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imaging and anatomy of blood supply of brain

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imaging and anatomy of blood supply of brain

  2. 2. • The brain is a highly vascular organ, its profuse blood supply characterized by a densely branching arterial network. It has a high metabolic rate that reflects the energy requirements of constant neural activity. • Loss of consciousness occurs in less than 15 seconds after blood flow to the brain has stopped, and irreparable damage to the brain tissue occurs within 5 minutes. • Cerebrovascular disease or stroke, occurs as a result of vascular compromise or haemorrhage and is one of the most frequent sources of neurologic disability.
  3. 3. • The brain is supplied by two internal carotid arteries and two vertebral arteries that form a complex anastomosis (circulus arteriosus, circle of Willis) on the base of the brain. • In general, the internal carotid arteries and the vessels arising from them supply the forebrain, with the exception of the occipital lobe of the cerebral hemisphere, and the vertebral arteries and their branches supply the occipital lobe, the brain stem and the cerebellum. ARTERIAL SUPPLY TO BRAIN
  4. 4. INTERNAL CAROTID ARTERY • The internal carotid artery arises from the bifurcation of the common carotid artery, most frequently between C3 and C5 vertebral level, ascends in the neck and enters the carotid canal of the temporal bone. • Origin -Lateral to ECA. • Can be divided into number of segments between the bulb and its bifurcation into MCA and ACA
  5. 5. ECA Internal carotid- carotid bulb Left CCA 3-D CTA
  6. 6. Bouthillier classification of ICA segments Bouthillier et al described a seven segment internal carotid artery (ICA) classification system: – cervical segment – petrous segment – lacerum segment – cavernous segment – clinoid segment – ophthalmic (supraclinoid) segment – communicating (terminal) segment
  7. 7. Cervical segment • Cervical ICA extends from carotid bifurcation to skull base. – No narrowing – No dilatation – No branches – No tapering Course – crosses behind and medial to ECA
  8. 8. Variants – cervical segment • 10%- ICA originates medial to ECA ICA ECA
  9. 9. • Anomalous ECA branches arises from cervical ICA – The ascending pharyngeal artery occasionally takes off from the proximal ICA also, as does the occipital. • Persistent embryonic vesels may anastomose with vertebrobasilar system. – Persistent hypoglossal artery is one such branch. The persistent hypoglossal artery originates from the internal carotid artery at the levels of the C1 through C3 vertebral bodies, courses through the hypoglossal canal, and anastomoses with the basilar artery.
  10. 10. Persistent hypoglossal artery. Axial image from CT angiography shows an artery that courses through the hypoglossal canal (arrows). CT angiogram depicts a hypoglossal artery (arrowhead) that arises from the proximal internal carotid artery (arrow) at the C2 vertebral level and anastomoses with the basilar artery.
  11. 11. • This is the ICA segment inside the petrous bone and partially within foramen lacerum. • The artery enters the skull at right angle and has an initially ascending course (vertical petrous subsegment), turning anteromedially (horizontal petrous subsegment) and exits the petrous bone at foramen lacerum. Petrous segment
  12. 12. Vertical •2 subsegments joined at genu •Short vertical segment – anterior to IJV •Genu – petrous ICA turns anteromedially in front of cochlea •Longer horizontal segment Horizontal Genu
  13. 13. DSA
  14. 14. MRA
  15. 15. 3D-DSA of petrous segment aneurysm
  16. 16. Variant • Aberrant Carotid Artery – This vessel is, in fact, not the “ICA”, but rather ascending pharyngeal reconstitution of the true ICA in the petrous segment, due to cervical ICA agenesis. – The aberrant carotid is made up of the ascending pharyngeal artery, its inferior tympanic branch, and the caroticotympanic branch of the ICA.
  17. 17. The vessel has a characteristic lateral swing within the petrous bone (red arrows), bringing it into the middle ear cavity, which can be appreciated on MR, CT, and angio.
  18. 18. Note the posterior course of the intratympanic segment ofthe aberrant carotid artery compared with the normal.
