Venous Anatomy of the Sphenoparietal Sinus: Evaluation by MR Imaging

Abstract

The termination of the superficial middle cerebral vein (SMCV) has been described as entering or being partially equivalent to the venous sinus coursing under the lesser sphenoid wing, which has classically been called the sphenoparietal sinus. However, the recent literature reports that the SMCV is not connected to the sphenoparietal sinus. In this study, the venous anatomy was evaluated to clarify the anatomy of the sphenoparietal sinus and the termination of the SMCV. Magnetic resonance imaging (MRI) was performed on 1.5-T superconductive units using a three-dimensional fast spoiled gradient-recalled acquisition in the steady state (3-D fast SPGR) sequence with fat suppression in a total of 48 sides of 24 patients. Coronal source images and reconstructed axial images were displayed on the Advantage Window Console, and connections to the cavernous sinus were then evaluated for the venous sinus coursing under the lesser sphenoid wing (hereafter called the sinus of the lesser sphenoid wing), the middle meningeal vein, and the SMCV.
The following findings were observed bilaterally in all patients. The sinus of the lesser sphenoid wing was connected medially with the cavernous sinus and laterally with the anterior branch of the middle meningeal vein near the pterion.
The anterior branch of the middle meningeal vein entered the bony canal laterally above the junction with the sinus of the lesser sphenoid wing and coursed along the inner table of the skull or emerged into the diploic vein, indicating its parietal portion. Although the termination of the SMCV had several patterns, the SMCV was not connected with the sinus of the lesser sphenoid wing in any of the patients. The sphenoparietal sinus is considered to consist of the sinus of the lesser sphenoid wing and the parietal portion of the anterior branch of the middle meningeal vein; these were identified as venous structures distinct to the SMCV.

Full text

Venous Anatomy of the Sphenoparietal Sinus: Evaluation by MR Imaging S. Takahashi
84
The anterior branch of the middle meningeal
vein entered the bony canal laterally above the
junction with the sinus of the lesser sphenoid
wing and coursed along the inner table of the
skull or emerged into the diploic vein, indicating
its parietal portion. Although the termination of
the SMCV had several patterns, the SMCV was
not connected with the sinus of the lesser sphe-
noid wing in any of the patients. The
sphenoparietal sinus is considered to consist of
the sinus of the lesser sphenoid wing and the
parietal portion of the anterior branch of the
middle meningeal vein; these were identified as
venous structures distinct to the SMCV.
Introduction
The termination of the superficial middle
cerebral vein (SMCV) is important in transve-
nous embolization of cavernous sinus dural ar-
teriovenous fistula (AVF). This is because coil
packing must be started at the junction of the
cavernous sinus and the SMCV to prevent cor-
tical venous reflux that could cause venous
congestion of the brain parenchyma. However,
the termination of the SMCV reveals several
patterns and some authors have reported that
this vein can join the sphenoparietal sinus 1-4.
In such cases, it would be important to iden-
tify the sphenoparietal sinus in order to per-
form treatment. The sphenoparietal sinus is
Summary
The termination of the superficial middle
cerebral vein (SMCV) has been described as en-
tering or being partially equivalent to the venous
sinus coursing under the lesser sphenoid wing,
which has classically been called the spheno-
parietal sinus. However, the recent literature re-
ports that the SMCV is not connected to the
sphenoparietal sinus. In this study, the venous
anatomy was evaluated to clarify the anatomy of
the sphenoparietal sinus and the termination of
the SMCV. Magnetic resonance imaging (MRI)
was performed on 1.5-T superconductive units
using a three-dimensional fast spoiled gradient-
recalled acquisition in the steady state (3-D fast
SPGR) sequence with fat suppression in a total
of 48 sides of 24 patients. Coronal source images
and reconstructed axial images were displayed
on the Advantage Window Console, and connec-
tions to the cavernous sinus were then evaluated
for the venous sinus coursing under the lesser
sphenoid wing (hereafter called the sinus of the
lesser sphenoid wing), the middle meningeal
vein, and the SMCV.
The following findings were observed bilater-
ally in all patients. The sinus of the lesser sphe-
noid wing was connected medially with the cav-
ernous sinus and laterally with the anterior
branch of the middle meningeal vein near the
pterion.
Venous Anatomy
of the Sphenoparietal Sinus:
Evaluation by MR Imaging
S.TAKAHASHI, I. SAKUMA, T. OTANI, K. YASUDA, N. TOMURA, J. WATARAI,
T. YANAGISAWA*, K. MIZOI*
Departments of Radiology and Neurosurgery*, Akita University School of Medicine
Key words: sphenoparietal sinus, superficial middle cerebral vein, MRI

