Sylvian Veins.pdf

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

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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

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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

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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

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