Posterior Circulation - Applied Anatomy

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Applied anatomy of the Postrior cerebral circulation

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In the Name of God, Most Gracious, Most Merciful: 

In the Name of God, Most Gracious, Most Merciful

POSTERIOR CEREBRAL CIRCULATION & BLOOD SUPPLY OF THE SPINAL CORD: 

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

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 OUTLINE

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 POSTERIOR CIRCULATION

VERTEBROBASILAR SYSTEM - Branches: 

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

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) PCA

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. PCA - ORIGINS

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

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 POSTERIOR CEREBRAL ARTERY (PCA)

PCA Syndromes:: 

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

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 P 1 syndrome:

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. P 1 syndrome… contd :

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 P 2 syndrome

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. P 2 syndrome… contd :

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 BASILAR ARTERY

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 2/3 rd 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: 

Structures supplied by BASILAR

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. Basilar syndromes

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 Basilar occlusion

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 Superior cerebellar artery occlusion

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. Anterior inferior cerebellar artery occlusion

Occlusion of circumferentials/paramedians: 

Occlusion of one of the short circumferentials : Affects lateral 2/3 rd 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: 

Vertebral artery

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

VERTEBRAL… contd: 

Branches: Anterior spinal artery Posterior spinal artery Posterior inferior cerebellar artery VERTEBRAL… contd

PICA: 

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

MENINGEAL BRANCHES OF VERTEBRAL a.: 

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

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. ATHEROTHROMBOTIC LESIONS – V1 & V4

LESIONS OF V2 & V3: 

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

“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. “SUBCLAVIAN STEAL”

LATERAL MEDULLARY SYNDROME (=LMS): 

LATERAL MEDULLARY SYNDROME (=LMS)

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. WALLENBERG SYNDROME (=LMS)

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. MEDIAL MEDULLARY SYNDROME

MEDIAL MEDULLARY SYNDROME: 

MEDIAL MEDULLARY SYNDROME

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) CEREBELLAR INFARCTION

CIRCLE OF WILLIS – a note: 

CIRCLE OF WILLIS – a note

CIRCLE OF WILLIS – a note: 

CIRCLE OF WILLIS – a note

SPINAL ARTERIES:: 

SPINAL ARTERIES:

ARTERY OF ADAMKIEWICZ: 

ARTERY OF ADAMKIEWICZ

APPLIED ANATOMY – A WORD: 

Anterior spinal artery syndrome Posterior spinal artery syndrome APPLIED ANATOMY – A WORD

THANK YOU: 

THANK YOU