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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3821_Библиотеки_им_академика_М_И_Перельмана.pdf
Variations oftheVertebral Artery
(VA) andVertebrobasilar Junction
(VBJ)
10
Abstract
This chapter includes (1) Anomalous level of
entry to the transverse foramen, (2) C2 segmental type VA, (3) C3 segmental type VA, (4)
Extracranial and craniovertebral junction VA
fenestration, (5) Intracranial VA fenestration
and VBJ arterial ring, and (6) VA termination
at the posterior inferior cerebellar artery.
There are 15 gures and 3 illustrations.
Before either neck surgery or posterior
fossa surgery, VA variations should be identied to prevent complications.
Keywords
Fenestration · Transverse foramen · Vertebral
artery · Vertebrobasilar junction
10.1 Anomalous Level ofEntry
totheTransverse
Foramen(TF)
It is well known that VA usually enters the C6
TF. The prevalence of entrance at an abnormal
level into the C7, C5, C4, C3 TF is reported to be
0.8%, 5.0%, 1.0% and 0.2%, respectively [1]. As
mentioned in Sects. 1.2 and 1.3, VA origin variations are strongly correlated with variations in the
level of entry to the TF [2]. In the case of direct
origin of the left VA from the AA distal to the left
SA (Sect. 1.2.3), the entry level is the C7 TF
(Fig. 10.1). Both left VA of direct AA origin
proximal to the left SA (Sect. 1.2.1) and right VA
of extreme proximal right SA (Sect. 1.3.1) enter
C5, C4, or C3 TF (Fig.10.2) [3].
10.2 Anomalous Level ofEntry
totheSpinal Canal
10.2.1 C2 Segmental Type VA
The VA normally enters the subarachnoid space
via the superior surface of the C1 posterior arch.
When the VA enters the spinal canal via the C1/2
intervertebral space, this anomalous course of
the VA is called a C2 segmental type VA [4] or
persistent rst intersegmental artery [5]. The latter name seems inadequate, because the rst
intersegmental artery persists and forms a normal VA.Lasjaunias etal. [6] proposed an embryological explanation for this variation (Fig.10.3).
Its prevalence on MR angiography was reported
to be 3.2% [7]. CT angiography is better than
MR angiography for the detailed observation of
this variation, because the bony structure can be
seen simultaneously (Fig.10.4). This variation is
relatively frequently observed bilaterally.
However, because of its symmetric fashion, the
bilateral type may be easily overlooked
(Fig.10.5).
To avoid complications during surgery at the
craniovertebral junction, this common VA varia-
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022
A. Uchino, Atlas of the Supraaortic Craniocervical Arterial Variations,
https://doi.org/10.1007/978-981-16-6803-6_10
131
132
10 Variations oftheVertebral Artery (VA) andVertebrobasilar Junction (VBJ)
a
b
C7
Fig. 10.1 (a) LAO projection of CT angiography shows the left VA arising from the AA distal to the left SA (arrow).
(b) CT angiographic source image at the level of C7 vertebral body shows the left VA in the left TF (arrow)
tion should be correctly identied preoperatively.
The C1/2 lateral puncture procedure is also dan-
the spinal canal may compress the spinal cord
(Fig.10.7).
gerous in this variation. Compression myelopathy may result when the variation is bilateral
(Fig.10.6) [5].
