Blood supply of brain

• The brain accounts for about 2.5% of body weight, and receives about one sixth of the cardiac output. It accounts for one fifth of the oxygen consumed by the body at rest, and is supplied from branches of the vertebral and internal carotid arteries - circle of willis.
• The internal carotid artery arises from the common carotid artery in the neck. It enters the middle cranial cavity through the internal carotid foramen and carotid canal with characteristic bends called carotid syphon.
• Cervical part of internal carotid artery

  • extends vertically in the neck from origin to the base of the cranium
  • has no branch in the neck
• Petrous part of internal carotid artery

  • lies within carotid canal in petrous part of temporal bone
• Cavernous part of internal carotid artery

  • lies within cavernous sinus in carotid groove on body of sphenoid bone
• Cerebral part of internal carotid artery

  • joins cerebral arterial circle of Willis
• Vertebral artery

  • arises from subclavian artery
  • ascends through foramen transversaria from the level of the 6th cervical vertebrae
  • enters cranial cavity through foramen magnum
  • has no branch in neck
  • unites at junction of medulla and pons to form midline basilar artery
• Parts of vertebral artery

  • preforaminal or prevertebral (V1)
  • foraminal or vertebral (V2)
  • atlantal or suboccipital (V3)
  • intracranial (V4)
• The vertebral artery forms part of the circle of Willis in the cranial cavity that supply the brain
• Basilar artery gives rise to

  • superior cerebellar arteries (left and right)
  • posterior cerebral arteries (left and right)
• Internal carotid arteries give rise to:

  • posterior communicating arteries, join respective posterior cerebral arteries
  • middle cerebral arteries enter lateral fissure on each side
  • anterior cerebral arteries enter great longitudinal fissure
  • anterior communicating artery, joins together two anterior cerebral arteries to complete circle
• Anterior and posterior spinal arteries supply the medulla and spinal cord
• Posterior inferior cerebellar arteries supply inferior aspect of cerebellum
• Basilar artery

  • pontine arteries
  • anterior inferior cerebellar arteries supply anterior and inferior portions of cerebellum
• The internal carotid arteries and their branches are often referred to as the anterior circulation of the brain
• The vertebrobasilar arterial system and its branches are often referred to as the posterior circulation of the brain
• The meningeal vessels mainly supply the outer layer of the dura mater
• Arteries with meningeal branches:

  • maxillary artery
  • pharyngeal artery
  • occipital artery
  • vertebral artery
  • ethmoidal artery
• Extradural haematoma in middle meningeal artery rupture has a characteristic biconvex shape on CT
• The craniometric landmark, pterion, marks the junction of the frontal, parietal, sphenoid and temporal bones. The bone here is thin and vulnerable to fracture. Fracture of pterion can be especially dangerous due to potential laceration of a branch of the middle meningeal artery
• The venous drainage of the brain is by three sources with no valves

  • deep veins
  • superficial cerebral veins
  • dural venous sinuses
• The veins that drain the brain pierce the arachnoid and meningeal layers of the dura to empty into the dural venous sinuses, which finally drain into the internal jugular vein.
• Superficial veins, lie within subarachnoid space

  • superficial cerebral veins
  • superficial middle cerebral vein
  • superior anastomotic cerebral veins
  • inferior anastomotic cerebral veins
• Cerebellum is drained by superior and inferior cerebellar veins into transverse and sigmoid sinuses
• Dural venous sinuses are venous channels formed between the two layers of the dura mater - periosteal and meningeal
• Major dural venous sinuses are located in the attached borders of the falx cerebri and tentorum cerebelli, and on the floor of the cranial cavity

  • superior sagittal sinus
  • inferior sagittal sinus
  • straight sinus
  • confluence of sinuses
  • transverse sinus
  • sigmoid sinus
• The dural venous sinuses drain into internal jugular veins via sigmoid sinuses
• The cavernous sinus lies lateral to the body of the sphenoid bone. Connected by the anterior and posterior intercavernous sinuses to form a venous circle around the hypophysis (pituitary gland)
• Cavernous sinus contents

  • oculomotor nerve
  • trochlear nerve
  • ophthalmic nerve
  • maxillary nerve
  • abducens nerve
  • internal carotid artery
• Deep veins drain internal structures of forebrain

  • thalamostriate and choroidal veins unite to form the internal cerebral veins, which also unite to form great cerebral vein of Galen, that merges with the inferior sagittal sinus to form the straight sinus.
  • drain into dural venous sinuses
• Arteries supplying spinal cord

  • vertebral
  • ascending cervical
  • deep cervical
  • intercostal
  • lumbar
  • lateral sacral
• Three longitudinal arteries running from medulla of the brainstem to conus medullaris supply the spinal cord:

  • single anterior spinal artery from two vertebral arteries and reinforced by segmental arteries
  • paired posterior spinal arteries from either the vertebral or the posterior inferior cerebellar arteries
• Sulcal arteries from anterior spinal artery supply anterior two-thirds of cross-sectional area of spinal cord
• Anterior and posterior spinal arteries supply only the short superior part of spinal cord
• Lower part of spinal cord supplied by segmental medullary and radicular arteries that run along the nerve roots
• The anterior and posterior segmental medullary arteries are derived from spinal branches of the ascending cervical, deep cervical, vertebral, posterior intercostal and lumbar arteries
• The segmental medullary arteries occur mainly at the cervical and lumbosacral enlargements of the spinal cord
• The artery of Adamkiewicz is much larger than the other segmental medullary arteries, and usually arises via a spinal branch from an inferior intercostal or upper lumbar artery.
• The spinal veins generally follow the spinal arteries. There are usually three anterior and three posterior spinal veins, arranged longitudinally and freely communicate with each other. Drained by up to 12 anterior and posterior segmental medullary and radicular veins
• The spinal veins join the internal vertebral (epidural) venous plexuses in the epidural space.