tutorials in endovascular neurosurgery and interventional neuroradiology || spinal vascular anatomy

71J.V. Byrne, Tutorials in Endovascular Neurosurgery and Interventional Neuroradiology, DOI 10.1007/978-3-642-19154-1_4, © Springer-Verlag Berlin Heidelberg 2012

Preamble

The spinal blood supply is based on multiple arte-rial pedicles since the primitive spine develops from somites arranged alongside the neural tube. Each somite receives a primitive segmental arterial blood supply from the dorsal aorta. These paired segmen-tal or metameric arteries supply the neural tube, as well as all the constituent tissues of the metamere, i.e. tissue which will differentiate into bone, skin and neural derivatives of the neural crest. The paired arteries persist in the adult pattern as radicular arter-ies and at selective vertebral levels as radiculopial or radiculomedullary arteries. In order to understand the anatomy, this tutorial fi rst considers the embryo-logical development of the spinal blood supply with an emphasis on the arteries. It then describes the adult arterial pattern and fi nally the venous supply. The teaching objective is for a student to learn the sites of arterial pedicles that potentially supply spi-nal pathology and to be able to distinguish normal from abnormal spinal angiograms.

4.1 Embryology of Spinal Arteries

4.1.1 Primitive Segmental Arteries

The spinal cord and brain develop from the neural tube which closes at ca. 3 weeks. The cells of the neural crest form at its margins. They will contrib-ute to the formation of the dorsal root, cranial, autonomic and enteric ganglia, glial cells, Schwann cells, melanocytes, the adrenal glands and parts of

Contents

Preamble .................................................................. 71

4.1 Embryology of Spinal Arteries .................. 714.1.1 Primitive Segmental Arteries ........................ 714.1.2 The Vasa Corona and Longitudinal

Neural Arteries .............................................. 724.1.3 Formation of the Anterior Spinal Artery,

Desegmentation and Multimetameric Arteries .......................................................... 73

4.1.4 Development of Craniocervical Arteries ...... 73

4.2 The Spinal Arteries ..................................... 744.2.1 The Basic Adult Pattern

of Extradural Arteries ................................... 74

4.3 Arterial Supply to the Spinal Cord ........... 754.3.1 Radicular Arteries ......................................... 764.3.2 Radiculopial Arteries .................................... 764.3.3 Radiculomedullary Arteries .......................... 774.3.4 The Anterior Spinal Artery (ASA) ............... 77

4.4 Intrinsic Arteries of the Spinal Cord ......... 784.4.1 Sulcal Arteries ............................................... 784.4.2 Radial Perforators ......................................... 78

4.5 The Extradural Spinal Multimetameric Spinal Arteries ............................................. 78

4.5.1 Arteries Supplying the Cervical Spine .......... 784.5.2 Arteries Supplying the Thoracic Spine ......... 804.5.3 Arteries Supplying the Lumbar Spine ........... 804.5.4 Arteries Supplying the Sacral Spine ............. 80

4.6 Venous Drainage of the Spinal Cord ......... 804.6.1 Veins of the Spinal Cord ............................... 804.6.2 Epidural Venous Plexus

(Internal Vertebral Plexus) ............................ 824.6.3 External Vertebral Plexus .............................. 82

References ................................................................ 82

Suggested Readings ................................................. 82

Tutorial 4 Spinal Vascular Anatomy

72 Tutorial 4 Spinal Vascular Anatomy

the connective tissue of the face, bones of the skull, meninges and teeth. From this stage on, somites differentiate as blocks of mesoderm on either side of the notochord, i.e. developing spine (Fig. 4.1 ).

During the 3–6 week stage, up to 44 pairs may form but some regress, and for our purpose, their development can be considered to comprise the formation of 31 pairs of somites each receiv-ing a metameric artery from the dorsal aorta. These segmental arteries supply tissues derived from the neural tube, neural crest and somite that constitute the metamere, i.e. the precursors of the spinal cord, nerves and paraspinal muscle, skin and bone. Each metameric artery is named after the nerve it accompanies into the neural foramen.

