Development this abbreviated, important sectionprecedsdiscussion of adult anatomy. A more complete discussion is found in the dedicated section of neurovascular embryology.
The basicarrangementof the spinal system consists of ametameric grid of trasversely oriented segmental vessels, connected by various longitudinal channels. This simple bit of knowledge goes a long way in understanding spinal anatomy. Millions of years of speciation have taken place upon a basic building block of the organism the metameric segment. Just like the fly and the worm, the human body consists of metameric segments, with ecto-, meso-, and endodermal elements. Each vertebral body, its ribs, muscle, nerves, and dermatome, correspond to one level or segment. It is perhaps easiest to appreciate this concept at the thoracic level, where each rib, vertebral body, and other elements constitute the prototyical segment. In the early human embryo, the neural tube is first supplied by simple diffusion. When its limits are reached (200 micrometers perhaps), a primitive vascular system consisting of paired dorsal and ventral aortae (longitudinal vessels) and transversely oriented segmental arteries come into play to vascularize the developing tissue of the embryo.
As the tissue of spinal cord continues to enlarge, new longitudinal connections form between the transverse segmental arteries, most likely to facilitate distribution of blood within the vascular system. This pattern is seen throughout the body, but is somewhat easier to recognize in the vertebrospinal arterial system, where it gives rise to adult anterior spinal artery and numerous extradural longitudinal segmental connections which will be discussed below.
Gradual establishment of dominant longitudinal vessels leads to regression of most transverse segmental arteries, except at some levels where such vessels persist in supplying the longitudinal artery.
This process, in terms of the spinal cord, gives rise to the familiar adult appearanec of the anterior spinal artery and its remaining radiculomedullary feeders, while most segmental arteriespreviouslyconnected to it in early fetal life are limited to supply of the nerve root and adjacent tissues in the adult.
The same pattern of development takes place in the extra-axial, paravertebral space, where longitudinal connections between segmental arteries form a multitude of adult vessels, such as the vertebral, pre-vertebral, pre-transverse, deep cervical, lateral spinal, and other arteries, as will be illustrated below.
Adult Vertebrospinal Arterial Anatomy
The basic arterial vertebrospinal vascular unit consists of two segmental vessels, left and right, arising from the dorsal surface of the aorta. The vessel curves posterolaterally in front of the vertebral body, and sends small branches into its marrow. In front of the transverse process, the segmental artery bifurcates into a dorsal branch and an intrercostal branch. The intercostal segment supplies the rib and adjacent muscle and other tissues. The dorsal branch feeds the posterior elements and, via the neural foramen, sends branches to supply the local epidural and dural elements, as well as a radicular artery to nourish the nerve root. At some levels, the radicular artery is enlarged because, instead of supplying local neural elements, it maintained its embryonic access to the anterior spinal artery. At this level, the artery is called radiculomedullary because it also supplies a large segment of the spinal cord. Various other arrangements are seen, for example when radicular artery supplies portions of the dorsal spinal cord, a discontinuous network which is often misrepresented in venerable anatomical texts as a continuous system of two posterior spinal arteries. This is the basic arrangement of spinal supply.
The system varies in the cervical, upper thoracic, and sacral segments (i.e. exceptions are greater than the rule) but the basic principle of segmental dural and radicular vessels supplying neural tube elements is a very useful guide. Variation comes chiefly in form of segmental vessel origin whereas descending aorta serves this puprose for most thoracic and lumbar segments, the vertebral artery, subclavian branches (costocervical trunk for example), supreme intercostal artery, and median sacral artery (effectively a diminuitive continuation of the aorta below the iliac bifurcation) play this role at the appropriate segments. These vessels of origin are part of the gridline of longitudinal channels which form to connect embryonic segmental vessels. For example, the vertebral artery represents a confluence of discontinuous embryonic channels termed the longitudinal neural system into a single trunk. This, in part, explains multiple variations and duplications encountered in the vertebral territory.
Figure 1: Somatotopic organization of the vertebrospinal arterial vasculature, highlighting segmental vascular organization of the vertebrospinal axis and homologous longitudinal anastomoses along its entire length.
