J Neurosurg Spine 5:440–442, 2006
Anatomical relationships between the V2 segment of the
vertebral artery and the cervical nerve roots
SERGIO PAOLINI, M.D., AND GIUSEPPE LANZINO, M.D.
Università degli Studi di Perugia, IRCCS Neuromed, Pozzilli, Italy;
and Department of Neurosurgery, Illinois Neurological Institute,
University of Illinois College of Medicine at Peoria, Illinois
Object. During surgical procedures focused on the cervical nerve roots, the surgeon works in proximity to the V2
segment of the vertebral artery (VA). Depending on the specific surgical approach, it may be necessary to identify,
expose, or mobilize the artery. In most cases, the artery may be left undisturbed. To reduce the risk of iatrogenic injury to the V2 segment during anterior and anterolateral approaches to the cervical spine, the authors analyzed the
relationship between the V2 segment and the proximal segment of the C3–6 nerve roots.
Methods. Six cadaveric cervical spines (12 sides) were fixed with formalin, injected with red and blue latex, and
investigated intraoperatively using different magnifications (3 3–40).
The VA rested on the anteromedial surface of the cervical nerve roots at the level of each intertransverse space. The
exiting nerve roots intersected the VA at a distance ranging from 4.5 to 8.1 mm (mean 6.3 6 1.06 mm) from the dural
sac. The distance was slightly shorter at cephalad levels, suggesting that the artery is more posteriorly and medially situated at those levels. Arterial pedicles anchored the VA to the cervical nerve roots at various levels. These arteries gave
rise to purely radicular, ligamentous, and medullary branches without a predictable pattern. After reaching the nerve
roots on their lower margin, the nonligamentous branches pierced the radicular dural sheath within the neural foramen
at a distance of 2 to 4 mm from the VA.
Conclusions. Proximal-to-distal dissection of a cervical nerve root may proceed with relative safety for at least
4 mm. The V2 segment of the VA gives rise to at least one radicular arterial pedicle between C-4 and C-6. These
trunks give rise to purely radicular, ligamentous, and medullary branches in an unpredictable pattern.
KEY WORDS • cervical spine • spinal nerve root • vertebral artery • spinal surgery
T
VA is traditionally divided into four portions.
The V2 segment extends from the VA entry into the
C-6 foramen to the transverse foramen of C-2. It is
the longest segment of the VA and is, for the most part,
embedded within its own osseous canal, in close relationship with the exiting cervical nerve roots. The V2 segment
itself is rarely the target of a surgical approach.2 However,
in a number of commonly performed procedures such as
cervical corpectomy, cervical foraminotomy, and anterior
discectomy, the surgeon works very close to the V2 segment. Although rare, direct injury of this portion of the VA
during cervical surgery is a well-known complication.4
Several investigators have detailed the basic anatomy of
the VA.7–9 However, little attention has been given to the
mutual relationships between the VA and the exiting cervical roots. In this study, we investigated the specific features of the neurovascular complex formed by the second
segment of the VA and the related cervical nerve roots.
HE
Abbreviations used in this paper: VA = vertebral artery; VB =
vertebral body.
440
Materials and Methods
Six cadaveric cervical columns (12 sides) were fixed with formalin, kept in a 60% alcohol solution, and then injected with red and
blue latex. The V2 segment of the VA was investigated under different magnifications (3 3–40). The artery was exposed in a stepwise
fashion, within its own canal, from an anterolateral direction. The
dural sac and the cervical nerve roots were uncovered by a progressive, radical drilling of the VBs and of the transverse processes,
while the VA was left in situ. The distance between the nerve root
axilla and the point where the VA intersects the root itself was recorded, and the relationships between the nerve roots and the collateral branches of the V2 segment were described.
Results
The VA was found to have a close relationship with the
cervical nerve roots. At the level of each intertransverse
space, the posterior surface of the artery rested on the anteromedial aspect of the nerve roots (Fig. 1A). The nerve
roots exiting at C3–6 intersected the V2 segment at a distance ranging from 4.5 to 8.1 mm (mean 6.3 6 1.06 mm)
from the dural sac, as measured on the side of the nerve
axilla (Fig. 1B). The distance was slightly shorter at cephJ. Neurosurg: Spine / Volume 5 / November, 2006
Relationship of the vertebral artery and cervical nerve roots
FIG. 1. Intraoperative photographs. A: A cadaveric specimen showing the relationship between the V2 segment of
the VA and cervical nerve roots after complete unroofing of these structures. Because of the oblique direction of the proximal nerve roots, the posterolateral aspect of the VA rests on the anteromedial aspect of the nerve roots. A radiculomedullary trunk (Rad. Tr.) arises at the C-5 nerve root. At the C-6 nerve root, a purely radicular branch (Rad. Br.) is present. At the C-3 nerve root in this specimen, as in most, there is a typical pair of facing branches: a medial ligamentous
branch supplying the retroodontoid arterial arch (Med. R.Od. Br.) and a lateral recurrent branch (Lat. Rec. Br.) for the
first nerve roots. B: The V2 segment and cervical nerve roots after partial unroofing. This view highlights the relationship of these structures with the VBs and the neighboring osteomuscular boundaries. The interval between the dural sac
and the VA was measured in all the specimens along each nerve root (dotted arrows). C: The cervical neural foramen
after selective unroofing. A radicular trunk bifurcates into a ligamentous branch (Lig. Br.) that leads to the posterior longitudinal ligament (PLL) and a radicular branch, which immediately pierces the radicular dural sheath. The radicular
trunk originates below the nerve root (N.R.) and enters the neural foramen in an ascendant course. A.Tub = anterior tubercle; I.M. = intertransversarii muscles; L.Cap.M. = longus capitis muscle; Tr.B. = transverse bar; VP = venous plexus.
alad levels (Table 1). The exiting roots at each level were
surrounded by extensive venous plexuses (Fig. 1B). These
venous channels were uniformly distributed along the entire length of the exiting nerve root, forming a direct communication between the epidural venous plexus and the
venous plexus surrounding the VA.
