posterior circulation - applied anatomy

In the Name of God, Most Gracious, Most Merciful

- Dr.Mohammed Sadiq Azam

Final yr. Postgraduate MD (Int Med)

Deccan College of Medical Sciences

POSTERIOR CEREBRAL CIRCULATION &

BLOOD SUPPLY OF THE SPINAL CORD

• 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

OUTLINE

• 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

POSTERIOR CIRCULATION

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

• 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)

PCA

• 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.

PCA - ORIGINS

• 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

PERCHERON???

Ref: Matheus MG, Castillo M. Imaging of acute bilateral paramedian thalamic and mesencephalic infarcts. AJNR Am J Neuroradiol. 24 (10): 2005-8

• Supplies posterior cranial fossa structures:

• Medial area of occipital lobe

• Inferior temporal lobe

• Midbrain

• Thalamus

• Lesion causes:

• Visual agnosia

• Hemianopsia

• Alexia

• Loss of smell

POSTERIOR CEREBRAL ARTERY (PCA)

• Causes:• Atheroma/Emboli @ Basilar• Dissection @ Vertebral• Fibromuscular dysplasia

• Two syndromes• P 1 Syndrome• P 2 Syndrome

PCA Syndromes:

• 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

P 1 syndrome:

• 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.

P 1 syndrome… contd:

• 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

P 2 syndrome

• 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.

P 2 syndrome… contd:

• Commences as the union of

both vertebral arteries

• Terminates by dividing into

two Posterior cerebral

arteries.

• Branches:

• AICA

• Pontine arteries

• Superior cerebellar artery

• PCA

BASILAR ARTERY

• 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

Basilar artery – Branches

Structures supplied by BASILAR

• 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.

Basilar syndromes

• 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

Basilar 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

Superior 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.

Anterior inferior cerebellar artery occlusion

• 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

Occlusion of circumferentials/paramedians

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.

VERTEBRAL ARTERY

• Branches:• Anterior spinal artery• Posterior spinal artery• Posterior inferior cerebellar artery

VERTEBRAL… contd

• Largest branch of vertebral artery

• One of the three major supplies of the cerebellum

• Also supplies the lateral medulla

• Wallenberg syndrome (=LMS)

PICA

• Posterior meningeal branch

• Arises from opposite the formen magnum

• Supplies Falx cerebri

MENINGEAL BRANCHES OF VERTEBRAL a.

• 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.

ATHEROTHROMBOTIC LESIONS – V1 & V4

• Atheromatous disease is rare.

• Fibromuscular dysplasia, dissection common here

• Rarely due to encroachment from osteophytic spurs within vertebral foramina

LESIONS OF V2 & V3

• 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.

“SUBCLAVIAN STEAL”

LATERAL MEDULLARY 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.

WALLENBERG SYNDROME (=LMS)

• 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.

MEDIAL MEDULLARY SYNDROME

MEDIAL MEDULLARY SYNDROME

• 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)

CEREBELLAR INFARCTION

CIRCLE OF WILLIS – a note

CIRCLE OF WILLIS – a note

SPINAL ARTERIES:

ARTERY OF ADAMKIEWICZ

• Anterior spinal artery syndrome

• Posterior spinal artery syndrome

APPLIED ANATOMY – A WORD

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