As you can see, numerous longitudinal vessels exist throughout the vertebrospinal axis, often with the same vessel going by several different names, for historical reasons. For example, see above for homology between the lateral spinal, pre-transverse, and deep cervical arteries. The segmental arrangement is particularly modified in the cervical region, where longitudinal vessels are dominant most obviously the vertebral arteries. It is important however to recognize the existence of segmental vessels connecting the three dominant cervical longitudinal arteries (ascending cervical, vertebral, and deep cervical) in terms of their anastomotic potential and its implications for both collateral revascularization and inadvertent embolization during interventional procedures.
The following diagrams provide a basic view of relevant arterial anatomy of the spinal elements, serving as a guide for interpretation of subsequent catheter angiography illustrations.
A aorta; B segmental artery; Ba intersegmental arterial anastomosis; C prevertebral anastomotic network; D direct vertebral body feeding arteries; E dorsal spinal artery; F intercostal/muscular artery; G pretransverse anastomotic network; H dorsal division of the dorsal spinal artery; I post-transverse anastomotic network; J muscular branches of the post-transverse anastomotic network; K ventral division of the dorsal spinal artery; Ka radicular artery; La ventral epidural arcade; Lb dorsal epidural arcade; M nerve root sleeve dural branch of the ventral division dorsal spinal artery; N dural branch of the ventral division dorsal spinal artery; O radiculopial artery; P radiculomedullary artery; Q anterior spinal artery; R mesh-like pial arterial network; S, T posterior spinal artery; U, V pial arterial network (a.k.a. vasocorona) anastomoses between anterior and posterior spinal arterial systems, W sulco-commissural artery, X rami perforantes of the peripheral (centripetal) system, Y central (centrifugal) system of sulcal arteries, originating from pial network of the cord; altogether, the pial network and rami perforantes (R+Y) are called the vasocorona or corona vasorum; Z rami cruciantes (a.k.a. crux vasculosa, a.k.a. rami anastomotici arcuati)
In the following examples, nomenclature using the above letters will be used for correlation.
Aorta and segmental vessels. Many spinal angiogramsstart with imaging the biggest vessel in the body. Some are surprised to discover that these segmental lumbar and intercostal arteries (red)are actually not that small (between 1 and 2 mm diameter typically) most can be easily engaged (and occluded) with a 5F catheter. The aortic injection gives a roadmap, may identify a particularly large fistula, and show which levels may have missing segmental arteries, thereby obviating a frustrating search. In this angiogram of a patient with a dural fistula, a congested spinal cord vein (light blue) can be seen in the venous phase (dark blue). Celiac trunk (orange) and renal arteries (yellow) are also labeled.
Typical Lumbar artery (segmental artery) injection. During spinal angiography, the segmental artery is selected with an appropriate 4F or 5F catheter (RDC, SAS). Injection rates are 1-2 cc/sec for as long as you think you need it, typically 2-4 seconds. Frame rates vary from 1-3 per second, and should not exceed 3 unless particularly necessary (to visualize microanatomy of a high flow fistula, for example). When dural or other fistula is suspected, multiple levels may need to be interrogated. One can easily go through 300 ml or more of contrast, so be aware. For metastatic disease, the search may be more focused. It is helpful to view the angiogram in both subtracted and native views to appreciate both fine vascular detail and bony landmarks.
The lumbar artery (purple, B)is relatively selectively injected, with trace opacification of hte contralateral left L3 lumbar artery due to proximity of the left and right orifices to each other. Since there is no rib, the artery does not have a prominent intercostal component. The arteries of the dorsal branch (red, H, J) supply the lamina and adjacent tissues, with anastomosis to the spinal process arterial arcade (yellow, I). You can see continuation of this arcade inferiorly, NOT to be mistaken for the anterior spinal artery or other spinal artery. The anterior spinal artery is straighter and has a characteristic radiculomedullary hairpin turn (see below). A large paravertebral anastomotic branch (green, G) is present, which opacifes ipsilateral L4 level dorsal branches (blue, H, J). No radiculomedullary artery is seen at this level.
Common lumbar trunk: Especially in the lower spine, single left and right lumbar artery origins are common. Absent levels are also common, usually supplied via paravertebral and prevertebral anasomoses.
