Cerebral circulation | Anatomy2Medicine
cerebral-circulation

Cerebral circulation

 

  • Arteries of the Brain

 

      • supply 15% of the cardiac output to the brain.
      • provide the brain with 20% of the oxygen used by the body.
      • have a normal blood flow of 50 ml/100 g of brain tissue per minute.
      • consist of two pairs of vessels, the internal carotid arteries and the vertebral arteries, and their divisions.

 

  • At the junction between the medulla and the pons, the two vertebral arteries fuse to form the basilar artery.

 

        • Internal carotid artery

 

  • enters the cranium via the carotid canal of the temporal bone.

 

      • lies within the cavernous sinus as the carotid siphon.
      • supplies tributaries to the dura, hypophysis, tympanic cavity, and trigeminal ganglion.

 

  • provides direct branches to the optic nerve, optic chiasm, hypothalamus, and genu of the internal capsule.

 

      • Branches

 

  • Ophthalmic artery

 

          • enters the orbit via the optic canal with the optic nerve.

 

  • Central artery of the retina

 

          • is a branch of the ophthalmic artery.

 

  • provides the only blood supply to the inner five layers of the retina.

 

          • is an end artery; its occlusion results in blindness.

 

  • Posterior communicating artery

 

          • arises from the carotid siphon and joins the posterior cerebral artery.
          • supplies the optic chiasm and tract, hypothalamus, subthalamus, and anterior half of the ventral portion of the thalamus.

 

  • is a common site of berry aneurysms.
  • Anterior choroidal artery

 

          • arises from the internal carotid artery.

 

  • supplies the choroid plexus of the temporal horn of the lateral ventricle, hippocam-
  • pus, amygdala, optic tract, lateral geniculate body, globus pallidus, and ventral part of the posterior limb of the internal capsule.

 

          • supplies the proximal portion of optic radiations as they leave the lateral geniculate
          • body to form Meyer loop.

 

  • Anterior cerebral artery

 

          • originates at the terminal bifurcation of the internal carotid artery.

 

  • gives direct branches to the optic chiasm.

 

          • supplies the medial surface of the frontal and parietal lobes and corpus callosum. supplies part of the caudate nucleus and putamen and anterior limb of the internal capsule via the medial striate artery of Heubner
          • supplies the leg and foot area of the motor and sensory cortices (paracentral lobule)

 

  • Anterior communicating artery
  • connects the two anterior cerebral arteries.

 

          • is the most common site of berry aneurysms(MCQ)

 

  • Middle cerebral artery

 

          • begins at the bifurcation of the internal carotid artery.
          • supplies the lateral convexity of the hemisphere and underlying insula.

 

  • supplies the trunk, arm, and face areas of the motor and sensory cortices.

 

          • supplies the Broca and Wernicke speech areas.

 

  • supplies the caudate nucleus, putamen, globus pallidus, and anterior and posterior

 

          • limbs of the internal capsule via the lateral striate arteries.
    • Vertebral artery
      • is a branch of the subclavian artery.
      • joins its opposite partner to form the basilar artery.
      • gives rise to:

 

  • Anterior spinal artery
  • Posterior spinal artery
  • Posterior inferior cerebellar artery

 

          • gives rise to the posterior spinal artery.
          • supplies the dorsolateral zone of the medulla.

 

  • supplies the inferior surface of the cerebellum and the choroid plexus of the fourth ventricle.
  • supplies the medial and inferior vestibular nuclei, inferior cerebellar peduncle, nucleus ambiguus, intra-axial fibers of the glossopharyngeal nerve (CN IX) and the vagal nerve (CN X), spinothalamic tract, and spinal trigeminal nucleus and tract.
  • supplies the hypothalamospinal tract to the ciliospinal center of Budge at T1–T2 (Horner syndrome).

 

    • Basilar artery
      • is formed by the two vertebral arteries.
      • Branches

 

  • Pontine arteries

 

          • include penetrating and short circumferential branches.
          • supply corticospinal tracts and the intra-axial exiting fibers of the abducent nerve

 

  • Labyrinthine artery

 

          • arises from the basilar artery in 15% of the population.

