Welcome to Stroke Education.CO.UK

Learning objectives

  • Concepts such as anterior vs posterior circulation
  • Ensure knowledge of normal anatomy to the point of drawing it
  • Know the important variations and implications
  • Correlate anatomy and clinical findings and aetiology

    Vascular Anatomy

  • Left atrium → Left ventricle → Aorta → Aortic arch and its branches
    • Innominate artery
      • Right common carotid → Right internal carotid 2/3rds of supply
      • Right subclavian atery → Right Vertebral artery 1/3rd of supply
    • Left common carotid
      • Left internal carotid 2/3rds of supply
      • Left external carotid - does not supply brain except through collaterals
    • Left subclavian → Left Vertebral artery → Basilar artery → Posterior cerebral artery
  • Almost all arteries are paired except for the basilar artery and the anterior communicating
  • A patent foramen ovale or ASD or any right to left shunt can allow clot to pass from the deep veins of the legs to the left atrium and then into the systemic circulation
  • Anterior circulation

  • Internal Carotid artery
    • Cervical segment - within the neck. Associated with sympathetic supply.
    • Petrous segment - enters skull via foramen lacerum and runs forwards
    • Cavernous segment - enters the cavernous sinus and runs with th VIth nerve and gives off branch superior hypophysial to the posterior pituitary 
    • Supraclinoid segment - pierces dura and then splits into anterior cerebral artery and  middle cerebral artery
    • Ophthalmic artery 
      • First branch of the ICA and enters the orbit with the optic nerve and gives off a branch the central artery to retina. The artery runs forward to supply the eye and scalp around the eye as well as frontal and ethmoidal sinuses. Maxillary artery anastomoses provides some collateral flow if proximal occlusion. Occlusion of the ophthalmic artery does not tend to cause blindness and as there are collaterals
      • Branches
        • Central artery to the retina: runs along the centre of the optic nerve entering the eye to supply the inner retinal layers. Occlusion will cause monocular blindness
        • Posterior ciliary artery is the main source of blood supply to the optic nerve head (ONH), and it also supplies the choroid up to the equator, the retinal pigment epithelium. The blood supply in the ONH is segmental, so that most of its ischemic lesions result in sectoral visual field defects. There may be multiple (up to 5) PCAs. Vessel involved in Anterior Ischaemic optic neuropathy and Giant cell arteritis.
    • Posterior communicating artery (PCOMM)
      • Joins anterior and posterior circulations
      • Closely associated with IIIrd nerve which can be compressed by an aneurysm of the PCOMM
      • Irrigates the ventral thalamus, hypothalamus and tail of caudate
    • Anterior choroidal artery
      • Arises from the ICA and Passes posteriorly with branches to supply
        • Posterior limb of internal capsule
        • choroid plexus of lateral ventricle
        • optic tract and lateral geniculate body (hemianopia)
        • area of midbrain and globus pallidus and substantia nigra
    • Anterior cerebral artery (Medial surface of cerebrum. Arches up and around and back over the corpus callosum)
      • A1 Segment - from the bifurcation of the internal carotid to the anterior comm artery. Branches include 
        • Medial lenticulostriate artery : contributes to anteroinferior part including the anterior limb of internal capsule and anterior portion of caudate and putamen
        • Anterior communicating artery connects both ACA and is a common site of aneurysms
        • Recurrent artery of Heubner supplies head of caudate and  anteroinferior internal capsule
      • A2 Pericallosal branch - is the continuation of A1 supplying medial surface of cerebral cortex and corpus callosum after the Anterior communicating branch
        • Orbitofrontal
        • Polar frontal
        • Callosomarginal
    • Middle cerebral artery
      • M1 segment from the bifurcation of the internal carotid passes laterally to the surface of the insula where it bifurcates.
        • Occlusion here may result in massive infarction depending on collateral supply and whether it is proximal or distal to lenticulostriate vessels.
        • A clot may be seen in the artery "the hyperdense MCA sign" in which a string of thrombus may be seen within the M1 on Non contrast CT
        • Lateral lenticulostriate arteries (Deep penetrating vessels)
          • Branch of at right angles to supply the Globus pallidus and putamen, posterior limb of internal capsule, head and tail of caudate, thalamus and Meyer's loop which includes some of the optic radiations can be caught
          • Arterial occlusion typically may cause lacunar type strokes and vulnerable to lipohyalinosis and occlusion
        • M2 segment within the sylvian fissure and branch. A clot here may result in a "dot"sign on CT. The artery branches into 
          • M3 segments Upper division
            • prefrontal (frontal cortex)
            • precentral (primary motor and associated areas)
            • central (pre/post central gyri) 
            • post central (primary sensory area)
            • parietal (posterior parietal)
          • M3 segments Lower division
            • middle temporal (mid temporal cortex)
            • tempeoroccipitalroccipital (temporal and occipital cortex)
            • angular (angular and associated gyri)
            • R/L Subclavian artery