Paravertebral anastomotic network typically, this is the dominant longitudinal anastomotic connection between adjacent segmental arteries.It is particularly well visualized in young, normotensive patients. Technical considerations are also important having the catheter well-wedged into the ostium of the segmental artery, as well as longer, higher volume injections (within reason, of course), are key to opacifying all kinds of collaterals.The paravertebral network is located along the lateral aspect of the vertebral body, adjacent to the sympathetic chain, for example. A well developedparavertebral network (blue, G) is present. The catheter (red) is engaged in a lumbar artery (brown, B) and via this network opacifies thelumbar atery of the level immediately above (purple) and immediately below (pink). Notice the spinous process arcade again (black, I). This network ensures virtual impunity for atherosclerotic or iatrogenic occlusion ofa proximal segmental artery. More care should be excersized at radiculomedullary artery levels.
Multiple longtitudinal anastomotic networks prevertebral, paravertebral, spinous process
In this patient, all three networks are demonstrated stereoscopy is very helpful to decide which is which. Also notice prevertebral transverse and retrocorporeal networks at same level.
C prevertebral anastomotic network; G paravertebral anastomotic network (can opacify adjacent levels with strong injection, or supply adjacent level in case of intercostal artery hypoplasia/aquired stenosis);I spinous process branch and associated anastomotic network connecting spinous processes; Blue precorporeal anastomotic network (not shown in diagram); blue retrocorporeal anastomotic network (pink color vessels in diagram, and see section below); light blue left L1 segmental artery; brown left T12 segmental artery; dark green right T12 segmental artery; pink radiculopial artery.
Another demonstration of multiple longitudinal anastomoses:
Lumbar segmental artery injection, demonstrating a well-developed post-transverse anastomotic network (I) visualized through the ventral division (H) of the segmental artery (B), with its muscular branches (J), as well as the pre-transverse anastomosis (G), both contributing to collateral visualization of the adjacent cranial segmental artery (B). F muscular artery, homolog of the intercostal artery.
Retrocorporeal arterial network
This characteristic diamond-shaped network behind the vertebral body (in the epidural space dorsal to the posterior vertebral body cortex, also known as anterior [with respect to the spinal cord] epidural space) marked with L on the diagrams above, constitutes the primary anastomotic connection between left and right segmental arteries of the same level. Like everything, else it is variable in prominence based on developmental and other considerations. A good injection can usually opacify parts of the network, but it becomes quite obvious once the diamond-shaped configuration corresponding to left and right superior and inferior contributors to the diamond are revealed. One way to improve visualization of the network is via an injection adjacent to a dissected segmental artery.
More retrocorporeal arcade images, demonstrated to great advantage in a young patient
T12 segmental artery injection of a young, normotensive slender patient, providing exquisite visualization of the various trans-segmental anastomoses, demonstrating a hexagon-shaped multilevel anterior epidural arcade (La), and prevertebral anastomoses (G). Notice developmental hypoplasia of the right T11 segmental artery (single white arrow, one level above the catheter), with a corresponding small intercostal artery caudal to its normal position (double white arrow). Both radiculomedullary (P) and radiculopial (O) arteries are present, the former demonstrating its characteristic midline course.
Another injection, which happens to preferentially opacify the retrocorporeal network
The median sacral artery continuation of the aorta, the median sacral artery usually comes off the carotid bifurcation, and can be most easily engaged via some kind of recurved catheter (It is the artery to the tail of countless species which happen to have one). As a homolog of the aorta, it gives origin to segmental vessels of the sacrum. Thus median sacral artery injection is in fact a sacral aortogram opacifying multiple segmental sacral branches. It is a must see artery when looking for a fistula. Here, the median sacral artery (red) originates from the left L4 branch (blue and yellow). Lumbar segmental vessels seen on the aortogram are shown in green.
Median Sacral Artery andLateral Sacral Arteries -- the lateral sacral arteries are longitudinal vessels wich are homologous to the paravertebral (pre-transverse) anastomoses in the thoracolumbar segments and to the vertebral artery in the cervical spine. They arise from proximal internal iliac arteries, and can be seen from either internal iliac or median sacral injections, as well-demonstrated below:
Inferior lumbar and sacral anatomy. A stereo pair, B native image, C legends: Selective catheterization of a common L5 segmental trunk (white arrow), also giving rise to the median sacral artery (normally arising from the region of aortoiliac bifurcation). The injection opacifies bilateral L5 and sacral segmental arteries (B), and the prevertebral anastomotic network (G), which is homologous with lateral sacral arteries. A stereo pair; B native image; C Labels.