The primitive segmental artery, for each metamere, makes a primary division into postero-medial and posterolateral branches. The postero-medial division supplies the neural tube, neural crest and dorsal epimere (i.e. that part of the somite which contributes to the vertebral column and paraxial muscles). The dorsolateral division supplies all the other structures of the metamere. At its cranial extent, the dorsal aorta contributes

to the carotid arteries and at its caudal extent becomes the median sacral artery.

4.1.2 The Vasa Corona and Longitudinal Neural Arteries

The blood supply to the neural tube develops from a primitive vascular plexus on its surface called the vasa corona. On the ventral surface of the neu-ral tube, a pair of longitudinal channels is formed on either side of the midline from longitudinal connections within the vasa corona. In Tutorial 1 , when they developed anterior to the hindbrain, we called these the longitudinal neural system (LNS), though in the spine they are often called ventral longitudinal arteries. They run on either side of the developing median sulcus. As the cord devel-ops, they give sulcal branches to the spinal cord and branches to the vasa corona (Fig. 4.2 ).

The primitive segmental dorsomedial branches to the ventral neural tube supply the anterior spi-nal roots and the LNS. The branches to the dorsal neural tube supply the dorsal vasa corona and the posterior roots. Posterior longitudinal channels

Neuraltube Neural

crest cells

Notocord

Somite(mesoderm)

Somite(mesoderm)

Neuralcrest cells

Fig. 4.1 Closure of the neural tube and differentiation of somites (Published with kind permission of © Henry Byrne, 2012. All rights reserved)

734.1 Embryology of Spinal Arteries

on the dorsolateral surface of the neural tube form later from the plexus of vessels forming the vasa corona and subsequently develop into the posterior spinal arteries (PSA). The delay is because the ventral LNS supplies much of the grey matter within the cord which precedes the formation of white matter tracts.

4.1.3 Formation of the Anterior Spinal Artery, Desegmentation and Multimetameric Arteries

Craniocaudal midline fusion of the LNS occurs after 6 weeks and creates the anterior spinal artery (ASA). Failures of fusion are more often evident in the cervical spinal cord and represent a failure of maturation of this system. They are evident as apparent duplications of the anterior spinal artery in the adult pattern.

At the same time (6–12 weeks), desegmenta-tion occurs. This is a process in which most of the primitive segmental arterial supply to the LNS and

vasa corona regresses. Completed, this process leaves only 4–8 ventral segmental arteries supply-ing the ASA and 10–20 dorsal segmental arteries supplying the vasa corona. The rest of the seg-mental arteries supply is to the other metameric tissues, i.e. the nerve root, dura and bone.

Concurrently, longitudinal anastomoses between metameres (i.e. multimetameric arteries) develop around the developing spine. These are tradition-ally identifi ed relative to the transverse processes of vertebra as pretransverse, transverse and posttrans-verse longitudinal anastomoses (Fig. 4.2c ).

4.1.4 Development of Craniocervical Arteries

At this point, we should consider the development of the arterial supply of the cervical spine and the primitive brain together. In Fig. 4.3 , the primitive craniocervical region and upper spine are presented in diagram form. The longitudinal multimetameric arteries in the neck are shown (i.e. vertebral artery,

Epimere (muscle)and

neural crest

Dorso-lateral br.

Dorsalaorta

LNS

Dorso-medialbr.

a

b

Rest of metamere

LNS

cA

B

C

Fig. 4.2 ( a – c ) Development of the spinal arteries after closure of the neural tube. ( a ) Shows the longitudinal neu-ral system ( LNS ), which are the fi rst inter-somite channels to develop. ( b ) Shows the division of the segmental artery to the somite into dorso-medial and dorso-lateral branches. The dorsal-medial branch supplies the neural tube, devel-oping peripheral nervous system with muscle and bone of

the spinal segment. ( c ) Shows the relationship between the inter-segmental anastomoses and a spinal vertebra. A post transverse (e.g. deep cervical a.), B transverse (e.g. vertebral a. and lat. sacral a.), C pre transverse (e.g. ascend-ing cervical a. and intercostal anastomotic a.) (Published with kind permission of © Henry Byrne, 2012. All rights reserved)


ascending cervical artery and deep cervical artery) and the proatlantal arteries.

