    (CBF)
                         Microvessels




• Arteriole: An arteriole is a small diameter blood vessel that
  extends and branches out from an artery and leads to capillary.




                                                                       Blood-brain barrier
  Thin muscular walls (usually only one to two layers of smooth
  muscle) and are the primary site of vascular resistance.
• Capillary: 5 – 10 um; composed of only a single layer of cell, the
  endothelium.
• Venule: A little vein. Venules go from capillaries to veins. Thin
  muscular walls
                        Capillary
• Enable the interchange of water, oxygen, carbon dioxide, and
  many other nutrient and waste chemical substances between
  blood and surrounding tissues.
• Perfusion pressure: the net pressure gradient causing blood
  flow to the brain. It must be maintained within narrow limits
  because too little pressure could cause brain tissue to become
  ischemic (having inadequate blood flow), and too much could
  raise intracranial pressure (ICP) or/and BBB damage and
  vasogenic edema.
• CPP = MAP − ICP (if ICP is higher than JVP)
                                 Or
  CPP = MAP − JVP (if JVP is higher than ICP).
• Cerebral blood flow (CBF) is driven by cerebral perfusion
  pressure (CPP)
            Microangiopathy
• Ischemia (perfusion pressure)
• Increased vascular permeability: BBB
  damage – vasogenic edema –
  IICP/hemorrhage
                  Arteriole:
            Cerebral autoregulation
• CBF is regulated by a complex system influenced by multiple
  factors: CPP, brain metabolic activity, autonomic innervation,
  vasodilators (CO2, NO), and drugs (acetazolamide)
• CA: The CBF is kept relatively constant within a wide range of
  the CPP.
• Endothelium and smooth muscle



                                        CPP = ABP – ICP (JVP)
Cerebral autoregulation is maintained by
different hypothesized control pathways
                    • Vasogenic
                    • Metabolic
                    Vasogenic mechanism
Intrinsic ability of cerebral vessels to responses to changes in transmural
pressure.




                                             Stroke 2003;34:1645-1649        Stroke
                                             1994;25:793-797          Stroke
                                             1995;26:1014-1019
                Vasogenic mechanism
                               Animal study

                                        • Intraluminal pressure:
                                          controlled by smooth muscle,
                                          modulated by endothelium
                                          (intracellular signals – Ca2+
                                          influx)
                                        • Flow: controlled by
                                          endothelium, mediated by
                                          NO
These counteracting mechanisms assure optimal adjustment of the
vessel diameter to CPP at any time.

   Circ Res 1995;77:832-840           Nuclear Medicine Review 2007;10:29-42 Circ Res
   1990;66:1445-1448          Stroke 1998;29:1194-1200
            Metabolic regulation
• Arteriolar resistance is
  modified by waste products
  of energy metabolism (CO2),
  partial pressure of O2, and
  release of specific
  vasoactive substances such
  as adenosine and potassium
  ions from neurons in
  response to insufficient
  blood supply.
                                Stroke 1977;8:358-360   Stroke
                                2002;33:844-849
Cerebral microvascular pathology

              HTN
              Aging
• Hyaline
  arteriosclerosis

• Lipohyalinosis



• Atherosclerosis

                                           Cerebral hypoperfusion (acute ischemia
Obstruction
                                           and chronic ischemia) in aging/HTN
Impaired autoregulation function           subjects


BBB damage            Vasogenic edema, microbleeding
Cerebral small vessel disease




       1. Lacunar infarction
     Cerebral small vessel disease




2. Leukoaraiosis (age-related white matter changes)
Leukoaraiosis
           • Risk factors:
             aging and HTN

           • Chronic cerebral
             hypoperfusion
             (decreased CBF
             globally)

           • BBB
    Vessel pathology in LA: fibrosis
• Hyaline arteriosclerosis: Degeneration of the media
  associated with depositions of collagens type I, III, IV, V, as
  well as other components of extracellular matrix in media and
  adventitia; increased amounts of basal lamina components
• Pericapillary sclerosis: the proliferation of collagen fibrils in
  the media and adventitia of the blood vessels is not specific to
  small arteries and arterioles but also occurred in the
  pericapillary spaces
• Capillary and arteriolar loss
• Venous collagenosis
               Ischemic Stroke
•   Cerebral vessel anatomy and collaterals
•   Ischemic stroke classification (etiology-based)
•   Cerebral microvessel
•   Brain tissue ischemia
•   Management: increased cerebral blood flow
    (CBF)
Brain tissue ischemia
               Ischemic Stroke
•   Cerebral vessel anatomy and collaterals
•   Ischemic stroke classification (etiology-based)
•   Cerebral microvessel
•   Brain tissue ischemia
•   Management: increased cerebral blood flow
    (CBF)
                      Management

 Cerebral arterial       Decreased CBF               Brain tissue
stenosis/occlusion       Cerebral autoregulation
                                                      ischemia
  LAA/CE/SVD/others     (endothelial function etc)




 • Improved CBF
 • Neuroprotection
Neuroprotection
        Management: improved CBF

 Cerebral arterial     Decreased CBF               Brain tissue
stenosis/occlusion     Cerebral autoregulation
                                                    ischemia
  LAA/CE/SVD/others   (endothelial function etc)



 • Prevention: endarterectomy, stenting
 • Acute management: thrombolytics – medical
   and mechanical
 • Targeting endothelial cell functions (ACEI,
   calcium blocker, statins, etc.)
          Take home messages
• Ischemic stroke is a heterogeneous disease
• Cerebral microvessel: specific structures and
  functions
• How to improve CBF

				
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posted:11/13/2011
language:Malay
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