Here is an injection of the lateral sacral artery (center) with adjacent images of bilateral internal iliac injections, demonstrating existence of extensive collateralization between the internal iliac and median sacral systems by opacifying the same arteries which are labeled with the same color arrows. The purple and red arrows point to the lateral spinal artery seen from both median sacral and internal iliac injections. Green arrows outline the remainder of the lateral sacral system, best seen from medial sacral in this case.
Median sacral artery (purple) giving rise to multiple sacral segmental arteries (red) and to a lumbar artery (yellow)
In this example, median sacral artery arises from a common L5 trunk.
Below the aortic bifurcation, segmental arteries can be visualized by injection of the median sacral artery (above) and internal iliac arteries, via the lateral sacral artery (see figure 1 above) The importance of iliac artery investigation cannot be overstated. The patient whose images are shown below underwent two spinal angiograms for investigation of suspected dural fistula, based on classic MRI appearance of cord congestion and serpiginous vessels in setting of progressive neurologic decline. Only on third time around was the left internal iliac artery interrogated, easily disclosing a dural fistula, supplied by a segmental artery (purple) and collateral probably dural artery (orange) with fistula point (red) and draining into a radicular vein (light blue) connected to the spinal venous network (above, not shown).
ANTERIOR SPINAL ARTERY (ASA): Cervical, thoracic, lumbar, and conus regions.
Overview: the anterior spinal artery (Q) develops as a longitudinal vessels connecting transversely oriented segmental arteries, as discussed at length above. It is located on the ventral surface of the cord, adjacent to the ventral median fissure of the spinal cord. It varies in size, more or less based on the amount of gray matter at the given segment. As such, its size is substantially larger in the cervical and lumbar segments (might be500-750 micrometersin diameter), as compared with slender mid-thoracic size. As such, one end of the ASA has limited to no capacity to support the other should its dominant radiculomedullary supply fail. The arterial supply to the ASA consists of radiculomedullary arteries (P), which represent persistence of embyronic segmental connections between the aorta and the developing ASA. Their number varies, perhaps being 6-10 in the human. Some are quite small and, as such, below resolution of in vivo spinal angiography. The larger cervical and lumbar ASA segments are associated with larger radiculomedullary arteries to supply them the famous artery of lumbar enlargement (Adamkiewicz), and the less well known (radiculomedullary) artery of the cervical enlargement, known to some neurovacular anatomists as the artery of Lazorthes. The Lazorthes most commonly arises from lower cervical vertebral artery, though not infrequently from deep cervical or supreme intercostal vessels also. The Adamkiewicz comes off between T9 and T12 in 75% of cases,more commonlyon the left (which means, to me, that 1/4 of the time, its somewhere else). Not infrequently, there are two relatively smaller radiculomedullary arteries at the lower thoracic spine, instead of one big Adamkiewicz. At the bottom of the cord, the anterior spinal atery is typically connected to posterior spinal arteries (T) via what paired arteries (Z) which go by many names (such as rami cruciantes), forming a kind ofarterial basket (see above diagram, and below for angio images). Visualization of this basket is critical if you wish to call a spinal angiogram complete.
Cervical ASA:
Bilateral vertebral artery study in anterior spinal artery supply. Sometimes, in intracranial work, it becomes important to know the location of the anterior spinal artery with respect to the cervical spine. For example, vertebral artery dissection may be treated differently depending on whether it involves ASA origin. Vertebral artery sacrifice should not be undertaken until the location of the ASA has been considered. For example, closing a vert immediately distal to radiculomedullary ASA contribution, without other runoff branches, risks possibility of the vert stump thrombosing back and closing this ASA segment. Collaterals are often insufficient to maintain cord viability.
