Sylvian Veins, Medycyna, Neurochirurgia - podręczniki
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Neurol Med Chir (Tokyo) 43, 427
¿
434, 2003
Operative Anatomy and Classification of the Sylvian Veins
for the Distal Transsylvian Approach
Ken K
AZUMATA
,HiroyasuK
AMIYAMA
,TatsuyaI
SHIKAWA
,KatsumiT
AKIZAWA
,
Takahiro M
AEDA
,KennichiM
AKINO
,andSatoshiG
OTOH
Department of Neurosurgery, Asahikawa Red Cross Hospital, Asahikawa, Hokkaido
Abstract
Methods for preservation of the sylvian veins in the transsylvian approach have not been established
because of the considerable variations. This study attempted to classify the sylvian veins to facili-
tate systematic dissection of the sylvian fissure for sylvian veins to be preserved. The operative
anatomy of the sylvian vein was examined in 82 hemispheres. The type of drainage and the pattern of
branching were investigated. The superficial sylvian vein (SSV) was classified into three types ac-
cording to the number of stems draining into the dural sinus on the inner surface of the sphenoid
bone: The SSV was absent or hypoplastic in eight cases, the SSV was single in 38 cases, and the SSV
was double in 36 cases. The SSV drained into neither the sphenoparietal sinus nor the cavernous
sinus in nine cases. An anastomosis between the SSV and the deep middle cerebral vein (DMCV) was
observed in 42 cases. The frontobasal bridging vein (FBBV) drained into the sphenoparietal sinus in
47 cases. The type of connection was further subdivided into four types according to the connections
with the DMCV and FBBV. The venous anatomy of sylvian fissure indicates that dissection (skeleton-
ization) of the main stem of sylvian veins from the temporal lobe should be performed to preserve the
tributaries from the frontal lobe.
Key words: transsylvian approach, sylvian vein, sylvian fissure
Introduction
frequent variations in the sylvian veins.
This study investigated the anatomical variations
of the sylvian veins in the sylvian fissure in 82 sides
in 82 patients undergoing surgical exploration who
required the transsylvian approach because of
pathology such as cerebral aneurysm or parasellar
tumor. Based on the pattern followed by these
variations, an optimum method of the dissection is
proposed, which allows adequate working space
without sacrificing of the sylvian veins.
The sylvian veins show frequent variations in size
and connection.
1,2,4,6,8,9)
Previous studies of the
sylvian veins have focused on the outflow point,
using angiography, three-dimensional computed
tomography (CT), or cadaver study.
3,10–13)
The gold
standard for surgery in this area suggests that ``the
arachnoid of the sylvian fissure should be opened on
the frontal side of the veins, so that they will not
cross the sylvian fissure when the frontal lobe is
retracted. Occasionally two or three fronto-orbital
venous tributaries that cross the sylvian fissure to
enter the middle cerebral vein need to be sacrificed
to complete the dissection.''
17)
However, the
sacrifice of the sylvian veins could result in
postoperative venous infarction or contusion of
the frontal lobe.
7,10)
We have employed the distal
transsylvian approach to preserve the sylvian veins
and tributaries.
6)
However, a systematic stepwise
method of microsurgical dissection to preserve the
sylvian veins is difficult to describe because of the
Patients and Methods
Eighty-two patients with internal carotid artery
(ICA) or distal basilar artery aneurysm, or parachias-
matic neoplasm necessitating the transsylvian
approach or a modification such as the anterior
temporal approach were treated at the Neurosurgi-
cal Department of Asahikawa Red Cross Hospital
between 1998 and 2001.
Microsurgical dissection of 82 sides was per-
formed through the distal transsylvian approach as
described in detail elsewhere.
6)
Briefly, dissection
was started about 1–2 cm distal to the lateral
Received March 1, 2002; Accepted April 17, 2003
427
427
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K. Kazumata et al.
Fig. 1 Diagram illustrating typical branching of
the sylvian vein consisting of the temporo-
superior sylvian vein (tSSV), and the fronto-
superior sylvian vein (fSSV) with the deep
middle cerebral vein (DMCV) and the fron-
tobasal bridging vein (FBBV). Superficial
part: the number, location, and outflow
point are highly variable for the veins of the
lateral fronto-orbital gyrus. Intermediate
part: the DMCV courses behind the
posterior division of the middle cerebral ar-
tery. Basal part: FBBV consists of tributar-
ies of the olfactory vein, anterior cerebral
vein, and posterior orbitofrontal vein. The
common vertical trunk is the proximal seg-
ment of the fSSV, to which the DMCV and
FBBV can join. Note that the major tribu-
tariesofsylvianveinprimarilydraininto
the fSSV.
patterns (Fig. 1). Veins in the sylvian fissure can be
categorized into the superficial, intermediate, and
basal parts.