  19. 19. •Reduced caliber •Lateral sling
  20. 20. Variant -Aberrant ICA Aberrant course •Posterolateral course thro temporal bone •Reduced diameter of ICA •Visible pulsatile mass in hypotympanum •Bony plate separating ICA from tympanic cavity absent •Vertical segment of carotid canal absent Normal course of ICA •Anteromedial course thro temporal bone •ICA anterior to IJV •In front of cochlea • 2 segments
  21. 21. Lacerum Segment Small segment that extends from petrous apex, above foramen lacerum curving upwards towards and lies extradurally until it reaches petrolingual ligament after this it becomes the cavernous segment Covered by trigeminal ganglion No branches
  22. 22. • Defined as that portion of the ICA located within the cavernous sinus. Cavernous ICA
  23. 23. C4 segments 1. Ascending (posterior vertical ) 2. Posterior genu 3. Horizontal 4. Anterior genu 5. Anterior vertical 1 Starts from petrous apex Terminates at its entrance into intracranial subarchnoid space adjacent to anterior clinoid process. Covered by trigeminal ganglion posteriorly. Has 5 segments
  24. 24. • The cavernous segment ends when the ICA passes through an opening in the anterior cavernous sinus wall called the “proximal dural ring” (PDR). • A short but very important segment, where the ICA is sandwiched between the PDR and the Distal Dural Ring, (which marks the intradural transition), is neither intracavernous nor intradural. Clinoid segment C5
  25. 25. The anterior clinoid and sphenoid sinus position, is outlined in white. The proximal ring (yellow line) extends from clinoid undersurface to medial ICA wall. The distal ring (purple line) comes off the clinoid roof. The Clinoid segment is defined as the space between the two rings.
  26. 26. Opthalmic segment C6 Extends from distal dural ring at superior clinoid to just below posterior communicating artery (PCoA) origin Branches – •Opthalmic artery ANT CLINOID PROCESS C6 POST COMM ARTERY
  27. 27. Mid arterial phase DSA Lateral view MRA Lateral DSA
  28. 28. Variations in Origin Of Opthalmic Artery In its “classic” location, the ophthalmic ostium is located just distal (1mm) to the dural ring and therefore intradural. However, the vessel may arise either somewhat more distal to the ring (as far up as the ACOM — ventral ophthalmic variant), or somewhat proximal — in which case it may be extradural – within “transitional” or cavernous segments
  29. 29. lateral DSA of RT ICA injection, demonstrating ophthalmic artery origin from anterior genu of the ICA, proximal to its usual location
  30. 30. •Extends from below PCoA to terminal ICA bifurcation. •Passes between optic and occulumotor nerve. C7 segment branches Posterior communicating artery Anterior choroidal artery Lateral DSA AChA PCoA Communicating C7 Segment
  31. 31. Posterior communicating artery •Arises – posterior aspect of intradural ICA just below anterior choroidal artery •Course – posterolaterally above the occulumotor nerve to join posterior cerebral artery •Branches – anterior thalamoperforating arteries •Supplies – optic chiasma, pituitary stalk , thalamus , hypothalamus.
  32. 32. Lateral late arterial DSA MRA
  33. 33. Computed tomography angiography of the brain illustrating saccular aneurysm (blue arrow) in the region of the right posterior communicating artery.
  34. 34. Posterior Communicating Artery Anomalies • Fetal Origin of the Posterior Cerebral Artery – A fetal PCOM or fetal origin of the posterior cerebral artery is a very common variant in the posterior cerebral circulation. – The posterior communicating artery (PCOM) is larger than the P1 segment of the posterior cerebral artery (PCA) and supplies the bulk of the blood to the PCA. – The P1 can be small (hypoplastic) or absent. The significance is in the stroke pattern, as the PCA will be a part of the anterior circulation.
  35. 35. CT angiogram shows bilateral fetal posterior cerebral arteries (arrows). Both P1 segments are absent.
  36. 36. • DWI in a Young patient with an internal carotid artery occlusion resulting in acute MCA and PCA territory infarcts due to a fetal origin of posterior cerebral artery.
  37. 37. Posterior Communicating Artery Infundibulum • An infundibulum is a funnel shaped region of dilatation at the origin of the posterior communicating artery from the internal carotid artery. • It may be round or conical, has a diameter of less than 2 mm, and is symmetric. The internal carotid artery is at its base, and the posterior communicating artery arises from its apex. • An infundibulum must be distinguished from aneurysms of the posterior communicating artery and internal carotid artery
  38. 38. CT angiogram shows a posterior communicating artery (arrowhead) that arises from the apex of a funnel-shaped infundibulum (arrow). The base of the infundibulum is located at the origin of the posterior communicating artery
  39. 39. Terminal Branches of ICA • Anterior Choroidal artery • Middle cerebral artery • Anterior cerebral artery
  40. 40. Segments The ACA is divided into three segments: A1 (horizontal): origin from the ICA to the anterior communicating artery (ACOM). ~14 mm in length A2 (vertical): from ACOM to the origin of the callosomarginal artery A3 (callosal): distal to the origin of the callosomarginal artery Anterior cerebral artery The anterior cerebral artery along with the middle cerebral artery, forms at the termination of the internal carotid artery. It is the smaller of the two, and arches anteromedially to pass anterior to genu of the corpus callosum, dividing as it does so into its two major branches; pericallosal and callosomarginal arteries
  41. 41. A1 (horizontal): origin from the ICA to the anterior communicating artery (ACOM)
  42. 42. A2 (vertical): from ACOM to the origin of the callosomarginal artery
  43. 43. Arise from A1 segment- perforating branches. • Pass cephalad thro anterior perforated substance. • Supply head of caudate nucleus and anterior limb of IC, putamen . Medial lenticulostriate artery.