Just seeing one radiculomedullary ASA contributor may not be enough in some cases to truly define full anatomy one must opacify the entire ASA system. If a given radiculomedullary artery only shows the ASA inferior to its level, then one must keep looking for additional rostral sourses. For example, if one sees an ASA from C5 down in a case where ascending or deep cervical embolization is required, it would be advisable to find the source of superior cervical supply before concluding that ASA territory is safe. In this case, the upper cervical cord segment is supplied from the left C5/6 level, while the inferior cervical cord from the right C4/5 segment.
Left vertebral (top) and right vertebral (bottom) set of images from the same patient, demonstrating full length of cervical anterior cerebral artery supply from the vertebral system. The lower portion of the cervical ASA (red, Q) is fed via the left C5/6 radiculomedullary contributor (yellow, P), which also happens to supply the posterior spinal artery network (purple, S, T). The upper ASA segment is fed by the right C4/5 radiculomedullary artery (yellow, P) seen on the image below. The radicular portion is labeled in yellow. ASA=red; Posterior spinal arteries = purple
Another view of cervical radiculomedullary artery (of Lazorthes) arising from inferior vertebral (C6 segment). This kind of dominant supply is seen less frequently for the cervical spinal cord than it is for the thoracolumbar enlargement in case of the artery of Adamkiewicz.
A, B Frontal and C lateral stereo pair projection digital subtraction and native angiographic views of right vertebral artery injection, visualizing a dominant cervical radiculomedullary artery (P, artery of Lazores) and the anterior spinal artery (Q), anastomosing with its basilar homolog (long white arrowhead). Very faint posterior spinal artery (T) is best seen in stereo, as well as the lateral spinal artery (short white arrow).
Another view of the cervical cord, this one also displaying the posterior spinal (brown) axis and the pial vessels (yellow) which connect the anterior and posterior axes on the pial surface of the cord. Visualizaton of the pial network of the thoracolumbar cord is limited by the body habitus of the patient, which works against resolving small vessels even under conditions of perfect paralysis and apnea. The situation is much better in the cervical spine. Notice the discontiguous nature of the posterior spinal network, in contrast to the straight anterior spinal artery.
Although balanced supply to the cervical cord is more common, and most of the time it comes from the cervical vert, occasionally the typically small distal intracranial vertebral artery supply is dominant, as in this case. It is important to pay attention to this when flow diversion methods are used in the distal vertebral artery.
Lateral view of the same, in stereo
Deep Cervical origin of the radiculomedullary artery second most common after the vert. At our institution, all cases of posterior fossa subarachnoid hemorrhage with no intracranial cause REQUIRE indentification of the anterior spinal artery, as in ~10% of cases (in-house experience) the pathology turns out to be in the cervical spine.
Anterior spinal artery (Q) origin from deep cervical artery, P= radiculomedullary artery; notice collateral opacification of the vertebral artery (long white arrow) via the C2 segmental artery (short white arrow).
Another deep cervical origin any longitudinal system can give origin to the radiculomedullary artery in this case the radiculomedullar artery (orange) originates from the deep cervical branch (red). Notice also injection of supreme intercostal artery (pink, lower two images)with extensive deep servical artery anastomoses (yellow) through which the anterior spinal artery can be inadvertently embolized. The catheter, barely engaged in the supreme intercostal,is labeled in blue.
Same patient, contralateral side, demonstrating tumor blush (hemangiopericytoma) from the right subclavian injection supplied by costocervical (purple) and thyrocervical (orange) branches. An ipsilateral supreme interconstal (red) injection demonstrates extensive additional tumor, which is not apparent from the subclavian injection. The vert is labeled in light blue.