Superficial part: The superficial part consists of
the superficial sylvian vein (SSV) (superficial middle
cerebral vein). Usually, the SSV consists of the
fronto-orbital (fronto-SSV: fSSV), fronto-parietal
(parieto-SSV), and anterior temporal (temporo-SSV:
tSSV) veins.
1,2)
We defined single SSV as an SSV
with tributaries from both the frontal and temporal
lobesthatdrainsintotheduralsinusasasingle
trunk. Double SSVs at the entrance of the dural sinus
consist of one SSV with tributaries from the frontal
lobe (fSSV), and another SSV with tributaries from
thetemporallobe(tSSV).Thereisalsoasmallveinat
the anterior temporal region, which has tributaries
from the middle and inferior temporal gyri, and may
be called the temporopolar vein. However, this study
did not analyze the temporopolar vein.
Intermediate part: The intermediate part consists
of insular veins. A previous study found the insular
veins consist of four veins of the anterior limiting
sulcus, precentral sulcus, central sulcus, and pos-
terior limiting sulcus.
12,16)
Drainage of the common
stem of the insular vein can be classified into two
types: the classic pattern with a common stem
draining into the basal vein, and the nonclassic
pattern with a common stem draining into the
sphenoparietal sinus (SPS).
12)
This study assessed
the anastomosis between the common stem of the
insular veins and the SSV. Absence of an anastomo-
sis in the operative field indicated the common stem
of the insular veins primarily drained into the basal
vein. In this type, the intermediate part has no
influence on sylvian dissection.
Basal part: The basal part consists of the olfactory
vein, posterior fronto-orbital vein, anterior cerebral
vein, and twigs from the optic chiasm. All these
veins are components of the first part of the basal
vein.
10)
If these veins drain into the basal vein, there
is no vein that passes over the ICA. In this study, a
small vein running from the frontal base and drain-
ing into the SPS was called a frontobasal bridging
vein (FBBV). An FBBV can drain into the SPS as a
single trunk, or as a common stem with the SSV or
an anastomotic vein with the common stem of the
insular veins (common vertical trunk).
15)
orbitofrontal gyrus. The anterior trunk of middle
cerebral artery (MCA) on the insular surface was
identified, then the dissection proceeded to follow
the M
1
segment and ICA in a retrograde fashion. The
last step of dissection was incision of the arachnoid
trabecula wall over the carotid cistern. The drainage
route and pattern of branching of the sylvian veins
were recorded during the operation and also on
videotapes.
II. Drainage pattern
SSV
: The drainage and multiplicity of the SSV
was classified into three types: Type I, the SSV was
absent or very hypoplastic (8 cases, 10%); Type II,
the SSV consisted of a single main stem draining
into the SPS (38 cases, 46%); and Type III, the SSV
consisted of two main stems (fSSV and tSSV) drain-
Results
I. Nomenclature
The variations of sylvian veins were classified
according to the branching and drainage pathway
Neurol Med Chir (Tokyo) 43, September, 2003
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Anatomy of Sylvian Vein
429
Fig. 2 Diagrams showing the patterns of branch-
ing of Type II. A: superficial sylvian vein
(SSV) only, B: SSV
+
frontobasal bridging
vein(FBBV),C:SSV
+
deep middle cerebral
vein(DMCV),D:SSV
+
DMCV
+
FBBV.
Fig. 3 Diagrams showing the patterns of branch-
ing of Type III. A: temporo-superficial syl-
vian vein (tSSV)
+
fronto-superficial sylvi-
an vein (fSSV), B: tSSV
+
(fSSV
+
fron-
tobasal bridging vein [FBBV]), C: tSSV
+
(fSSV
+
deep middle cerebral vein
[DMCV]), D: tSSV
+
(fSSV
+
DMCV
+
FBBV).
ing into the SPS (36 cases, 44%).
Insular veins:Theinsularveinsformedan
anastomotic stem trunk and drained into the SPS in
42 cases (51%). There was no anastomosis between
the insular veins and the SPS in 40 cases (49%).
FBBV: An FBBV was found in 47 cases. The olfac-
tory vein, posterior fronto-orbital vein, anterior
cerebral vein, and twigs from the optic chiasm were
considered to form the first part of the basal vein in
35 cases.
10)
theSPS(7cases);TypeIIIb,theDMCVdrainedinto
the fSSV and the fSSV and tSSV drained into the SPS
(8 cases); Type IIIc, the FBBV drained into the fSSV
and the fSSV and tSSV drained into the SPS (10
cases); and Type IIId, both the FBBV and DMCV
drained into the fSSV and the fSSV and tSSV
drained into the SPS (9 cases). The pattern of
branching did not fall into this classification in two
cases of Type III.
