Applied Anatomy of the posterior cerebral circulation

2. POSTERIOR CEREBRAL
CIRCULATION &
BLOOD SUPPLY OF THE
SPINAL CORD
- Dr.Mohammed Sadiq Azam
Final yr. Postgraduate MD (Int Med)
Deccan College of Medical Sciences

3. OUTLINE
• What is posterior circulation?
• Posterior cerebral artery
• P1 & P2 syndromes
• Vertebral arteries
• Subclavian steal
• PICA
• Wallenberg syndrome
• Basilar artery
• “Locked-in” state
• Circle of Willis – A Note
• Spinal cord – Blood supply
• ASA syndrome

4. POSTERIOR CIRCULATION
• Comprises of:
• Paired vertebral arteries
• Basilar artery
• Paired posterior cerebral arteries
• Vertebrals join to form basilar at the pontomedullary
junction
• Basilar divides into two posterior cerebrals in the
interpeduncular fossa.
• These 3 give rise to long & short circumferential branches
and to smaller deep penetrating branches.
• Supply: Cerebellum, Medulla, Pons, midbrain, subthalamus,
thalamus, hippocampus and medial temporal & occipital
lobes

5. VERTEBROBASILAR SYSTEM - Branches
• Vertebral Artery
• Posterior spinal artery
• Posterior inferior cerebellar artery
• Anterior spinal artery
• Basilar artery
• Anterior inferior cerebellar artery
• Pontine arteries
• Superior cerebellar artery
• Posterior cerebral artery
• Thalamoperforate arteries
• Choroidal arteries
• Cortical branches

6. PCA
• Terminal branch of the basilar artery
• Paired
• At the interpeduncular fossa
• Branches:
• P 1 segment: Proximal PCA prior to junction of PCA with posterior
communicating (=Precommunal segment)
Penetrating branches of P1:Thalamogeneculate, Percheron,
posterior choroidal)
• P 2 segment: Distal PCA (distal to junction of PCA and posterior
communicating)

7. PCA - ORIGINS
• 75% cases: from bifurcation of basilar artery
• 20% cases: One PCA arises from ipsilateral ICA via
posterior communicating artery
• 5% cases: BOTH PCAs originate from respective
ipsilateral ICAs. The P1 segment (precommunal) of the
true PCA is atretic in such cases.

8. PERCHERON???
• The artery of Percheron is a rare variant of the posterior
cerebral circulation.
• The term is used to refer to a solitary arterial trunk that
branches from one of the proximal segments of either
posterior cerebral artery.
• It supplies blood to the paramedian thalami and the
rostral midbrain bilaterally.
• Percheron infarct: bilateral thalamic and
mesencephalic infarctions ; clinically, often obtunded,
comatose, or agitated, with associated hemiplegia or
hemisensory loss
Ref: Matheus MG, Castillo M. Imaging of acute bilateral
paramedian thalamic and mesencephalic infarcts. AJNR Am J
Neuroradiol. 24 (10): 2005-8

9. POSTERIOR CEREBRAL ARTERY (PCA)
• Supplies posterior cranial fossa structures:
• Medial area of occipital lobe
• Inferior temporal lobe
• Midbrain
• Thalamus
• Lesion causes:
• Visual agnosia
• Hemianopsia
• Alexia
• Loss of smell

10. PCA Syndromes:
• Causes:
• Atheroma/Emboli @ Basilar
• Dissection @ Vertebral
• Fibromuscular dysplasia
• Two syndromes
• P 1 Syndrome
• P 2 Syndrome

11. P 1 syndrome:
• Area infarcted:
• Ipsilateral subthalamus
• Medial thalamus
• Ipsilateral cerebral peduncle
• Midbrain
• Weber’s/Claude’s syndrome can occur
• Contralateral hemiballismus +/-
• A. of Percheron occlusion: Upward gaze paresis,
drowsiness, abulia

12. P 1 syndrome… contd:
• B/L Prox PCA occlusion: Extensive infarction:
• Coma, Unreactive pupils, b/l pyramidal signs, decerebrate rigidity
• Penetrating branches of thalamic and thalamogeniculate
arteries if occluded:
• Less extensive syndromes
• Thalamic Dejerine-Roussy syndrome:
• Contralateral hemisensory loss
• Followed by agonising, searing, burning pain
• Persistent, poor response to analgesics
• Anticonvulsants (Carbamazepine, gabapentin) & TCAs used.