10.3 VA Fenestration
andArterialRing
10.2.2 C3 Segmental Type VA
10.3.1 Extracranial
andCraniovertebral Junction
Extremely rarely, the VA enters the spinal canal
via the intervertebral foramen of the C2/3 level
(Figs.10.7 and 10.8). This is referred to as a C3
segmental type VA (Fig. 10.9) [8]. In patients
with a C3 segmental type VA, the unique VA in
Fenestrations can be seen at all 4 segments of the
VA.The V1 segment extends from the origin of
the artery to the entrance into the transverse fora-
VA Fenestration
10.3 VA Fenestration andArterialRing
133
ad
C4
e
C3
b c
C6
C5
Fig. 10.2 (a) P-A projection of CT angiography shows
the left VA arising from the AA proximal to the left SA
(long arrow). The right VA arises from the extreme proxi-
mal right SA (short arrow). (b–e) CT angiographic source
men (Fig. 10.10). The V2 segment runs in the
transverse foramen from the entry level to the C2
(Fig. 10.11). The V3 segment extends from the
C2 to the foramen magnum (Fig.10.12). The V4
segment takes an intradural course to connect to
the basilar artery.
At the craniovertebral junction, from distal V3
to proximal V4, a large fenestration can be seen
relatively frequently (Fig.10.13). Its prevalence
on MR angiography was reported to be 0.9% [7].
As mentioned above (Sect. 10.2.1), the rst intersegmental artery persists normally. When both
the rst and the second intersegmental arteries
images at the levels of C6-C3 show the left VA entering
the C5 TF (long arrow) and the right VA entering the C3
TF (short arrow)
persist, a large fenestration (arterial ring) of the
VA forms at the craniovertebral junction
(Fig.10.14) [6].
10.3.2 Intracranial VA Fenestration
andVBJ Arterial Ring
Fenestrations are relatively frequently seen at the
V4 segment of the VA. The prevalence on MR
angiography was reported to be 0.54% [9].
Fenestration of this segment is usually large, with
the PICA frequently arising from this site
134
IA
BA
C1
C2
C3
Fig. 10.3 Schematic illustration of a C2 segmental type
VA. (Modied from [6]) Normally, the rst intersegmental artery persists. When the rst intersegmental artery
regresses and the second intersegmental artery persists, a
C2 segmental type VA is formed. AICA anterior inferior
cerebellar artery, BA basilar artery, IA intersegmental
artery, PICA posterior inferior cerebellar artery, VA vertebral artery
10 Variations oftheVertebral Artery (VA) andVertebrobasilar Junction (VBJ)
AICA
PICA
1stIA
nd
2
VA
(Fig.10.15) [10]. Thus, duplication may be better
than fenestration for the name of this VA variation [11]. At the terminal segment of the VA,
from the origin of the PICA to the VBJ, a small
fenestration rarely can be seen (Fig. 10.16).
Rarely, a triangular-shaped arterial ring is seen at
the VBJ (Fig.10.17). This is not true fenestration,
rather it is premedullary duplication [11], and its
prevalence on MR angiography was reported to
be 0.18% [9]. The prevalence of V4 segment fenestration in patients with arteriovenous malformation was reported to be high [12].
a b
Fig. 10.4 (a) P-A projection of CT angiography shows
the short V3 segment of the left VA (arrow). (b) Lateral
projection of CT angiography with a bony structure shows
the left VA entering the spinal canal via the C1/2 intervertebral space (arrow)
10.4 VA Termination at thePosterior Inferior Cerebellar Artery (PICA)
abc
135
d
Fig. 10.5 (a) A-P projection of MR angiography and (b)
partial MIP lateral image show short V3 segments of the
bilateral VAs (long arrows). A small fenestration of the
basilar artery (Sect. 11.1) is also seen (dotted arrow). (c,
10.4 VA Termination at
thePosterior Inferior
Cerebellar Artery (PICA)
The terminal segment of the hypoplastic VA is
frequently absent on MR angiography, resulting
in the termination of the VA at the PICA
d) Coronal reformatted source images show bilateral VAs
entering the spinal canal via the C1/2 intervertebral space
(short arrows)
(Fig. 10.18) [13]. There are two possibilities:
congenital aplasia and acquired occlusion.
Basiparallel anatomic scanning (BPAS) is useful
for differentiating between these two conditions
[14]. Using this technique, the occluded arterial
segment can be visualized.