 

  • perfuses the cochlea and the vestibular apparatus.
  • Anterior inferior cerebellar artery
  • supplies the inferior surface of the cerebellum.
  • supplies the facial nucleus and intra-axial fibers, spinal trigeminal nucleus and tract, vestibular nuclei, cochlear nuclei, intra-axial fibers of the vestibulocochlear nerve,spinothalamic tract, and inferior and middle cerebellar peduncles.

 

          • gives rise to the labyrinthine artery in 85% of the population.
          • supplies the hypothalamospinal tract (Horner syndrome).

 

  • Superior cerebellar artery
  • supplies the superior surface of the cerebellum and the cerebellar nuclei (dentate nucleus).
  • supplies the rostral and lateral pons, including the superior cerebellar peduncle and spinothalamic tract.
  • Posterior cerebral artery

 

          • originates from the internal carotid (fetal origin) in 20% of the population.

 

  • is formed by bifurcation of the basilar artery.
  • provides the major blood supply to the midbrain.
  • supplies the posterior half of the thalamus and the medial and lateral geniculate bodies.
  • supplies the occipital lobe, visual cortex, and inferior surface of the temporal lobe including the hippocampal formation.

 

          • gives rise to the lateral and medial posterior choroidal arteries, which supply the dorsal thalamus, pineal body, and choroid plexus of the third and lateral ventricles.

 

  • Arterial Circle of Willis

 

      • is formed by the anterior communicating, anterior cerebral, internal carotid, posterior communicating, and posterior cerebral arteries.
      • gives off penetrating arteries to supply the ventral diencephalon (hypothalamus, subthalamus, and thalamus) and the midbrain.

 

  • Meningeal Arteries

 

      • supply the intracranial dura.
      • usually arise from branches of the external carotid artery.
      • Anterior meningeal arteries
        • arise from the anterior and posterior ethmoidal arteries
        • supply the dura of the anterior cranial fossa.
      • Middle meningeal artery
        • is a branch of the maxillary artery.
        • enters the cranium via the foramen spinosum.
        • Laceration results in epidural hemorrhage (hematoma).
      • Posterior meningeal arteries
        • are branches of the ascending pharyngeal, vertebral, and occipital arteries.
        • supply the dura of the posterior cranial fossa.

 

  • Veins of the Brain

 

      • are devoid of valves
      • lie along surface sulci.
      • arise from the cortex and subcortical medullary substance
      • terminate in the dural sinuses.
      • Superficial cerebral veins
        • drain into the superior sagittal sinus (bridging veins).

 

  • Laceration of these vessels results in subdural hemorrhage (hematoma).

 

      • Deep cerebral veins

 

  • drain the deep subcortical structures of the cerebral hemispheres: septal area, thalamus, and basal ganglia.

 

        • Internal cerebral veins drain the following:

 

  • Septal vein
  • Thalamostriate vein
  • Terminal vein
  • Great vein of Galen (MCQ)

 

        • receives blood from the internal cerebral veins

 

  • drains into the straight sinus.
  • Venous Dural Sinuses

 

      • are endothelium-lined valveless channels
      • walls are formed by two layers of dura mater.
      • collect blood from the superficial and deep cerebral veins and the calvarium and represent the major drainage pathway of the cranial cavity.

 

  • receive arachnoid granulations and absorb cerebrospinal fluid (CSF).

 

      • Superior sagittal sinus
        • usually terminates in the right transverse sinus.

 

  • receives blood from the superficial cerebral veins, diploic veins, and parietal emissary veins.

 

        • receives arachnoid granulations and drains CSF from the subarachnoid space.
      • Inferior sagittal sinus
        • courses in the inferior edge of the falx cerebri.
        • joins the great cerebral vein to form the straight sinus.
      • Straight sinus
        • is formed by the great cerebral vein and the inferior sagittal sinus.
        • drains into the left transverse sinus.
        • drains the superior surface of the cerebellum.
      • Left and right transverse sinuses
        • originate at the confluence of the sinuses and course anterolaterally along the edge of the tentorium cerebelli to become the sigmoid sinus.
        • receive venous blood from the temporal and occipital lobes.
      • Confluence of the sinuses

 

  • is formed by the union of the superior sagittal, straight, and transverse sinuses.