13. P 2 syndrome
• Infarction of:
• Medial temporal and occipital lobes
• Contralateral homonymous hemianopia with macular sparing
• Occasional only the upper quadrant is involved.
• If visual association areas are spared, patient is aware of the
defects.
• Dominant medial temporal lobe and hippocampal lesions: Acute
disturbances in memory – usually recovers
• Alexia sans Agraphia
• Visual agnosia
• Amnestic aphasia
• Peduncular hallucinosis

14. P 2 syndrome… contd:
• Anton’s blindness
• Gun barrel vision
• Balint’s syndrome
• Palinopsia
• Asimultanagnosia
• Embolic occulsion of top of basilar:
• HALLMARK is sudden onset of bilateral signs, including
ptosis, pupillary asymmetry or lack of reaction to light,
somnolence.

15. BASILAR ARTERY
• Commences as the union of
both vertebral arteries
• Terminates by dividing into two
Posterior cerebral arteries.
• Branches:
• AICA
• Pontine arteries
• Superior cerebellar artery
• PCA

16. Basilar artery – Branches
• Three groups:
• Paramedian, 7-10 in number, supply a wedge of pons on
either side of midline
• Short circumferential, 5-7, supply lateral 2/3rd of Pons,
middle & superior cerebellar peduncles.
• Bilateral long circumferentials (curve around pons to supply
cerebellum):
• Superior cerebellar art
• Anterior inferior cerebellar art

17. Structures
supplied by
BASILAR

18. Basilar syndromes
• Complete basilar occlusion
• Constellation of bilateral long tract signs (sensory & motor)
with signs of cranial nerve & cerebellar dysfunction.
• “Locked-in” state:
• Preserved consciousness with quadriplegia & cranial nerve
signs
• GOAL: To identify impending Basilar occlusion before
infarction occurs.
• Series of TIAs, slowly progressive, fluctuating stroke herald
an occlusion of distal vertebral or proximal basilar artery.

19. Basilar occlusion
• Proximal occlusion: Vertigo (swimming, swaying,
moving, unsteadiness or light-headedness)
• Warning signs: Diplopia, dysarthria, facial or circumoral
numbness and hemisensory symptoms.
• Symptoms of basilar BRANCH TIA  unilateral
sensorimotor, cranial nerve symptoms
• Basilar ARTERY TIA  bilateral, “herald” hemiparesis,
short lived TIAs, multiple episodes/day.
• Gaze paresis/Internuclear ophthalmoplegia associated
with ipsilateral hemiparesis  B/L BS infarction

20. Superior cerebellar artery occlusion
• Severe ipsilateral cerebellar ataxia
• Nausea & vomitings
• Dysarthria
• Contralateral loss of pain & temperature over
extremities, body & face.
• Partial deafness, ataxic tremor of ipsilateral UL,
Horner’s syndrome & Palatal myoclonus rare

21. Anterior inferior cerebellar artery occlusion
• Territory of supply inverse to PICA
• Symptoms:
• Ipsilateral:
• Deafness, Facial weakness, Vertigo, Nausea, Vomitings,
Nystagmus, Tinnitus, Cerebellar ataxia, Horner’s, paresis of
conjugate lateral gaze
• Contralateral:
• Loss of pain & temperature
• Occlusion close to the origin of the artery may cause CST
signs.

