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  1. 1. Arterial Anatomy of brain and Imaging of Strokes MODERATOR: DR.MANASA M.D PRESENTOR: N.LAKSHMI CHAITANYA
  2. 2. ARTERIAL ANATOMY  The anterior circulation consists of the intradural internal carotid artery (ICA) and its branches plus its two terminations, the anterior cerebral artery (ACA) and middle cerebral artery (MCA). Both the anterior communicating arteries (ACoAs) and the posterior communicating arteries (PCoAs) are also considered part of the anterior circulation.
  3. 3.  The is composed of the vertebrobasilar trunk and its branches, including its terminal bifurcation into the two posterior cerebral arteries (PCAs).
  4. 4. Intracranial Internal Carotid Artery  C1 (cervical) segment  C2 (Petrous) ICA Segment.  C3 (Lacerum) ICA Segment  C4 (Cavernous) ICA Segment  C5 (Clinoid) ICA Segment  C6 (Ophthalmic) ICA Segment.  C7 (Communicating) ICA Segment.
  5. 5. Variants and Anomalies Aberrant ICA (AbICA), Persistent stapedial artery, and Embryonic carotid-basilar anastomosis.
  6. 6. Aberrant ICA  Congenital vascular anomaly that enters the posterior middle ear cavity from below and hugs the cochlear promontory as it crosses the middle ear cavity.  present with pulsatile tinnitus.  otoscopic examination - a vascular appearing retrotympanic mass lying in the anteroinferior mesotympanum.
  7. 7.  An AbICA mimics the clinical appearance of paraganglioma (glomus tympanicum, glomus jugulare)  Never –biopsy.  The appearance of an AbICA on CT is pathognomonic. Axial bone CT shows a tubular lesion that crosses the middle ear cavity from posterior to anterior
  8. 8.  Coronal images show a round, well-delineated soft tissue density lying on the cochlear promontory.  Angiography (DSA, CTA, MRA) shows that the AbICA has a more posterolateral course than normal. A distinct angulation that resembles a 7 is often present, together with a change in contour and caliber (pinched appearance) before the segment resumes its normal course.
  9. 9. Persistent Stapedial Artery.  Rare congenital vascular anomaly in which the embryonic stapedial artery persists postnatally.  A PSA arises from the C2 (petrous) ICA at the genu between the vertical and horizontal segments.  The PSA passes through the stapes footplate and doubles the size of the anterior (tympanic) facial nerve segment. Intracranially, the PSA becomes the middle meningeal artery (MMA).
  10. 10.  Pathognomonic imaging findings are  (1) the absence of the foramen spinosum (because the MMA arises from the PSA, not the ECA) and  (2) an enlarged tympanic segment of the facial nerve.
  11. 11. Embryonic Carotid-Basilar Anastomoses.  Four types of PCBA.  From superior to inferior, these are  1)persistent trigeminal artery (CN V),  2)persistent otic artery (CN VIII),  3)persistent hypoglossal artery (CN XII), and  4)proatlantal intersegmental artery (C1-3)
  13. 13. ACA
  14. 14. MCA
  15. 15. PCA
  16. 16. Acute Cerebral Ischemia-Infarction
  17. 17.  The distinction between cerebral ischemia and cerebral infarction is subtle but important.  In cerebral ischemia, the affected tissue remains viable although blood flow is inadequate to sustain normal cellular function.  In cerebral infarction, frank cell death occurs with loss of neurons, glia, or both.  Hyperacute stroke designates events within the first 6 hours following symptom onset.
  18. 18.  In hyperacute stroke, cell death has not yet occurred, so the combined term acute cerebral ischemia-infarction is often used.  Acute strokes are those 6-48 hours from onset.
  19. 19. Pathophysiology of stroke
  20. 20.  Neurons in the CA1 area of the hippocampus, neocortex layers III, V, and VI, and the neostriatum are more vulnerable than other regions  The MCA is the most common site of large artery thromboembolic occlusion , followed by the PCA and vertebrobasilar circulation.
  21. 21.  ischemic core -The center of the affected brain parenchyma-typically has a CBF < 6-8 cm³/100 g/min.  Neuronal death with irreversible loss of function occurs in the core of an acute stroke.  ischemic penumbra- area surrounding the central core. CBF in the penumbra is significantly reduced, falling from a normal of 60 cm³/100 g/min to 10-20 cm³/100 g/min.(salvageable tissue)
  22. 22. THE FOUR "MUST KNOW" ACUTE STROKE QUESTIONS • Is there intracranial hemorrhage (or a stroke "mimic")? • Is a large vessel occluded? • Is part of the brain irreversibly injured? • Is an ischemic "penumbra" present?