 

      • Sigmoid sinus
        • is a continuation of the transverse sinus.
      • Sphenoparietal sinus
        • drains into the cavernous sinus.
      • Superior petrosal sinus

 

  • extends from the cavernous sinus to the sigmoid sinus.

 

      • receives tributaries from the pons, medulla, cerebellum, and inner ear.
    • Inferior petrosal sinus
      • drains into the jugular bulb.
      • receives major venous drainage from the inferior portion of the cerebellum.
      • drains the cavernous sinus and clival plexus into the internal jugular vein.
    • Cavernous sinus
      • surrounds the sella turcica and the body of the sphenoid bone.

 

  • contains, within the sinus, the internal carotid artery, sympathetic plexus, and abducent nerve (CN VI).
  • contains, within the lateral wall of the sinus, the oculomotor nerve (CN III), the trochlear nerve (CN IV), the ophthalmic nerve (CN V-1), and the maxillary branches (CN V-2) of the trigeminal nerve.

 

    • receives blood from the superior and the inferior ophthalmic veins.

Arterial supply of the Spinal Cord

    • Vertebral artery
      • is a branch of the subclavian artery.
      • gives rise to the anterior spinal artery and posterior spinal artery.

 

  • Anterior spinal artery

 

        • supplies the anterior two-thirds of the spinal cord, including the anterior and lateral horns.
        • supplies the pyramids, medial lemniscus, and intra-axial fibers of the hypoglossal nerve (cranial nerve [CN] XII) in the medulla.

 

  • Posterior spinal arteries

 

        • supply the posterior third of the spinal cord, including the posterior horns and columns.
        • supply the gracile and cuneate fasciculi and nuclei in the medulla.
      • Segmental arteries
        • arise from the aorta, vertebral arteries, and common iliac arteries as medullary arteries
        • provide the main blood supply to the spinal cord at thoracic and lumbar levels.

 

  • the artery of Adamkiewicz (MCQ)

 

          • second lumbar artery gives rise to a large anterior medullary artery

 

  • Its origin varies from T12 to L4, and it usually arises on the left side.

 

        • Segments T1 to T4 and L1 are poorly vascularized and are at risk.

 

  • Venous Drainage of the Spinal Cord
  • follows, in general, the arterial pattern.

 

    • passes from spinal veins within the subarachnoid space to the epidural internal venous plexus before draining into intracranial, cervical, thoracic, intercostal, or abdominal veins.
    • is conducted by valveless veins that permit bidirectional flow, depending on the existing pressure gradients.
    • is a pathway for transmission of infectious agents and tumor cells.

 

 

  • Intracranial Hemorrhage
  • Berry (saccular) aneurysms

 

          • develop at arterial bifurcations.

 

  • arterial circle of Willis contains 60%
  • 30% arise from the middle cerebral artery

 

          • remaining 10% are found in the vertebrobasilar system.

 

  • Pressure symptoms

 

            • of the anterior communicating artery frequently pressure the optic chiasm and cause a bitemporal lower quadrantanopia.
            • of the posterior communicating artery frequently cause a third nerve palsy.

 

  • Rupture is the most common cause of nontraumatic subarachnoid hemorrhage.
  • Microaneurysms (Charcot-Bouchard aneurysms)

 

      • are found in small arteries

 

  • most frequently within the territory of the middle cerebral artery (the lenticulostriate arteries).

 

      • Rupture occurs most frequently in the basal ganglia

 

  • the most common cause of nontraumatic intraparenchymal hemorrhage.

 

 

Subdural hemorrhage (hematoma)

  • results from rupture of the superior cerebral veins, the “bridging” veins that drain into the superior sagittal sinus.

Epidural hemorrhage (hematoma)

  • results from rupture of the middle meningeal artery, which lies between the dura and the inner table of the skull.