III. Type of branching
The patterns of branching could be further classi-
fied. Type II showed four subtypes (Fig. 2): Type IIa,
only the SSV, but not the deep middle cerebral vein
(DMCV) and FBBV, drained into the SPS (3 cases);
Type IIb, the FBBV drained into the SSV and the
SSV drained into the SPS (8 cases); Type IIc, the
DMCV drained into the SSV and the SSV drained
into the SPS (10 cases); and Type IId, both the FBBV
and DMCV drained into the SSV and the SSV
drained into the SPS (10 cases). The pattern of
branching did not fall into this classification in
seven cases of Type II.
Type III showed four subtypes similar to those of
Type II plus a tSSV (Fig. 3): Type IIIa, only the tSSV
+
fSSV, but not the DMCV and FBBV, drained into
Discussion
I. Operative anatomy of the sylvian vein
The present study revealed that the SSV was
present in 90% of cases. Previous studies of the
drainage pathway of the SSV found that the SSV
drains into the SPS in 68.2%, cavernous sinus
directly in 21%, middle meningeal vein in 10%,
superior petrosal sinus in 0.71%, and emissary vein
in the foramen lacerum in 0.71%.
3)
The drainage
route can be assessed preoperatively by angiography
or three-dimensional CT angiography.
11–13,15)
In our
study, the entrance of the SSV was recognized at the
pretemporal dura matter in the operative field in
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K. Kazumata et al.
Fig. 4 A: Diagram showing a coronal section of the distal part of the sylvian fissure. The double
layer of the arachnoid membrane envelops superficial sylvian vein (SSV) circumferentially.
The arachnoid trabecula wall spreads over the insular surface and M
2
segment of middle
cerebral artery (MCA). The anterior division of the MCA is usually recognized at the initial
stage of dissection. The posterior division of the MCA is located more laterally, and the deep
middle cerebral vein (DMCV) is located underneath. fSSV: fronto-SSV, tSSV: temporo-SSV.
B: Diagram showing the importance of microsurgical dissection between the fSSV and tSSV.
The vein of the lateral fronto-orbital gyrus will not cross the sylvian fissure. The lateral
fronto-orbital gyrus often herniates into the temporal operculum, so the dissection is easier to
perform in the distal to proximal direction (arrow).
Fig. 5 Diagrams showing the dissection of the sylvian veins in Type II. A: Incorrect dissection
between the frontal lobe and superficial sylvian vein (SSV) (arrow).Theworkingspaceis
limited by the length of A, unless the vein of the lateral fronto-orbital gyrus is sacrificed. B:
Correct dissection should be performed between the SSV and superior temporal gyrus
(arrows). The working space is increased to the length of A plus B. C: Completed dissection.
Small tributaries from the superior temporal gyrus can be mobilized in most cases (arrows).
DMCV: deep middle cerebral vein, ICA: internal carotid artery, ON: optic nerve.
90% of cases. This finding is consistent with the
previous findings that the SSV drains either into the
SPS or directly into the cavernous sinus in 62–89%
of cases.
3,11)
Thevenousdrainageofinsulaisprimarilyviathe
DMCV. The drainage of the common stem of the
insular vein can be classified into two types: the
classic pattern with a common stem draining into
the basal vein, and the nonclassic pattern with a
common stem draining into the SPS as a common
vertical trunk.
15)
The venous configuration of the
insula reflects a mixture of superficial and deep
Neurol Med Chir (Tokyo) 43, September, 2003
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Anatomy of Sylvian Vein
431
Fig. 6 Diagram showing the dissection of the sylvian veins in Type III. A:
Arrows
indicate the site
of dissection that is necessary to obtain the maximum working space. The deep middle
cerebral vein (DMCV) courses behind the posterior division of the middle cerebral artery,
then drains into the fronto-superficial sylvian vein (fSSV) or vein of the lateral fronto-orbital
gyrus. The proximal part of the DMCV is dissected from the frontal and temporal lobes. The
sylvian vein complex consists of the fSSV (common vertical trunk) which can be mobilized
toward the frontal side. FBBV: frontobasal bridging vein, tSSV: temporo-superficial sylvian
vein. B: The veins of the lateral orbitofrontal gyrus frequently join with the DMCV, and
drain into the fSSV. If the proximal segment of the anterior temporal artery (arrow) courses
like a loop in the planum polare, the common vertical trunk is anchored on the anterior
temporal artery (circle).
Fig. 7 Diagrams showing dissection of the sylvian veins in the sphenobasal or sphenopetrosal vein
type. A: Dissection for the sphenobasal and sphenopetrosal vein types. Arrows indicate the
proximal part of the sylvian vein. SSV: superficial sylvian vein. B: The method of dissection
is similar to those used in Types II and III. FBBV: frontobasal bridging vein.
connections.
14)
We found a significant anastomosis
between the SSV and the common trunk of insular
veins in 51% of cases. This anastomotic trunk has
been called a common vertical trunk, with which the
tributaries from the frontal base (FBBVs) can also
join.
15)
In the majority of cases, the anastomosis of
the common stem of the insular veins and the SSV
occurs between the fSSV and the common stem of
Neurol Med Chir (Tokyo) 43, September, 2003
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