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Spinal Cord Blood Supply and Its Surgical Implications

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Spinal Cord Blood Supply and Its Surgical Implications Review Article Spinal Cord Blood Supply and Its Surgical Implications Abstract Matthew W. Colman, MD The blood supply to the spine is based on a predictable segmental Francis J. Hornicek, MD, PhD vascular structure at each spinal level, but true radiculomedullary arteries, which feed the dominant cord supply vessel, the anterior Joseph H. Schwab, MD spinal artery, are relatively few and their locations variable. Under pathologic conditions, such as aortic stent grafting, spinal deformity surgery, or spinal tumor resection, sacrifice of a dominant radiculomedullary vessel may or may not lead to spinal cord ischemia, depending on dynamic autoregulatory or collateral mechanisms to compensate for its loss. Elucidation of the exact mechanisms for this compensation requires further study but will be aided by preoperative, intraoperative, and postoperative comparative angiography. Protocols in place at our center and others minimize the risk of spinal cord ischemia during planned radiculomedullary vessel sacrifice. to the spinal cord. Most end within General Structure of Spinal the nerve root, dura, or pial plexus. Cord Blood Supply The radicular arteries that do con- tribute to the longitudinally oriented The spinal cord is nourished by single anterior spinal artery (ASA), a structure of arterial supply that fol- and therefore to the anterior two lows a generally predictable path from thirds of the spinal cord parenchyma, the great vessels to the parenchyma of the white and gray matter are named anterior radiculomedul- 1 throughout the spinal cord (Figure 1). lary vessels. Gao et al demonstrated Segmental vessels originate from the the presence of 72 of these vessels great vessels of the neck, thorax, across 20 human specimens, for an and abdomen at each segmental average of 3.6 per specimen. Con- 2 level and, with few exceptions, are versely, Martirosyan et al cited an paired bilaterally. Although the average of 10 (range, 2 to 17) segmental vessel typically divides throughout the spinal cord. Anterior into an anterior and posterior radiculomedullary arteries are usu- ramus, the posterior ramus is the ally not paired at any given level. dominant vessel and divides further Their end recipient vessel, the ASA, From the Department of Orthopaedic Surgery, Massachusetts General into a muscular branch and a spinal is mostly in continuity throughout 3,4 Hospital, Boston, MA. branch. The spinal branch becomes the entire cord and experiences both anterograde and retrograde J Am Acad Orthop Surg 2015;23: an anterior radicular artery and 581-591 a posterior radicular artery as it flow, depending on the functional demand and location of dominant http://dx.doi.org/10.5435/ traverses the neuroforamen alongside JAAOS-D-14-00219 the segmental nerve root. There are radiculomedullary feeder vessels. 31 paired radicular arteries, one for The ASA gives off many central ar- Copyright 2015 by the American Academy of Orthopaedic Surgeons. each segmental level, but relatively teries, which project and often few of them contribute meaningfully bifurcate in the sagittal plane, October 2015, Vol 23, No 10 581 Copyright ª the American Academy of Orthopaedic Surgeons. Unauthorized reproduction of this article is prohibited. Spinal Cord Blood Supply and Its Surgical Implications Figure 1 ischemic functional deficits when thoughttoberedundantandwell- disrupted. As opposed to the terminal collateralized, significant variation branches of the anterior system, the exists in the number of dominant PSAs supply the cord matter in supply vessels to the ASA, and their a centripetal pattern. Most anatomic number and distribution should be studies have not identified direct well documented before considering anastomotic connections between the surgical disruption. anterior and posterior systems,2 whereas others have observed a con- nection in certain anatomic areas, Structure Unique to the such as around the conus medullaris.1 Thoracic Spine In any case, significant overlap and redundancy does occur between the In the thoracic spine, the segmental terminal supply branches of these two vessels come from the aorta or the systems within the parenchyma of the subclavian artery and continue on as spinal cord itself. intercostal arteries. The number of radiculomedullary arteries in the thoracic spine is fewer than in other Structure Unique to the areas (average, one to four), and they Illustration of typical spinal cord 3 blood supply under normal Cervical Spine are more spread out. There is poor conditions. One radiculomedullary collateral potential in this region, vessel is shown, which supplies the The ASA in the