    Posterior circulation - Vertebrobasilar system

    • Vertebral artery - 1st branches of the subclavian arteries on either side then enter the transverse process at (C6) and ascends through the foramina in the transverse processes of the upper six cervical vertebrae to C1 where they enter the foramen magnum in front of the the medulla. Inside the the skull, the two vertebral arteries join to form the basilar artery.
      • Posterior inferior cerebellar artery
        • Largest branch of the vertebral and supplies lateral medulla and lateral cerebellum
        • Loops around medulla to the inferior surface of cerebellum.
        • Occlusion can cause Wallenburg's/Lateral Medullary syndrome
        • Infarction of Inferior cerebellum, IX,X,XI, Nucleus ambiguus
      • Anterior spinal artery (ventral medulla)
        • Forms at the point where the vertebral arteries fuse
      • Posterior spinal artery (dorsal medulla)
    • Basilar artery forms at the lower border of the pons by fusion fo the two vertebral arteries
      • Anterior inferior cerebellar artery supplies lateral pons and anteroinferior cerebellum
      • Superior cerebellar artery - supplies lateral pons and superior surface of cerebellum
      • 12 Pontine arteries penetrate to supply medial pons - are a number of small vessels which come off at right angles from either side of the basilar artery and supply the pons and adjacent parts of the brain
      • Internal auditory artery - a long slender branch, arises from near the middle of the artery; it accompanies the acoustic nerve through the internal acoustic meatus, and is distributed to the internal ear
    • Posterior cerebral artery (PCA)(embryologically originate from Internal carotid) passes laterally and is joined by the posterior communicating and then sweeps back around the cerebral peduncle to reach the tentorial surface of the occipital lobe.  
      • Postero-medial ganglionic branches arise at the commencement of the posterior cerebral artery and with branches from the post comm artery pierce the posterior perforated substance, and supply the medial surfaces of the thalami and the walls of the third ventricle.
      • Posterior choroidal branches run forward beneath the splenium of the corpus callosum, and supply the tela choroidea of the third ventricle and the choroid plexus
      • Postero-lateral ganglionic branches are small arteries which arise from the posterior cerebral artery after it has turned around the cerebral peduncle; they supply a considerable portion of the thalamus
      • Anterior temporal supplies uncus and the anterior part of the fusiform gyrus
      • Posterior temporal supplies inferior temporal gyri, calcarine, to the cuneus and gyrus lingualis and the back part of the convex surface of the occipital lobe
      • Parietooccipital to the cuneus and the precuneus.
  • Venous anatomy

    • Superior sagittal sinus: Venous blood from the brain passes across the subdural space in the bridging veins and emissary veins into the superior sagittal sinus. The sinus also receives CSF through the arachnoid villi.
    • Cavernous sinus: contains various other structures including III, IV and V1, V2 and VI and postganglionic sympathetic fibres and the siphon part of the internal carotid artery
    • Great cerebral vein drains deep cerebral structures into the Straight sinus
    • Ultimately all venous outflow is to the internal jugular vein

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