  23. 23. CT Findings  A complete multimodal acute stroke CT protocol includes nonenhanced head CT, an arch-to-vertex CTA, and dynamic first-pass perfusion CT (pCT)  Recent studies have demonstrated that CTA with or without CTP improves diagnostic accuracy compared with NECT alone and does not delay IV tPA or endovascular therapy.
  24. 24. NECT  Initial NECT scans—even those obtained in the first 6 hours—are abnormal in 50-60% of acute ischemic strokes if viewed with narrow window width.  The most specific but least sensitive sign is a hyperattenuating vessel filled with acute thrombus
  25. 25. CT Early signs of ischemia ACUTE PHASE(2-6 HOURS)  Obscuration of lentiform nucleus  Dense MCA sign  Insular ribbon sign SUB-ACUTE PHASE(6-12 HOURS)  Sulcal effacement and low attenuation in region of infarct that extends to the periphery involving grey and white matter cytotoxic edema
  26. 26. Alberta stroke programme early CT score (ASPECTS)  The Alberta stroke programme early CT score (ASPECTS) is a 10- point quantitative topographic CT scan score used for patients with middle cerebral artery stroke(MCA). It has also been adjusted for the posterior circulation  An ASPECTS score less than or equal to 7 predicts a worse functional outcome at 3 months as well as symptomatic hemorrhage.
  27. 27. Posterior circulation  Variations of the ASPECT scoring system have been described for use in the posterior circulation and referred to as pc-ASPECTS.  thalami (1 point each)  occipital lobes (1 point each)  midbrain (2 points)  pons (2 points)  cerebellar hemispheres (1 point each)
  28. 28. CT ANGIO  CTA (with or without CT perfusion) quickly answers the second "must know" stroke question i.e., is a major vessel occlusion with a "retrievable" intravascular thrombus present?  CTA localizes and defines the extent of the intravascular thrombus, assesses collateral blood flow, and also characterizes atherosclerotic disease.
  29. 29. PERFUSION CT  pCT has three major parameters: cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT).  CBV is defined as the volume of flowing blood in a given volume of brain.  CBF is the volume of flowing blood moving through a given volume of brain in a specified amount of time.  MTT is the average time it takes blood to transit through a given volume of brain.
  30. 30.  The standard color scale is graduated from shades of red and yellow to blue and violet.  With CBV and CBF, perfusion is portrayed in red/yellow/green (highest) to blue/purple/black  In normal brain, there is bilaterally symmetric perfusion in the cerebral hemispheres with higher CBF and CBV in gray matter (cortex, basal ganglia) compared with white matter.
  31. 31.  Well-perfused gray matter appears red/yellow, white matter appears blue, and ischemic brain is blue/purple.  Totally nonperfused areas (i.e., the ventricles and densely ischemic central core of a major infarct) are black.
  32. 32.  Of the three standard parameters, MTT shows the most prominent regional abnormalities.  Here the color scales are reversed to emphasize the abnormally prolonged transit time in the ischemic brain.  With MTT, the slower the transit time, the closer to the red end of the scale. Brain with normal transit time appears blue.
  33. 33.  An important ancillary finding in patients with large MCA infarcts is reduced perfusion in the opposite cerebellar hemisphere  large MCA infarcts cause hypoperfusion with reduced CBF in the contralateral cerebellum, a phenomenon called crossed cerebellar diaschisis
  34. 34. MRI  T1W1: T1WI is usually normal within the first 3-6 hours  Subtle gyral swelling and hypointensity begin to develop within 12- 24 hours and are seen as blurring of the GM- WM interfaces.  T2/FLAIR: hyperintensity on FLAIR scans within the first 4 hours.  Nearly all strokes are FLAIR positive by 7 hours following symptom onset. T2 scans become positive slightly later, generally within 12-24 hours.