The adult pattern of seven cervical vertebral bodies arising from eight cervical somites cre-ates the need for the proatlantal artery nomen-clature, as was explained in Tutorial 1 . Eight cervical segmental arteries develop for the eight cervical somites, and the fi rst cervical somitic artery (i.e. the proatlantal artery) lies above the C1 vertebra. This is because the vertebral bod-ies develop between somite levels with the intervertebral disc as the centre of the metamere. Thus, the vertebral body is supplied by two adjacent pairs of somitic (segmental) arteries, and its numbered segmental artery is now better

termed as ‘intersegmental artery’. Also shown are the other longitudinal arteries but not the contributions of the ascending pharyngeal and occipital arteries (see below).

4.2 The Spinal Arteries

4.2.1 The Basic Adult Pattern of Extradural Arteries

A standard vertebra (based on the thoracic/lum-bar levels) with its arterial blood supply arising from the aorta is illustrated in Fig. 4.4 . This shows paired intersegmental arteries running

Hypoglossal

SA3

SA4

SA5

SA6

SA8

SA9

SA10

SA7

C1

C2

C3

C4

C5

C6

C7

T1

T2

Proatlantal 2

Ascending cervical a.

Deepcervicala.

Thyrocervical tr.

Vertebral a.

Costocervical tr.

Subclavian a.

Proatlantal 1

SA1

SA2

Fig. 4.3 Segmental pattern of blood supply to the cervical spine and craniocervical junction. SA somite level, C cervical level (Published with kind permission of © Henry Byrne, 2012. All rights reserved)

754.3 Arterial Supply to the Spinal Cord

posteriorly on either side of the vertebral body. They give short osseous branches to the verte-bral body before dividing into ventral and dor-sal branches. An anterior (pretransverse) interseg mental anastomosis is shown before the division. The ventral branch becomes an inter-costal or lumbar artery. The intersegmental artery (and intercostal artery) is numbered by the rib under which it runs. The dorsal branch gives a spinal branch to the intervertebral foramen and passes under the transverse pro-cess of the vertebra to supply the posterior muscles and bone of the lamina and spinous process.

The spinal artery enters the spinal foramen and gives an anterior epidural branch to take part in the retrocorporeal anastomosis. This sup-plies the bone and dura and anastomoses with its counterpart at the midline. These midline anastomoses occur at disc level and are easily recognised by a hexagon pattern (created by longitudinal and horizontal arteries) on angiog-raphy. It refl ects the developmental origin of the vertebral body and its blood supply from two pairs of intersegmental arteries. The spinal

artery also gives a posterior epidural branch to the prelaminar anastomosis and supplies the dura and bone of the lamina. The prelaminar anastomosis is usually smaller than the retrocor-poreal anastomoses with fewer interseg mental anastomoses, but any longitudinal component lies close to the midline and should not be mis-taken for the anterior spinal artery. The spinal artery usually then terminates in radicular spinal branches.


The radiculospinal arteries supply the spinal cord and its nerve roots. These arteries were termed ‘radicular’, ‘radiculopial’ and ‘radiculomedullary’ by Tanon [ 1 ] because they individually provide one of three types of supply to the neural tissue. The radicular artery supplies nerve roots only; the radiculopial artery supplies nerve root and pial plexus (white matter), and the radiculomedullary artery supplies roots, pial plexus and cord medulla (grey matter).

1

3

2

Dorsal br.

Spinal br.

Ventralbr. (lumbar or intercostal a.)

3

Post. transverselongitudinal anast.

Pre transverselongitudinal anast.

Antero lateral.intersegmental anast.

Anterior vertebralbody a.

Fig. 4.4 Basic adult pattern of blood supply to a vertebra. 1 anterior epidural branches and retrocorporal anastomo-sis, 2 posterior epidual branches, 3 radicular spinal a.

(Published with kind permission of © Henry Byrne, 2012. All rights reserved)


4.3.1 Radicular Arteries

These represent the minimum contribution to the neural crest of the embryonic segmental system (Fig. 4.5a ). They branch to both anterior and posterior nerve roots and are usually too small to be imaged on angiography. On each side, all 31 segmental (intersegmental) arteries give a radic-ular artery except at C1. They run with the nerve roots medially to the surface of the cord, and

their trajectory refl ects that of the roots, i.e. near horizontal in the upper cervical spine and with an increasing upwards direction in the lower tho-racic and lumbar spines.