  44. 44. Recurrent Artery of Heubner • Largest of the perforating branches. • May arise from A1 or A2 segment. • A1 – 44% • Proximal A2 – 50% • ACoA – less common • Derives its name from the fact that it doubles back on its parent artery at an acute angle to join lenticulostriate vessel. • Lies parallel to A1 . • Supplies inferior part of anterior limb of internal capsule
  45. 45. A2 segment- Interhemispheric segment From ACoA junction Ascend in front of 3rd ventricle in cistern of lamina terminalis Curves around corpus callosum genu gives terminal branches A2 terminal branches- Pericollasal Collasomarginal
  46. 46. Cortical A3 segment • Supply the anterior 2/3rds of medial hemispheric surface and small superior area over the convexities. • Callosomarginal a.– lies in cingulate gyrus supplies medial frontal lobe • Pericallosal a.– course along the posterior aspect of corpus callosum and supplies it and medial parietal lobe
  47. 47. Callosomarginal Pericallosal A2 Segment
  48. 48. CT study of brain shows infarct involving right para sagittal frontal lobe. Area of involvement corresponds to right ACA territory.
  49. 49. CT study of brain shows infarct involving left para sagittal frontal lobe. Area of involvement corresponds to left ACA territory.
  50. 50. ACA– ACoA complex • ACoA -Part of COW -not a true branch of ACA • Branches – perforating • Supply –Lamina terminalis , Hypothalamus , Anterior commissure , Fornix, Septum pellucidum , Para olfactory gyrus , Subcellosal region , Anterior part of cingulate gyrus
  51. 51. Variants ACA – ACoA Complex • Azygos anterior cerebral artery – It represents persistence of the embryonic median artery of the corpus callosum . – Bilaterally, the anterior cerebral artery territories are supplied by a single midline A2 trunk. – The anomaly is clinically relevant also because in the event of anterior cerebral artery occlusion secondary to thromboembolic disease or surgical error, the resultant ischemia affects both hemispheres
  52. 52. Azygos anterior cerebral artery. Multidetector CT angiogram shows convergence of the A1 segments to form a single midline A2 trunk.
  53. 53. • Anterior Cerebral Artery Trifurcation • It is defined as the occurrence of three A2 segments. Multidetector CT angiogram shows three A2 segments (arrows) that arise from the anterior communicating artery.
  54. 54. Bihemispheric Anterior Cerebral Artery • This anomaly is characterized by hypoplasia of one A2 segment, with the contralateral A2 segment providing the major arterial supply bilaterally to the anterior cerebral artery territory Multidetector CT angiogram depicts a dominant or bihemispheric A2 segment (arrow) that supplies bilateral anterior cerebral artery territories and a contralateral nondominant A2 segment (arrowhead).
  55. 55. A1 Segment Absence or Hypoplasia • In the presence of either variant, the contralateral anterior cerebral artery may supply part or all of the territory of the normal anterior cerebral artery via a large anterior communicating artery Absence of an A1 segment of the anterior cerebral artery. Multidetector CT angiogram shows the origin of both A2 segments from a single, unilateral A1 segment.
  56. 56. Absent Anterior Communicating Artery Absence of the anterior communicating artery. Multidetector CT angiogram demonstrates absence of the anterior communicating artery and equal caliber of the A1 segments
  57. 57. Middle cerebral artery • The MCA arises from the internal carotid artery (ICA) as the larger of the two main terminal branches (MCA and anterior cerebral artery) and continues into the lateral sulcus where it branches and provides many branches that supply the cerebral cortex.