  35. 35.  Intraarterial hyperintensity on FLAIR is an early sign of stroke and indicates slow flow (not thrombosis).  FLAIR-DWI "mismatch" (negative FLAIR, positive DWI) has been suggested as a quick indicator of viable ischemic penumbra and eligibility for thrombolysis.  T2* GRE:Intraarterial thrombus can sometimes be as "blooming" hypointensity on T2* (GRE, SWI) studies
  36. 36.  T1 C+:Parenchymal enhancement is uncommon in acute/hyperacute ischemia  DWI and DTI: Cellular swelling begins to develop within minutes following an ischemic insult. ADC values decrease, producing high signal intensity on DWI images.  Around 95% of hyperacute infarcts show diffusion restriction on DWI, with hyperintensity on DWI and corresponding hypointensity on ADC.  DTI is even more sensitive than DWI, especially for pontine and medullary lesions.
  37. 37.  PMR: Restriction on DWI generally reflects the densely ischemic core of the infarct, whereas pMR depicts the surrounding "at-risk" penumbra.  A DWI-PWI mismatch is one of the criteria used in determining suitability for intraarterial thrombolysis.
  38. 38. Subacute Cerebral Infarcts  Early subacute strokes have significant mass effect and often exhibit HT, whereas edema and mass effect have mostly subsided by the late subacute period.  CT Findings. On NECT, the wedge-shaped area of decreased attenuation seen on initial scans becomes more sharply defined. Mass effect initially increases, then begins to decrease by 7-10 days following stroke onset. HT develops in 15-20% of cases and is seen as gyriform cortical or basal ganglia hyperdensity.
  39. 39.  CECT follows a "2-2-2" rule. Patchy or gyriform enhancement appears as early as 2 days after stroke onset, peaks at 2 weeks, and generally disappears by 2 months.  T1WI: Non hemorrhagic subacute infarcts are hypointense on T1WI and demonstrate moderate mass effect with sulcal effacement. Strokes with HT are initially isointense with cortex and then become hyperintense
  40. 40.  T2WI: Subacute infarcts are initially hyperintense compared with nonischemic brain. Signal intensity decreases with time, reaching isointensity at 1-2 weeks (the T2 "fogging effect").  FLAIR: Subacute infarcts are hyperintense on FLAIR. By 1 week after ictus, "final" infarct volume corresponds to the FLAIR- defined abnormality.  • T2*:○ "Blooming" HT ; ○ Prominent medullary veins  DWI ○ Pseudonormalization ○ T2 "shine-through"
  41. 41. Chronic Cerebral Infarcts  NECT scans show a sharply delineated wedge-shaped hypodense area that involves both gray matter (GM) and white matter (WM).  The adjacent sulci and ipsilateral ventricle enlarge secondary to volume loss in the affected hemisphere.  Chronic infarcts older than 2-3 months typically do not enhance on CECT.  MR scans show cystic encephalomalacia with CSF-equivalent signal intensity on all sequences.  Marginal gliosis or spongiosis around the old cavitated stroke is hyperintense on FLAIR.
  42. 42. Watershed ("Border Zone") Infarcts  Two distinct types of vascular border zones are recognized: an external (cortical) WS zone and an internal (deep) WS zone.
  43. 43. Artery of Percheron Infarction
  44. 44. THANK YOU

Editor's Notes

  • C2...vidian and caroticotympanic art
    C4 ...meningohypophyseal & inferlateral trunk
    C6...opthalmic & sup hypophyseal art
    C7...pcoa & AchA
  • Stenosis often present at communicating site.
  • Soft tissue m,ass on cochlear promontory
    Left ica passing more lat with a characteristic sharp angle resembling 7
  • connections form between the primitive carotid artery and the two longitudinal neural arteries
    With the exception of the PCoA, all these primitive arterial connections regress and then disappear
    If they fail to regress, a postnatal persistent ("primitive" or "embryonic") carotid-basilar anastomosis 
  • Anastomosis btw ant & post circu
    10 comp
  • A1..medial lenticulostriate arteries & recurrent art of heubne4r
    A2...orbito frontal& frontopolar art
    A3 terminates into pericallosal & callosomarginal 
  • A3 seg curve aroun cc genu
    A2 A1-ACoA junction to the corpus callosum rostrum
  • M1 lat frm ica to bifur
    M1 lenticulostriate art & ant tempo art
  • Most of the lateral surfac e of cerebral hemi
  • P1 precommuni P2 ambiebt P3 quadrig P4 calcarine 
    P1--posterior thalamoperforating arteries
    P2—posterior choroidal art
  • occipital lobe and posterior third of the medial & posterolateral surface of hemisphere
    inferior surface of the temporal lobe
  • A negative DWI does not exclude the diagnosis of stroke
  • Watershed zones are defined as the "border" or junction where two or more major arterial territories meet.