4.3.2 Radiculopial Arteries

The radiculopial arteries arise from 10 to 20 of the intersegmental arteries (Fig. 4.5b ). They divide to

Radicular a.

Radiculopial a.

Radiculomedullary a.

Post. lat. spinal a.

Ant. spinal a.

Radicular a.

a

b

c

Fig. 4.5 Distribution of arteries to the spinal cord. ( a ) Radicular artery supply. ( b ) Radiculopial artery supply on left side. ( c ) Radiculomedullary artery supply on left side (Published with kind permission of © Henry Byrne, 2012. All rights reserved)


follow the anterior and posterior nerve roots onto the spinal cord. The posterior radiculopial artery is the larger and supplies the posterior pial plexus which is usually more developed than on the ven-tral cord. The plexus has longitudinal connections but is functionally monosegmental. The postero-lateral longitudinal arteries are usually the most lateral and dominant of the longitudinal channels that constitute the PSA. In the upper thoracic spine (where white matter predominates), a posterior median longitudinal channel may occur, and in the upper cervical cord, a far lateral longitudinal channel arising from the vertebral artery or PICA and running caudally with the spinal accessory nerve is described as the lateral spinal artery.

4.3.3 Radiculomedullary Arteries

These arteries are the segmental supply to the ASA (Fig. 4.5c ). They occur at four to eight levels (mostly in the cervical spine) with the largest at the lum bosacral enlargement and termed ‘the artery of Adamkiewicz’ (usually arising from a pos-terior intercostal artery between T9 and T12, and more often on left than right side) [ 3 ] . They give

radicular branches and contribute to the anterior pial branches, before joining the ASA, with a dis-tinctive hairpin course evident on angiograms.

4.3.4 The Anterior Spinal Artery (ASA)

This artery represents the result of fusion of the embryonic LNS in the midline (Fig. 4.6 ). It runs from the vertebrobasilar junction to the fi lum terminale. Cranially, it arises from two small branches of the intracranial vertebral artery which join in the midline on the surface of the medulla oblongata at the level of the olives. It then runs on the ventral surface of the spinal cord to the conus where it continues as the artery of the fi lum termi-nale. It lies at the entrance of the anterior median sulcus and deep to the anterior median vein. It supplies the anterior two-thirds of the spinal cord and the majority of its grey matter.

It is often only partially fused in the cervical region, where it receives collateral support from the radiculomedullary arteries. It may appear dis-continuous in the upper thoracic region, and lon-gitudinal anastomoses between two or more spinal levels may parallel the ASA. These arteries

Fig. 4.6 Microangiogram of a post-mortem section of the lumbar spinal cord showing superfi cial and intrinsic spinal arteries. The anterior spinal artery ( large arrow ) lies at the entrance of the median sulcus and the posterior and posterolateral spinal arteries are seen on either side of the posterior root entry zone ( arrow heads ). The sulcal

arteries run in the central sulcus to supply the two sides of the cord in a centrifugal distribution ( small arrows ). (Reproduced from Thron A.,Vascular Anatomy of the Spine, Interventional Neuroradiology, Byrne JV. (Ed).Oxford University Press, 2002 p24, with permission)


run deep to the ASA at the entrance of the median sulcus [ 2 ] . The ASA reaches its largest calibre in the lower thoracic canal before contributing to extramedullary anastomoses around the conus with the posterior spinal arteries (arcade of the conus or rami anastomotici arcuati). This anasto-motic ring is the spinal equivalent of the circle of Willis.

4.4 Intrinsic Arteries of the Spinal Cord

In this section, the distribution of arterial branches within the spinal cord is described. These can be separated into a group running on the surface of the cord in the pial network and giving a centrip-etal blood supply and those arising from the ASA and radiating in a centrifugal direction from within the median sulcus. The former are sometimes called external and the latter internal. I think this is confusing and suggest considering them both together as the internal cord arteries.

