Abulia: Absence of will power or inability to act decisively
Abulia: Absence of will power or inability to act decisively
Branches of the vertebral, deep cervical, intercostal, and lumbar arteries contribute to three arteries that run the length of the spinal cord; the anterior spinal and the two posterior spinal arteries. The anterior spinal artery arises at the level of the foramen magnum by the junction of two branches, one from each vertebral artery. Each posterior spinal artery arises from the posterior inferior cerebellar artery at the same level. 21 pairs of segmental radicular arteries supply the nerve roots and about half of them contribute to the spinal arteries. Of these larger branches, the largest is the great anterior radicular artery of Adamkiewicz (radicularis magna), which supplies the lower thoracic and upper lumbar parts of the cord. It usually arises from a lower intercostal or a high lumbar artery but may arise as low as L4 or as high as T8 (Figure 4). Since it makes a major contribution to the spinal cord blood supply, spinal injury or aortic surgery may compromise the blood supply of the lower part of the spinal cord. Though the other segmental radicular arteries are small their contributions to the anterior and posterior spinal arteries are important.
Posterior circulation - Applied Anatomy
POSTERIOR CEREBRAL CIRCULATION &BLOOD SUPPLY OF THE SPINAL CORD - Dr.Mohammed Sadiq Azam Final yr. Postgraduate MD (Int Med) Deccan College of Medical Sciences
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
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
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 - 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.
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
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
PCA Syndromes:• Causes: • Atheroma/Emboli @ Basilar • Dissection @ Vertebral • Fibromuscular dysplasia• Two syndromes • P 1 Syndrome • P 2 Syndrome
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… 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 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… 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.
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 – 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
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 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
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
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.
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
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.
PICA• Largest branch of vertebral artery• One of the three major supplies of the cerebellum• Also supplies the lateral medulla• Wallenberg syndrome (=LMS)
MENINGEAL BRANCHES OF VERTEBRAL a.• Posterior meningeal branch• Arises from opposite the formen magnum• Supplies Falx cerebri
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.
LESIONS OF V2 & V3• Atheromatous disease is rare.• Fibromuscular dysplasia, dissection common here• Rarely due to encroachment from osteophytic spurs within vertebral foramina
“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.
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.
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.
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)