Collateral branches arose from the medial and posterior
sides of the VA. The medial branches were directed to the
anterior longitudinal ligament and the VBs. These tiny
vessels were observed in 21 (58%) of the 36 examined
levels and were normally covered with the bellies of the
longus colli and longus capitis muscles. Radicular trunks
arose from the posterior surface of the VA between C-4
and C-6 in 14 (39%) of the 36 levels examined. These medially directed branches left the VA at the inferior margin
of the corresponding nerve root, entered the neural foramen with an ascendant course, and followed the nerve
root with variable branching patterns. In each specimen,
these radicular branches supplied the corresponding nerve
root. In six of 14 cases, the radicular trunk sent a collateral branch into the virtual space between the posterior longitudinal ligament and the VB. In nine of 14 cases, the raJ. Neurosurg: Spine / Volume 5 / November, 2006
dicular trunk concluded at the spinal cord as a contributor
of the anterior or the posterolateral medullary axes (Fig.
1C). In each case, the radicular branches pierced the dural
sheath of the corresponding nerve root within the neural
foramen at a distance ranging from 2 to 4 mm from the VA
trunk.
At the C-3 level, the V2 segment of the VA consistently
gave rise to a medial branch for the retroodontoid arterial
arch and a lateral branch that crossed the extraforaminal
portion of the cervical nerve roots and united with the ascending cervical artery (Fig. 1A). No medullary branches
were observed at this level.
Discussion
Vertebral artery injury is a potential complication of a
number of commonly performed surgical procedures involving the cervical spine. The likelihood of injury is particularly high in the late phase of these procedures, during
the attempt to accomplish thorough decompression of a
nerve root or removal of the most lateral portion of a normal or diseased VB.4 Smith, et al.,11 in a review of 5 years
441
S. Paolini and G. Lanzino
TABLE 1
Length of cervical nerve roots measured from the dural sac
to the medial border of the second segment of the VA
in 12 cadaveric specimens*
Conclusions
Length of Nerve Root (mm)
Specimen No.
C-3
C-4
C-5
C-6
1
2
3
4
5
6
7
8
9
10
11
12
4.5
5.1
4.9
5.2
4.6
4.5
5.2
5.3
5.0
4.9
5.4
5.4
4.9
6.9
6.3
4.9
5.8
6.4
5.6
6.2
6.7
6.2
6.6
7.2
6.4
7.1
6.3
6.8
6.1
5.7
6.3
6.9
7.5
6.5
6.9
7.7
6.5
7.0
6.9
6.8
7.7
6.0
6.4
8.1
8.0
7.1
8.0
7.9
* The mean length was 6.3 6 1.06 mm (6 standard deviation).
of experience with VA injury during anterior decompression of the cervical spine, have reported that the most
common causes of VA laceration were drilling off the
midline, excessive width of bone and disc removal, and
abnormal softening of the lateral bone resulting from
either tumor or infection. Several authors have described
the quantitative anatomy of the VA as it relates to surrounding structures such as the lateral wall of the VBs,5
the uncovertebral joint,1,9 the medial margin of the longus
colli muscle,5,7 and the anterior margin of the VB.7 These
osseous and muscular landmarks, however, are not always
within the surgeon’s view during a lateral decompression.
Moreover, depending on the specific case, the landmarks
themselves might have been removed or displaced in an
early stage of the surgical procedure. In our opinion, one
of the best guides for understanding the position of the VA
during decompression of a cervical nerve root is the nerve
root itself. Therefore, we measured the length of the segment of each nerve root between the dural sac and the VA.
The distance was slightly shorter at cephalad levels because the second segment of the VA is more posteriorly
and medially located at those levels.7 A thorough lateral
decompression can be performed with relative safety by
taking into account, for each level, the length of the free
nerve root before the arterial intersection (Table 1).
The cervical nerve roots receive most of their blood
supply from the second segment of the VA and occasionally convey medullary branches toward the spinal cord.
As shown in this study, radicular trunks are normally present between C-4 and C-6, and, in most patients, at least
one of these trunks eventually gives rise to a medullary
branch. Our observation is consistent with other studies in
concluding that the level of origin of spinal cord branches
is not predictable.6,8 Radiculomedullary branches are
traceable only along a short foraminal segment of the corresponding nerve root, before they penetrate the dural
sheath of the root itself. Therefore, these arteries are usually not exposed by extradural approaches to the cervical
spinal cord. However, their presence should be taken into
account during lateral approaches to the cervical neuroforamen or during any lateral approach to the second seg442
ment of the VA, particularly if dissection or transposition
of the artery is anticipated.3,10,12
The cervical nerve roots intersect the VA at a variable
distance from their origin. Overall, dissection of a nerve
root in a proximal to distal direction can proceed with relative safety for at least 4 mm. In all specimens examined,
at least one radicular arterial pedicle was present between
C-4 and C-6. These trunks give rise to purely radicular,
ligamentous, and medullary branches in an unpredictable
pattern. This information is useful in minimizing the risk
of vascular complications during cervical spine surgery.
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Manuscript received January 22, 2006.
Accepted in final form July 27, 2006.
Address reprint requests to: Giuseppe Lanzino, M.D., Department of Neurosurgery, Illinois Neurological Institute, University of
Illinois College of Medicine at Peoria, 530 Northeast Glen Oak,
Peoria, Illinois 61637. email: [email protected].
J. Neurosurg: Spine / Volume 5 / November, 2006