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85
classically defined as the venous sinus under
the lesser sphenoid wing 1. The purpose of this
study was to clarify the venous anatomy of the
sphenoparietal sinus and the termination of the
SMCV in order to facilitate the transvenous
embolization of cavernous sinus dural AVF.
Methods
Subjects were 24 patients (ten males and 14
females; age range, 20-75 years; mean age, 54.3
years); both sides were examined in each pa-
tient (i.e. a total of 48 sides). Conditions includ-
Figure 1 A 40-year-old woman with arteriovenous malformation of the left basal ganglia.The coronal source images (A-D) of
the middle cranial fossa was obtained by contrast-enhanced 3-D fast SPGR. The sinus of the lesser sphenoid wing (SLSW) is
identified to be connected medially with the cavernous sinus and laterally with the anterior branch of the middle meningeal
vein near the pterion. The SMCV courses near the SLSW and enters the cavernous sinus independently of the SLSW.
CS, cavernous sinus; diploic v, diploic vein; MCA, middle cerebral artery; MMV, anterior branch of the middle meningeal
vein; MMV parietal, parietal portion of the anterior branch of the middle meningeal vein; SLSW, sinus of the lesser sphenoid
wing; SMCV, superficial middle cerebral vein.
A B
DC

Venous Anatomy of the Sphenoparietal Sinus: Evaluation by MR Imaging S. Takahashi
86
ed brain tumor (n=17) cerebral arteriovenous
malformation (n=2), multiple sclerosis (n=1),
dural AVF of the transverse sinus (n=1), eth-
moid sinus tumor (n=1), old brain contusion
(n=1), and hearing disturbance (n=1). After in-
travenous Gd-DTPA injection, magnetic reso-
nance imaging (MRI) was performed on 1.5-T
superconductive units using a three-dimension-
al fast spoiled gradient-recalled acquisition in
the steady state (3-D fast SPGR) sequence
with fat suppression. The center of the volume
slab was located on the anterior clinoid process
in the sagittal localizer image, and coronal im-
ages were acquired with the following parame-
ters: repetition time/echo time/excitations, 21-
26/2-3/1; 18-cm field of view, 1.0 or 1.5 mm slice
thickness, 60 slices, flip angle 15°, and 256 x 256
matrix. Coronal source images and reconstruct-
ed axial images were displayed on the Advan-
tage Window Console within a few minutes,
Figure 2 Schema of the SMCV and sphenoparietal sinus (axial view).The termination of the SMCV can be classified into the
following four basic types; cavernous sinus type (Cav), paracavernous sinus type (Para), laterocavernous sinus type (Latero),
and absent type (not shown). The SMCV enters the anterolateral aspect of the cavernous sinus in the cavernous sinus type.The
SMCV courses outside the cavernous sinus and enters the foramen ovale or the superior petrosal sinus in the paracavernous
sinus type.The SMCV enters the lateral wall of the cavernous sinus, coursing between the two layers in the laterocavernous si-
nus type.The sinus of the lesser sphenoid wing (SLSW) enters the anterolateral aspect of the cavernous sinus medially and con-
nects with the anterior branch of the middle meningeal vein (MMV) laterally and continues to the parietal portion of anterior
branch of the middle meningeal vein (Parietal MMV). The sphenoparietal sinus consists of the sinus of the lesser sphenoid
wing and the parietal portion of the middle meningeal vein, and enters the cavernous sinus independently of the SMCV.
Cav, cavernous sinus type; Latero, laterocavernous sinus type; Para, paracavernous sinus type;CS, cavernous sinus;MMV, an-
terior branch of the middle meningeal vein; Parietal MMV, parietal portion of the anterior branch of the middle meningeal
vein; SLSW, sinus of the lesser sphenoid wing; SMCV, superficial middle cerebral vein; SOV, superior ophthalmic vein.