Supreme Intercostal Origin of Cervical Spinal Artery occasionally seen as well, and important to know. The supreme intercostal and upper thoracic arteries can be difficult to catheterize sometimes, especially in patients with capacious dilated atherosclerotic aortas. We use a 4F or 5F RDC (which can be too small for the upper thoracic spine); if that does not work, one can try an appropriately-sized Cobra, or perhaps a Simmons 1. Sometimes, hand-shaping an RDC to produce a bigger curve (so as to push against the contralateral aortic wall) is more helpful than another catheter. In this case, the supereme intercostal was visualized via the T4 segmenal injection through a prominent paraspinal anastomosis (I)
stereo pair, supreme intercostal arteyr origin ofthe anterior spinal artery (same legends as above), visualized via T4 injection through a prominent post-transverse anastomosis (I). Notice transient contrast reflux into a cervical radiculomedullary branch (P); another longitudinal anastomosis (white arrow) between adjacent T3, T4, and T5 segmental arteries
Supreme intercostal artery (redP origin from the vertebral artery another example of homology between various longitudinal anastomoses. Notice multiple intercostal arteries (yellow)
Stereo pairs, demonstrating posterior course of the supreme intercostal artery at the level of dorsal ribs
Thoracic region: The artery of thoracic enlargement (Adamkiewicz) usually comes of T9 throughT12 region. There is often a region of thoracic cord (mid-lower, depending on the Adamkiewitz origin, which is rather small in caliber, relative to the more well-developed cervical region vessel. A watershed of sorts (yellow) therefore exists which occasionally may correspond to cord infarction in states of hypotension. This double catheter injection (done for evaluation of cord infarction in the region of the basket, below the watershed) demonstrates the slender size of mid-to-lower thoracic ASA. Red=ASA; Purple=radiculomedullary arteries
The artery of Adamkiewicz. Typical appearance. Another patient, with stereo views of the radiculomedullary artery.The radiculomedullary artery (pink) often demonstrates a small segment of narrowing at the point where itpierces the dura(white arrow). The intradural segment (blue) opacifies the anterior spinal artery (red). RDC (catheter) is labeled in green.
Radiculomedullopial artery. By definition, the radiculomedullary artery is a radicular artery which supplies the ASA (red). A radiculopial artery is one which supplies the pial (posterior spinal) system (yellow). When one does both (orange), it is called radiculomedullopial. So there
Figure 9 A-D: A early arterial, B late arterial, C native, and D venous phase images. The artery of Adamkiewicz (Ka), originating at left L1 level, opacifies the anterior spinal artery (Q). The force of contrast injection transiently reverses flow in a smaller radiculomedullary contributor (Ka) sephalad of the Adamkiewicz. A faint radiculopial artery (O) from contralateral right L1 level is visualized through the anterior epidural arcade (La). Notice subtle caliber change where the radiculopial artery pierces the dura (short black arrow). D- venous phase image demonstrating expected visualization of spinal vein (e, either anterior or posterior), and the Great Radicular Vein (j), the venous homolog of the Adamkiewicz.
The main contributor to the anterior spinal axis (Adamkiewicz, ) arises from the left T11 level. The tumor can still be embolized from the right T8 level as long as the Adamkiewicz can adequately reconstitute the anterior spinal axis at the level supplied by the right T8 segment. This can be determined by Balloon Test Occlusion of the right T8 radiculomedullary artery while injecting the level of the Adamkiewicz. The decision is made on angiographic basis as the patient is asleep and, in my opinion, the exam is too unreliable in the time span of the BTO. If the patient passes BTO, the right T8 radiculomedullary artery is closed (very tightly) with coils, and the tumor can then be embolized (particles). So, below is an injection of the left T11 Adamkiewicz (pink) with balloon inflated in the right T8 ventral division (black). Notice amazing visualization of the anterior spinal axis (white), with contrast reflux into the radiculomedullary arteries at the right T8 level (light blue) and left T10 levels (dark blue). Also extremely well seen are long contiguous segments of the posterior spinal artery on the right and somewhat shorter but still quite extensive for the posterior spinal system segment on the left (purple arrows), The PSAs are opacified via the well-seen vasocorona (pial) networks (green), retrogradely visualizing radiculopial contributing vessels (orange). The left T10 level supplies both anterior and posterior spinal arteries, and therefore would be technically radiculomedullopial.
This kind of anatomy is best seen in stereo:
Variant high origin of thoracic ASA. The Adamkiewicz can occasionally (25% of the time) come off unusually high or low. In these cases, there is often variation in terms of posterior cerebral artery anatomy as well. In this patient, a large Left T5 level radiculomedullary artery supplies the ASA (white) of entire thoracic spine. Patients like these are at a somewhat higher risk of cord infarction, having little in the way of collateral radiculomedullary ASA supply. An unusually prominent posterior spinal artery (red) is present also.
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Spinal Arterial Anatomy | neuroangio.org