Leo Happel, PhD Professor, Neurology, Neurosurgery, Physiology, and Neuroscience LSU Health Science Center Leo Happel disclosed no financial relationships
Vascular Lesions of the Spinal Cord The vast majority of injuries to the spinal cord ultimately have a vascular etiology Good News/Bad News may be reversible/has to be reversed in time Blood Pressure is extremely important Start here Understanding this vasculature and its dynamics may help prevent or reverse the effects of injury Review of classical anatomy of the arterial blood supply to the spinal cord
Ischemia/Reperfusion Much of the damage happens with reperfusion While time windows can vary widely, the 20 min window seems to appear in several independent studies Neurosurgery 42:3, 626-634, 1998
Classical Anatomy When you think of an infarct it is natural to think of the arterial supply first let s review the arterial supply Correct but not accurate -the difference is significant! Statistics for population Too much emphasis on longitudinal circulation Doesn t account for longitudinal variations due to collaterals
Concept of the Circulation William Harvey 1628 De Motu Cordis Blood flows from the heart to large arteries, to smaller arteries, arterioles, to capillaries UNIDIRECTIONAL!!
Spinal Cord Vasculature I will argue that the blood supply to the cord is thru an arterial PLEXUS not thru simple named arteries I will argue that perfusion changes with the level of cord I will argue that the venous drainage of the cord is very poorly understood I WILL ARGUE THAT THE ANTERIOR AND POSTERIOR CIRCULATIONS ARE NOT ISOLATED
Classical Anatomy Illustrates source from vertebrals What would an ASA lesion at cervical levels produce??
Watershed areas Anterior 2/3 of cord perfused by anterior spinal artery Posterior 1/3 perfused by the posterior spinal artery
THERE IS NO VASCULAR LESION OF THE SPINAL CORD THAT PRODUCES THIS EXACT PATTERN OF LOSS OVER THE LENGTH OF THE CORD Watershed areas
What is the target of blood flow to the spinal cord? NEURONS & SYNAPSES! The metabolic demands of neurons and synapses is far greater than that of axons Blood flow to neuronal tissue is 10X that to axonal tissue We currently view the spinal cord as 2 vascular beds one anterior and one posterior THIS IS NOT ACCURATE Histologically it is more accurate to view the spinal cord as 3 vascular beds Cervical enlargement, Lumbar enlargement, and Thoracic cord. These also have centrifugal and centripetal distribution What difference does it make? A LOT!
We normally think of blood flowing in one direction through a given artery proximal to distal (Harvey) Not so for ASA there is no proximal or distal due to collateral feeders provide for BILATERAL FLOW at T11 level Doppler flow studies show blood flow in ASA is CAUDAL TO ROSTRAL in most normal individuals Most blood is coming from below
Cross Section, High Cervical Centripetal vessels supply periphery Centrifugal (Ventral Sulcal) vessels supply core, mostly ventrally Central Cord Syndrome Blood supply changes longitudinally Cross-connections between anterior and posterior arteries at every segmental level
Rotation; derotation risks
Regional Demand for Blood The demand of the spinal cord for blood varies by level Collateral flow Transition zones Flow from below
Pattern of centrifugal vessels changes longitudinally Central cord syndrome at different levels will have a different character At cervical and lumbar levels centrifugal perfusion is more directed toward anterior gray cell column and less posteriorly At thoracic levels centrifugal perfusion projects further posteriorly Corticospinal tract blood supply is more vulnerable at thoracic levels because blood is not being directed anteriorly
Clin Anat 8: vol 5, 347-51; 1995
The diameter of the ASA varies greatly along its length Cadaver Material accurate? How to make this more accurate
X.S. area! Thickness of muscular wall! Lumbar blood flow CANNOT be coming from above In most normal pts blood flow in ASA at T11 is caudal to rostral ASA at different levels
What is the evidence that supports a different view of spinal blood flow? Cervical radicular injuries that lead to quadriplegia PSA injuries that lead to quadriplegia Unilateral ASA lesions Recent anatomical studies Post-spine surgery deficits that surgeons simply can t explain ( I didn t DO anything! )
ASA Syndrome is RARE Spinal cord injury rarely occludes ASA Sulcal penetrators are commonly affected. These may be unilateral or bilateral
Sulcal Arteries Extremely Important!!!!! Sulcal penetrators are the start of TERMINAL CIRCULATION THERE ARE NO COLLATERALS FROM THIS POINT ON!!!!!!
How many here would request blood pressure be elevated when significant loss of function is apparent? If vasospasm is the culprit that compromises blood flow through sulcal penetrators higher blood pressure may help However, if sulcal penetrators are damaged and a central cord syndrome is produced THERE MAY BE NOTHING THAT CAN BE DONE TO REVERSE THE PROBLEM
Lumbar enlargement There may be extensive overlap of perfusion in the posterolateral cord
Volume of collateral vessels Significant feeders may go down to L2 Collaterals are crossfeeds between anterior and posterior arteries Collateral change with age Infants have far more collaterals decrease with age
Lumbar cord Penetrating branches from ASA dive into ventral sulcus NO COLLATERALS May distribute unilaterally Considerable individual variability
ASA Variability These are the patterns of degeneration following vascular lesions of the spinal cord Individual variation Variation along the length of ASA
Anterior and Posterior Medullary Arteries Not Equal Perfusion is Complex; Not According To Harvey
Blood Flow in ASA is Bidirectional!! Neurosurg Clin North Am vol 10; No1, pp9-17, Jan 1999 Spinal cord has an arterial PLEXUS
Arterial Conclusions: What has been called ASA Syndrome probably isn t it s sulcal Central Cord Syndrome Posterior Spinal Arteries are important for motor function Collaterals (Radicular) arteries are VERY important Primary blood flow in ASA comes from below at low lumbar levels Now let s look at the venous system -
Spinal Cord Venous System
Batson s Plexus Spinal cord venous system: Valveless In parallel with vena cava & interconnected 200-1000 cc From ophthalmic veins to sacrum Connects with spinal cord veins Important in vascular lesions of cord! Important in spread of metastases, infection, emboli
Veins are far more delicate than arteries Effect of venous congestion stasis Venous congestive myelopathy
Venous Drainage Does Not Follow Arterial Supply
Conclusions: Vascular supply of the spinal cord is unique May be associated with bizarre phenomena Both the arterial and venous circulation follow the pattern of a plexus and do not follow the principles of Harvey
I-Told-You-So METER