4.4.1 Sulcal Arteries

These paired arteries arise from the ASA. They run in the median sulcus and each supplies one-half of the spinal cord. They measure 100–250 m m, run to the depth of the sulcus to one side and then branch within the grey matter. Their lateralisation represents the embryonic separation of the bilat-eral LNS which is maintained despite its fusion to form the ASA. They branch within grey matter with a centrifugal radiation pattern and supply the anterior horn, base of the posterior grey matter column (including the dorsal nucleus) and adja-cent white matter (including the corticospinal tracts). The sulcal arteries are said to give longitu-dinal channels between cord levels within the median sulcus, but once they penetrate pia, they probably don’t take part in longitudinal anasto-moses. However, their territory may ascend to a different spinal level because of differences in growth rates of the bony spine and cord. The cord is vulnerable to their occlusion because they are end arteries and because they supply areas of high metabolic demand.

4.4.2 Radial Perforators

These arise from the pial plexus on the surface of the cord and penetrate the pial surface to supply the underlying white matter. They are smaller (ca. 50 m m) with a short straight course. They thus supply the cord in a centripetal pattern and behave as end arteries.

The network has axial and longitudinal com-ponents. The posterolateral arteries are the most conspicuous elements of the latter. The plexus is supported by the radiculopial arteries and branches of the ASA.

Anastomoses between the sulcal (central) and the radial perforating (peripheral) arteries have been demonstrated. These are described as being directed in centro-posterolateral and centro-anterolateral directions, but they are rarely evident in practice.

4.5 The Extradural Spinal Multimetameric Spinal Arteries

This section describes the arteries that contribute to the blood supply in different regions of the spine. Its content repeats some of the previous sections, but this repetition is justifi ed on the basis that it attempts to cover the practical ques-tion of which arterial pedicles need to be studied during selective catheter spinal angiography. It is separated into the major spinal regions for convenience.

4.5.1 Arteries Supplying the Cervical Spine

The cervical spine is supplied by three longitudi-nal multimetameric arteries with additional con-tributions from arteries of the craniocervical junction (Fig. 4.7 ). 1. Vertebral artery. In the neck, the vertebral

artery represents the longitudinal anastomo-sis of the arteries of the transverse processes between C6 and C1. The vertebral artery arises from the subclavian artery at the level of the C7 metamere and ascends to enter the transverse foramen of C6. Its course and

794.5 The Extradural Spinal Multimetameric Spinal Arteries

branches have been described above and in Tutorial 2 .

2. Ascending cervical artery. Arising from the inferior thyroid artery soon after its origin from the thyrocervical trunk, the ascending cervical artery passes in front of the vertebral artery and runs superiorly between the scale-nus anterior and longus capitis muscles. It rep-resents the segmental arteries of the C3–C4 metameres and gives branches to the segmen-tal anastomoses at these levels.

3. Deep cervical artery. This arises from the costocervical trunk and corresponds to the

C5–C6 metameres. The costocervical trunk arises from the subclavian artery distal to the thyrocervical trunk and runs posteriorly to divide into the deep cervical artery and the highest or supreme intercostal artery anterior to the neck of the fi rst rib. The deep cervical artery usually supplies spinal levels from C7 to C3.

4. The occipital and ascending pharyngeal arteries. The spinal cord supply cranial to C3 can be considered as cephalic rather than spinal, though contributions from the ascending pha-ryngeal artery (C2-4) and occipital artery

Deepcervical a.

Costocervicaltr.

Supremeintercostal a.

Ascending cervical a.

Ascending pharyngeal a.

Occipital a.

Lat. spinal a.

VA

ECA

AntPost

C1

C2

C3

C4

C5

C6

C7

Thyrocervical tr.

Fig. 4.7 Diagram of the adult pattern of arteries supplying the cervical spine (Published with kind permission of © Henry Byrne, 2012. All rights reserved)


(C1-2) are partial remnants of the segmental system. The ascending pharyngeal artery gives musculospinal branches in the midcervical region (C4 and C3) and additionally contributes via the hypoglossal artery and the odontoid arcade.

5. Lateral spinal artery. This small branch of the cranial vertebral artery or posterior inferior cerebellar artery contributes with the posterior spinal artery to the pial plexus. It runs lateral to the upper cord and supplies the posterolat-eral axis between C1 and C3 and joins the pos-terior spinal artery at C4 [ 4 ] .