cervical spine takes its and there is virtually no direct anterior spinal artery through origin from two intervertebral ar- communication between the central a hairpin loop. teries at the very upper end of the (anterior) and peripheral (posterior) cervical spine, where it is largest, and systems.4 The ASA of the thora- heading to the center of the cord slowly tapers to a constant diameter columbar spine is fed by one or two matter. These central arteries are for the remainder of the cervical anterior radiculomedullary vessels, most dense in the lumbosacral region and into the thoracic region.7 the most dominant of which is region, followed by the cervical and In the cervical spine, segmental ves- termed the artery of Adamkiewicz thoracic regions. These terminate in sels originate from the vertebral ar- (AA).8 This feeder vessel of the ASA centrifugally oriented, inside-to- teries in the upper portion and, in the can be up to 1.3 mm in diameter and outside capillary beds, which are remainder of the cervical spine, from occurs on the left side between T9 five times as dense in gray as in white the vertebral arteries and deep cervi- and T12 in 75% to 80% of cases.9,10 matter.5 cal, costocervical, or ascending cer- The AA gives off a dominant de- The posterior one third of the cord vical branches. The segmentals then scending branch in a “hairpin” parenchyma is supplied by paired give off anterior and posterior radic- configuration and a much smaller posterior spinal arteries (PSAs), which ulomedullary arteries, the former of ascending branch as it joins the ASA. are fed by the posterior radicular ar- which supply the ASA, as in other The ASA is typically continuous teries. This arterial supply is more regions of the spine. There are typi- throughout the thoracic spine, but its similar to an arterial plexus than to the cally from one to several dominant caliber is significantly attenuated, often-envisioned two longitudinal unilateral anterior radiculomedullary especially as it approaches the paired arteries.6 Generally, these ar- vessels in the cervical spine.1,2 AA.9,11-13 These factors are thought teries are much smaller than the ASA Although the blood supply to the to be responsible for the sensitivity of and are less consequential in regard to cervical spinal cord is generally the thoracic region to ischemic insult Dr. Hornicek or an immediate family member has received research or institutional support from Stryker; has received nonincome support (such as equipment or services), commercially derived honoraria, or other non-research–related funding (such as paid travel) from Biomet; and serves as a board member, owner, officer, or committee member of the American Association of Tissue Banks and the International Society of Limb Salvage. Dr. Schwab or an immediate family member is a member of a speakers’ bureau or has made paid presentations on behalf of Synthes and Stryker Spine; serves as a paid consultant to and serves as a board member, owner, officer, or committee member of Biom’up; and has received nonincome support (such as equipment or services), commercially derived honoraria, or other non-research– related funding (such as paid travel) from Globus Medical and Stryker. Neither Dr. Colman nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this article. 582 Journal of the American Academy of Orthopaedic Surgeons Copyright ª the American Academy of Orthopaedic Surgeons. Unauthorized reproduction of this article is prohibited. Matthew W. Colman, MD, et al of the anterior part of the spinal presentation of cord ischemia ranges involving open TAAA repair may not cord. from complete paraparesis to asymp- be the best model for examining the tomatic transient abnormalities anatomic causes of spinal cord ische- detectable only by neuromonitoring. mia. Endovascular techniques, such as Structure Unique to the The key clinical question driving thoracic endovascular aortic repair, Lumbar and Sacral Spine much of the anatomic research in which selectively excludes specific seg- spinal cord ischemia during surgical mental vessels by way of intra-aortic The tip of the conus medullaris may interventions is which key vessels stents, may be a better model for be nourished by the descending ter- must be preserved to maintain spinal examining the effect of segmental vessel mination of the ASA directly, but there cord perfusion pressure and therefore sacrifice on cord ischemia. In 71 pa- also exists a highly collateralized spinal cord blood flow to avoid func- tients undergoing TAAA endovascular anastomotic network at this location tional deficits. repair, Kawaharada et al20 observed termed the anastomotic loop of the less spinal cord injury in a group in conus.7 The lower lumbar and sacral whom the AA was not occluded by the radicular
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