  58. 58. Segments • The MCA is divided into four segments: – M1: from the origin to bifurcation/trifurcation (the limen insulae); also known as horizontal or sphenoidal segment – M2: also known as insular segment, from bi(tri)furcation to circular sulcus of insula where it makes hairpin bend to continue as M3 – M3: opercular branches (those within the Sylvian fissure); also known as opercular segment – M4: branches emerging from the Sylvian fissure onto the convex surface of the hemisphere; also known as cortical segment
  59. 59. Lateral lenticulostriate arteries • The lateral lenticulostriate arteries arise from the proximal middle cerebral artery (MCA) and supply the lateral portion of the putamen and external capsule as well as the upper internal capsule.
  60. 60. Sylvian segment [M3] territory • Supplies • Inferolateral frontal lobe • Insular cortex • Parietal lobe • Temporal lobe Cortical segment territory [M4] • Supplies – • Lateral cerebrum • Insula • Ant- lateral temporal lobe
  61. 61. MCA Territory infarct
  62. 62. Variant • Accessory Middle Cerebral Artery – An accessory middle cerebral artery is an artery that arises from the anterior cerebral artery and courses parallel to the M1 segment of the middle cerebral artery, supplying the anterior- inferiorregion of the frontal lobe – It may be difficult to differentiate an accessory middle cerebral artery from a duplicated middle cerebral artery. – A smaller middle cerebral artery branch arising from the anterior cerebral artery is designated as an accessory middle cerebral artery, whereas a smaller middle cerebral artery branch arising from the distal carotid artery is called a duplicated middle cerebral Artery – Comparison with the level of carotid bifurcation and the pattern of branching on the opposite side may be helpful for identifying this variant
  63. 63. Accessory middle cerebral artery. Multidetector CT angiogram shows the main middle cerebral artery (arrowhead) with a smaller-caliber accessory middle cerebral artery (arrow) that arises from the A1 segment. Duplication of the middle cerebral artery. Multidetector CT angiogram depicts the main middle cerebral artery branch, which arises directly from the distal internal carotid artery (arrow), and a smaller- caliber duplicate middle cerebral artery that arises from a more proximal site (arrowhead).
  65. 65. Vetebral artery • The vertebral artery (VA) arises from the subclavian artery, ascends in the neck to supply the posterior fossa and occipital lobes as well as provides segmental vertebral and spinal column blood supply.
  66. 66. • Origin – The origin of the VA is usually from the posterior superior part of the subclavian arteries bilaterally, although the origin can be variable: • brachiocephalic artery (on the right) • aortic arch: 6% of cases – The VA is normally 3-5 mm in diameter and the ostium is the most common site of stenosis.
  67. 67. Segments • The vertebral artery is typically divided into 4 segments: – V1: origin to transverse foramen of C6 – V2: from the transverse foramen of C6 to the transverse foramen of C2 – V3: from C2 to the dura – V4: from the dura to their confluence to form the basilar artery
  68. 68. Extracranial VA branches 1. V1-Small segmental spinal/ meningeal/ muscular branches. 2. V2- Anterior Meningeal artery , muscular branches. 3. V3 -Posterior Meningeal artery – Courses along posterior arch of atlas. – Supplies falx cerebri – Variant – origin from ECA / PICA. – Greatly enlarged with vascular malformations and neoplasms Posterior meningeal artery
  69. 69. Intracranial branches • Anterior spinal artery – Joins ASA from opposite VA along anteromedial sulcus of cervical cord. – Medial medullary syndrome [Dejerine syndrome] • Posterior inferior cerebellar artery – Arises from distal VA – Lateral Medullary syndrome [Wallenberg syndrome]
  70. 70. • Abnormal hyperintensity is noted in the right medial medulla on both T2- and diffusion-weighted scans, which corresponds to vasogenic and cytotoxic edema, respectively • Medial medullary syndrome
  71. 71. FLAIR image showing ischemic infarct in left medulla. Lateral Medullary Syndrome
  72. 72. Variants – • Persistent vertebrobasilar anastamosis • Left VA – aortic arch origin – 5% • Hypolastic VA – 40 % Hypoplastic VA
  73. 73. Posterior inferior cerebellar artery • Segments • anterior medullary segment – Front of medulla • lateral medullary segment – Along side of medulla caudally to level of CN 9-11 • posterior medullary segment – ascends posterior to the medulla behind CN IX and CN X. • supratonsillar segment
  74. 74. anterior medullary segment lateral medullary segment posterior medullary segment supratonsillar segment
  75. 75. • Supply • Has a variable territory depending on the size of the AICA. • Typically it may supply: – posteroinferior cer ebellar hemisphere s (up to the great horizontal fissure) – cerebellar tonsils: 85% of the time – inferior portion of the vermis – lower part of the medulla: 50%
  76. 76. Basilar Artery • It artery arises from the confluence of the left and right vertebral arteries at the base of the pons as they rise towards the base of the brain. • The basilar artery runs cranially in the central groove of the pons towards the midbrain within the pontine cistern. • Terminates in the interpeduncular cistern by dividing into posterior cerebral arteries.