136
10 Variations oftheVertebral Artery (VA) andVertebrobasilar Junction (VBJ)
a
b
d
c
Fig. 10.6 (a) A-P projection of MR angiography shows
the short length of the V3 segments of the bilateral VAs
and a short distance between the VAs at the proximal V4
segments (long and short arrows). (b) MR angiographic
source image at the level of C1 shows bilateral VAs compressing the spinal cord anteriorly (long and short
arrows). (c) P-A projection of CT angiography with a
bone image shows the bilateral VAs entering the spinal
canal at the level of the C1/2 intervertebral space (long
and short arrows). (d) T2-weighted sagittal MR imaging
shows the left VA compressing the spinal cord anteriorly
at the C1 level (long arrow). (Courtesy of Dr. Maki
Umino)
10.4 VA Termination at thePosterior Inferior Cerebellar Artery (PICA)
abc
137
C1/2
d
C2/3
Fig. 10.7 (a) A-P and (b) lateral projections of MR angi-
ography, (c, d) MR angiographic source images show a
hyperplastic left VA entering the spinal canal via the C2/3
intervertebral space, indicative of a C3 segmental type VA
(long arrows). The left VA in the spinal canal is compress-
ing the spinal cord. The hypoplastic right VA enters the
spinal canal via the C1/2 intervertebral foramen, indicative of a C2 segmental type VA (short arrows)
abc
C2
d
C2/3
Fig. 10.8 (a) A-P projection of MR angiography, (b) par-
tial MIP lateral image, and (c, d) MR angiographic source
images show the right VA entering the spinal canal via the
C2/3 intervertebral foramen (arrows), indicative of a C3
segmental type VA
138
IA
Fig. 10.9 Schematic
illustration of a C3
segmental type VA.
(Modied from [8]).
Normally, the rst
intersegmental artery
persists. When the rst
intersegmental artery
regresses and the third
intersegmental artery
persists, a C3 segmental
type VA is formed. AICA
anterior inferior
cerebellar artery, BA
basilar artery, IA
intersegmental artery,
PICA posterior inferior
cerebellar artery, VA
vertebral artery
10 Variations oftheVertebral Artery (VA) andVertebrobasilar Junction (VBJ)
BA
AICA
PICA
1stIA
C1
nd
IA
C2
2
rd
3
C3
VA
a
Fig. 10.10 (a) LAO and (b) P-A projections of CT angi-
ography show the left VA arising from the AA proximal to
the left SA.This artery is divided soon and fuses together,
forming a large slit-like fenestration (arrows). (c) CT
b
c
C6
angiographic source image at the level of C6 shows that
the smaller channel (short arrow) is in the TF, while the
larger channel (long arrow) is located anteriorly
ab
ab
10.4 VA Termination at thePosterior Inferior Cerebellar Artery (PICA)
139
Fig. 10.11 (a) A-P projection of MR angiography and (b) partial MIP image show a small slit-like fenestration at the
V2 segment of the right VA (arrows)
Fig. 10.12 (a) Slightly LAO projection of MR angiography and (b) partial MIP image show a small slit-like fenestra-
tion at the V3 segment of the left VA (arrows)
140
ab
IA
Fig. 10.13 (a) A-P projection of MR angiography and (b) partial MIP image show bilateral large VA fenestrations
(arterial rings) at the C1 level (arrows)
10 Variations oftheVertebral Artery (VA) andVertebrobasilar Junction (VBJ)
Fig. 10.14 Schematic
illustration of bilateral
fenestrations of the VA
at the craniovertebral
junction. (Modied from
[6]). When both the rst
and the second
intersegmental arteries
persist, a large
fenestration (arterial
ring) of the VA at the
craniovertebral junction
is formed. AICA anterior
inferior cerebellar artery,
BA basilar artery, IA
intersegmental artery,
PICA posterior inferior
cerebellar artery, VA
vertebral artery
C1
C2
BA
AICA
PICA
st
1
nd
2
C3
VA
IA