4.5.2 Arteries Supplying the Thoracic Spine

In the upper thoracic spine, the highest or su preme intercostal artery, which arises from the costocervical trunk, supplies a variable number of vertebra from T1 to T4. The T4 level is usually supplied from the aorta, but several variations may occur, with the highest intercostal artery arising from (or some of its branches from) the vertebral artery, the subclavian artery, thyrocervi-cal trunk or from segmental trunks of the bron-chial or phrenic arteries. The rest of the thoracic spine is supplied by eight or nine pairs of poste-rior intercostal arteries. In both thoracic and lum-bar spines, pretransverse and lateral intersegmental arteries are usually evident connecting adjacent posterior intercostal and lumbar arteries.

4.5.3 Arteries Supplying the Lumbar Spine

The cranial four lumbar arteries arise from the aorta, and the L5 level is supplied by the iliolum-bar artery and the median sacral artery. The ilio-lumbar artery arises from the internal iliac artery and runs cranially anterior to the sacroiliac joint, supplying muscle and giving the lumbar branch to L5. The medial sacral contribution consists of small branches to the L5 roots. The lumbar spinal arteries are arranged in a similar manner to the thoracic spinal arteries.

4.5.4 Arteries Supplying the Sacral Spine

The median sacral artery is a small branch of the abdominal aorta that arises from its posterior surface at the level of the terminal division. It runs in the midline over L4 and L5 and the sacrum, to the coccyx and anastomosis with branches of the superior and inferior lateral sacral arteries.

The lateral sacral arteries are the principle supply to the sacral spine. They arise from the internal iliac artery. The superior lateral sacral artery runs cranially to the S2 pelvic foramen and the inferior artery caudally as a trunk ante-rior to the lateral sacrum (i.e. a pretransverse anastomotic artery) contributing branches that enter the S3–S5 pelvic foramen. It terminates at the coccyx.

4.6 Venous Drainage of the Spinal Cord

The venous drainage will be described from prox-imal to distal and divided into the veins of the spi-nal cord and those of the vertebral column [ 5 ] .

4.6.1 Veins of the Spinal Cord

4.6.1.1 Internal Cord Veins The internal venous drainage of the cord is centrifugal with a radiating pattern of venous capillaries. These are distributed symmetrically through the cord and drained to the venous pial plexus on the surface of the cord. From there, drainage is to two longitudinal midline veins—the anterior and posterior median spinal veins [ 5 ] (Fig. 4.8 ). In the lower thoracic cord at the lum-bar enlargement, this symmetry varies with a modest dominance of drainage to central veins in the median sulcus.

Thoracic region: There are two types of anas-tomotic veins between the intramedullary veins. The fi rst are numerous, through too small to see on angiograms, and form connections throughout the cord. The second are termed ‘transmedullary

814.6 Venous Drainage of the Spinal Cord

veins’ and make anterior to posterior anastomo-ses between the anterior and posterior median veins. They are not collecting vessels and thought to conduct blood in either direction in response to intradural pressure changes (i.e. cough veins). They are more numerous in the cervical and upper thoracic cord than in the lower (caudal) cord.

4.6.1.2 Longitudinal Cord Veins The anterior and posterior median veins drain to the internal and external vertebral plexus of veins [ 6 ] . The anterior median vein is continuous

with the anterior medullary vein and thus con-nects cranially with the veins of the posterior fossa. In the cervical and most of the thoracic spine, they are usually single veins, but at the thoracolumbar junction (i.e. enlargement), the posterior median vein forms a series of parallel veins (the posterior venous plexus) and the ante-rior median vein reaches its maximum calibre (up to 1.5 mm). It continues as the vein of the fi lum terminale at the conus and drains to sacral epidural veins, though may run with a sacral root to the sacral plexus.