22. Occlusion of circumferentials/paramedians
• Occlusion of one of the short circumferentials:
• Affects lateral 2/3rd of Pons and middle or superior cerebellar
peduncle
• Occulsion of one of the paramedians:
• Affects a wedge-shaped area on either side of the medial
pons

23. Vertebral
artery

24. VERTEBRAL ARTERY
• Commences as a branch of the subclavian on left and
brachiocephalic on right and terminates by joining its
brother to form the basilar artery
• Four parts:
• V-1: Preforaminal- origin to entrance into C5 or C6 foramen
• V-2: Foraminal- vertebral foramina C6 to C2
• V-3: C2 to dura- passes through transverse foramen and
circles around the arch of the atlas to pierce the atlas at the
formen magnum
• V-4: Intradural-courses upwards and joins other to form
basilar. Gives branches that supply BS & cerebellum.

25. VERTEBRAL… contd
• Branches:
• Anterior spinal artery
• Posterior spinal artery
• Posterior inferior cerebellar artery

26. PICA
• Largest branch of vertebral artery
• One of the three major supplies of the cerebellum
• Also supplies the lateral medulla
• Wallenberg syndrome (=LMS)

27. MENINGEAL BRANCHES OF VERTEBRAL a.
• Posterior meningeal branch
• Arises from opposite the formen magnum
• Supplies Falx cerebri

28. ATHEROTHROMBOTIC LESIONS – V1 & V4
• Predilection for V1 and V4
• Usually lesion of one vertebral does not cause TIAs.
• TIAs occur if one is atretic and other is developing
occlusion.
• Symptoms:
• Syncope
• Vertigo
• Alternating hemiplegia
• ‘Sets the stage for thrombosis’
• Stenosis proximal to origin of PICA can threaten lateral
medulla & posterior inferior surface of cerebellum.

29. LESIONS OF V2 & V3
• Atheromatous disease is rare.
• Fibromuscular dysplasia, dissection  common here
• Rarely due to encroachment from osteophytic spurs
within vertebral foramina

30. “SUBCLAVIAN STEAL”
• Subclavian occluded proximal to
origin of vertebral.
• Leads of reversal in the direction of
blood flow in the ipsilateral
vertebral artery.
• Exercise of ipsilateral arm may
increase demand on vertebral flow,
leading to posterior circulation
TIAs.

31. LATERAL MEDULLARY SYNDROME (=LMS)

32. WALLENBERG SYNDROME (=LMS)
• = Lateral medullary syndrome/PICA syndrome
• Embolic occlusion/thrombus of V4  ischemia of lateral
medulla
• Vertigo, numbness of ipsilateral face & contralateral limbs,
diplopia, hoarseness, dysarthria and ipsilateral Horner’s
syndrome.
• Most cases occur due to VERTEBRAL ARTERY OCCLUSION.
PICA occlusion is responsible in the remainder.
• Occlusion of medullary penetrating branches results in
partial syndromes.
• Hemiparesis is NOT a feature of vertebral artery occlusion,
however, quadriparesis can occur due to ASA occlusion.

33. MEDIAL MEDULLARY SYNDROME
• Infarction of the pyramid
• Contralateral hemiparesis of the
arm & leg
• Sparing the face
• If the medial lemniscus &
emerging hypoglossal nerve
fibres are involved,
contralateral loss of JPS &
ipsilateral tongue weakness
occur.

34. MEDIAL MEDULLARY SYNDROME

35. CEREBELLAR INFARCTION
• Can lead to sudden respiratory arrest
• Due to raised ICP in the posterior fossa
• Symptoms:
• Drowsiness
• Babinski signs
• Dysarthria
• Bifacial weakness maybe absent, or present only briefly, before
respiratory arrest ensues.
• Gait unsteadiness, headache, dizziness, nausea and vomiting
maybe the only early symptoms and signs and should arouse
suspicion.
• D/D: Viral labrynthitis (Headache, neck stiffness & unilateral
dysmetria favor stroke)

36. CIRCLE OF WILLIS – a note

37. CIRCLE OF WILLIS – a note

38. SPINAL ARTERIES:

39. ARTERY OF ADAMKIEWICZ

40. APPLIED ANATOMY – A WORD
• Anterior spinal artery syndrome
• Posterior spinal artery syndrome

41. THANK YOU