  77. 77. MRA
  78. 78. Branches 1. AICA – Anterior Inferior Cerebellar Artery – 1st major branch. – Posterior laterally in cerebellopontine angle cistern. – Supplies- • Inferolateral pons • Middle cerebellar peduncle • Flocculus • Anterolateral cerebelllar hemisphere
  79. 79. SCA- Superior Cerebellar Artery – – Arises from BA apex. – Supplies – • Superior surface of vermis n cerebellar hemisphere. • Deep cerebellar white matter. • Dentate nucleus.
  80. 80. Posterior cerebral artery • The posterior cerebral arteries (PCA) are the terminal branches of the basilar artery and supply the occipital lobes and posteromedial temporal lobes. • Segments: The PCA is divided into four segments: – P1: from it origin at the termination of the basilar artery to posterior communicating artery (PCOM), within interpeduncular cistern. – P2: from the PCOM around the mid-brain(lies in ambien cistern) – P3: quadrigeminal segment (segment within the quadrigeminal cistern) – P4: cortical segment (e.g. calcarine artery, within the calcarine fissure)
  81. 81. CT ANGIO
  82. 82. P1 precommunicating / peduncular • Br – • Posterior thalamoperforating- Thalamus , Midbrain • Medial posterior choroidal artery – anteromedially along roof of 3rd ventricle – tectal plate , midbrain , thalamus posterior , pineal gland , tele choroidae of 3rd ventricle. P2 ambient / crural • Br – • Thalamogeniculate arteries- MGB , pulvinar , brachium superior colliculus , crus cerebri , LGB • Lateral post choroidal artery – over pulvinar of thalamus – posterior thalamus , lateral ventricular choroid plexus
  83. 83. P1 Segment supplying Thalamus and Midbrain P COM P2 SUPPLYING Crus Cerebri Lateral post choroidal artery lateral ventricular choroid plexus
  84. 84. P3 quadrigeminal Behind midbrain in quadrigeminal plate cistern Inferior temporal artery • Undersurface of temporal lobe • Anastamose -MCA Parietooccipital artery • Posterior 1/3rd interhemispheric surface • Anastamose with ACA Calcarine artery( P4 ) • Visual cortex • Occipital pole Posterior pericollasal artery (splenial) • Splenium of corpus callosum • ACA
  85. 85. MRI Axial FLAIR images of Brain shows infarct involving right thalamus, right medial occipital and medial temporal lobe. Area of involvement corresponds to right proximal PCA territory.
  86. 86. Circle of Willis • It is formed by an arterial polygon as the internal carotid and vertebral systems anastomose around the optic chiasm and infundibulum of the pituitary stalk. • Vessels comprising the circle of Willis: – left and right internal carotid arteries(ICA) – horizontal (A1) segments of the left and right anterior cerebral arteries (ACA) – anterior communicating artery (ACOM) – left and right posterior communicating arteries (PCOM) – horizontal (P1) segments of left and right posterior cerebral arteries (PCA) – basilar artery(tip)
  87. 87. 3DVRT CTA MRA CT MRA 1. A1 2. P1 3. PCoA 4. ACoA
  88. 88. Other Variants of the Cerebral Circulation • Duplications – A duplication is defined as two distinct arteries with separate origins and no distal arterial convergence Multidetector CT angiogram clearly demonstrates duplication of the anterior communicating artery (arrow), with each vessel originating separately from an anterior cerebral artery.
  89. 89. • Fenestration, by contrast, is defined as a division of the arterial lumen into distinctly separate channels, each with its own endothelial and muscularis layers, while the adventitia may be shared. • More common in the vertebrobasilar arteries than in the arteries of the anterior circulation. Multidetector CT angiogram shows dual channels with a common origin from the anterior cerebral artery (arrow).
  90. 90. • An association has been observed between fenestration and aneurysm formation. • It has been postulated that turbulent flow created by defects in the tunica media at the proximal and distal ends of a fenestrated segment leads to aneurysm formation. • These gaps in the media, combined with increased hemodynamic stress, are believed to contribute to the increased prevalence of aneurysms among patients with fenestration.