a b Fig. 4.8 (a) Injected post-mortem specimen of the posterior surface of the spinal cord showing veins of the lower dorsal and conus region. The posterior midline vein ( black arrow ) is discontinuous and the radicular veins are shown making a hair-pin course, similar to the spinal arteries to follow spinal roots ( white arrows ). (b) Radiograph in the venous phase showing the continuous anterior median spinal vein ( large arrow ) and multi-segmental radicular veins ( small arrows ). (Reproduced from Thron A.,Vascular Anatomy of the Spine, Interventional Neuroradiology, Byrne J.V. (Ed). Oxford University Press, 2002 p26, with permission)


4.6.1.3 Radicular Veins These occur at most but not all spinal levels. The anterior and posterior radicular veins are equally numerous. The numbers of radicular veins have been reported as varying from 50 to 15. The latter is probably closer to the number identifi able on imaging. An estimate for the student who likes numbers is 5–8 in cervical, 10 in the upper tho-racic and 1–2 in the lumbar regions. The most radicular veins follow the anterior spinal nerve to piece the dura, but about 40% leave via separate openings (Fig. 4.8 ). They do not occur in associa-tion with segmental arteries, and a larger vein, from the lumbar expansion, is said never to travel with the artery of Adamkiewicz.

Two important things to remember are that the system is valveless, and their transdural course may be up to 1 cm which is thought to act as a one-way valve. The connection between median and radicular veins has a ‘hairpin’ tortuosity, again probably design to act as a one-way valve (anti-refl ux) valve, and this confi guration should not be mistaken for a radiculomedullary artery. The second important feature is that there is a ‘watershed’ in the longitudinal cord drainage at midthoracic level; above which drainage is cra-nial and below caudal. How this is engineered is not completely understood.

4.6.2 Epidural Venous Plexus (Internal Vertebral Plexus)

The veins comprising the epidural or internal ver-tebral venous plexus lie between the thecal lining of the spinal cord and the bony canal. They receive the radicular veins and veins from the vertebral bodies (basilovertebral veins). The plexus is largest anterior (retrocorporeal) to the theca and extends from the skull base to the sacrum. On angiography, the veins have a characteristic hexagonal pattern. The plexus drains to the external vertebral plexus through the intervertebral foramen.

4.6.3 External Vertebral Plexus

The veins form the external plexus, also extend from the base of skull to the sacrum and are valveless. They run on the anterior surface of the vertebral bodies with posterior veins arranged posterolateral to the canal running over the lam-ina. It connects with the azygos and hemiazygos veins via intercostal and lumbar veins. In the neck, the plexus drains to the vertebral vein and deep cervical veins.

References

1. Tanon L. Les arteres de la moelle dorso-lombaire. Paris: Vigot; 1908 (cited by Lazorthes G, Gonaze A, Djindijan R. Vascularisation et circulation de la moelle epinere. Masson, Paris 1973).

2. Thron A. Vascular anatomy of the spine. In: Byrne JV, editor. Interventional Neuroradiology. Oxford: Oxford University Press; 2002. Chap. 2.

3. Adamkiewicz AA. Die Blutgefässe des Menslichen Ruckenmarkes, II: Die Gefässe der Rückenmarksoberfl äche. S B Heidelberg Akad Wiss. 1882;85:101–30.

4. Lasjaunias P, Vallee B, Person H, Ter Brugge K, Chiu M. The lateral spinal artery of the upper cervical spi-nal cord. Anatomy, normal variations, and angio-graphic aspects. J Neurosurg. 1985;63(2):235–41.

5. Gillilan LA. Veins of the spinal cord. Anatomic details; suggested clinical applications. Neurology. 1970;20(9):860–8.

6. Tator CH, Koyanagi I. Vascular mechanisms in the pathophysiology of human spinal cord injury. J Neurosurg. 1997;86(3):483–92.

Suggested Readings

Crock HV, Yoschizawa H. The blood supply of the verte-bral column and spinal cord in man. Vienna: Springer; 1977.

Lasjaunias P, Berenstein A. Surgical neuroangiography, Functional vascular anatomy of brain, spinal cord, and spine, vol. 3. Springer; 1990. Springer-Verlag, Berlin, Heidelberg: New york

Lockhart RD, Hamilton GF, Fyfe FW. Anatomy of the human body. London: Faber and Faber; 1974.

tutorials in endovascular neurosurgery and interventional neuroradiology || spinal vascular anatomy

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