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and connections to the cavernous sinus were
then evaluated for the venous sinus under the
lesser sphenoid wing, the middle meningeal
vein, and the SMCV.
Results
The major vessels were identified around the
cavernous sinus and in the middle cranial fossa,
and the following findings were observed bilat-
erally in all patients (figure 1). The venous si-
nus coursing under the lesser sphenoid wing
was identified to be connected with the cav-
ernous sinus medially. This venous sinus (there-
after called the sinus of the lesser sphenoid
wing) was connected near the pterion with the
anterior branch of the middle meningeal vein
that coursed from the foramen spinosum along
the vascular groove in the floor of the middle
cranial fossa.
The anterior branch of the middle meningeal
vein entered the bony canal laterally above the
junction with the sinus of the lesser sphenoid
wing and coursed along the inner table of the
skull or emerged into the diploic vein. It was
difficult to identify the anterior branch of the
middle meningeal artery that anatomically
ought to course along the anterior branch of
the middle meningeal vein.
The termination of the SMCV was classified
into the following four types (figure 2). In type
1 (cavernous sinus type), the SMCV entered
the anterolateral aspect of the cavernous sinus;
this was observed in 17 sides of 14 patients
(35.4%). In type 2 (paracavernous sinus type),
the SMCV coursed outside the cavernous sinus
and entered the foramen ovale or the superior
petrosal sinus; this was found in five sides of
four patients (10.4%).
In type 3 (laterocavernous sinus type), the
SMCV entered the lateral wall of the cav-
ernous sinus; this occurred in eight sides of sev-
en patients (16.7%). In this type, because the
SMCV courses between the two layers of the
lateral wall of the cavernous sinus and enters
the pterygoid plexus, the diameter of the SM-
CV decreases within the lateral wall. Although
the two layers of the lateral wall of the cav-
ernous sinus could not be identified, the nar-
row SMCV diameter in the lateral edge of the
cavernous sinus indicated this type. Finally, in
type 4, the SMCV was absent; this was identi-
fied in 17 sides of 11 patients (35.4%). It was
difficult to determine the laterocavernous sinus
type or the cavernous sinus type in one side of
one patient (2.0%). The SMCV was not con-
nected with the sinus of the lesser sphenoid
wing or the middle meningeal vein in any of
the patients.
Discussion
The literature contains various anatomic de-
scriptions of the sphenoparietal sinus and ter-
mination of the SMCV 1-7. Wolf et Al 1described
the SMCV entering the dura in the region of
the pterion and running along the lesser wing
of the sphenoid to enter the anterior end of the
cavernous sinus.They mentioned that the dural
portion of this channel along the lesser sphe-
noid wing had been frequently referred to as
the sphenoparietal sinus, and they suggested
that the term “sinus of the lesser wing of the
sphenoid” should be preferred. Oka et Al2re-
ported that the SMCV could either join the
sphenoparietal sinus or drain directly into the
cavernous sinus. In a study of 140 cadaveric
heads, Bisaria 3reported that the SMCV termi-
nated into the sphenoparietal sinus in 67.1%.
Similarly, in an MRI study of 100 patients using
3-D contrast-enhanced magnetization-pre-
pared rapid gradient-echo (MP-RAGE), Iku-
shima et Al4reported that the SMCV entered
the sphenoparietal sinus in 57.5%. However, in
a study of 15 nonfixed human specimens using
the corrosion cast technique, San Millan Ruiz
et Al 5recently clarified that SMCV was not
connected to the sphenoparietal sinus in any of
the specimens. They reported that the sphe-
noparietal sinus consists of the artificial combi-
nation of two venous structures, the parietal
portion of the anterior branch of the middle
meningeal vein and a sinus of the lesser sphe-
noid wing. They found that the SMCV drained
into the paracavernous sinus, laterocavernous
sinus, and the cavernous sinus 5-7, and they pro-
posed that the classic notion of the SMCV
draining into or being partially equivalent to
the sphenoparietal sinus had been erroneous 5.
In the present study, the SMCV was not
found to enter the sphenoparietal sinus, sup-
porting the findings of San Millan Ruiz et Al5.
Although the termination of the SMCV was
very close to the sinus of the lesser sphenoid
wing in some cases, these two venous structures
could be distinguished from each other on
MRI. The anterior branch of the middle
meningeal vein entered the bony canal lateral-

Venous Anatomy of the Sphenoparietal Sinus: Evaluation by MR Imaging S. Takahashi
88
Figure 3 A 62-year-old man with dural AVF of the left cavernous sinus. Right external carotid arteriograms in frontal (A)
and lateral (B) projections show dural AVF of the left cavernous sinus (white arrow). The dural AVF drains into the left in-
ferior petrosal sinus (double black arrows). Note the cortical venous reflux into the left SMCV (black arrow).Venograms of
the left sinus of the lesser sphenoid wing (C) and the left SMCV (D) were performed gently by manual injection in a frontal
projection via the left inferior petrosal sinus. The lateral portion of the sinus of the lesser sphenoid wing is obscure because
of the remaining contrast media (C). The SMCV and the sinus of the lesser sphenoid wing connect with the cavernous sinus
independently. Right external carotid arteriogram in a frontal projection (E) immediately after transvenous coil emboliza-
tion of the left cavernous sinus shows disappearance of dural AVF.The venous phase of the left internal carotid arteriogram
in a lateral projection (F) shows the left SMCV (black arrow), demonstrating improved venous circulation.
A B
D
F
C
E

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ly above the junction with the sinus of the less-
er sphenoid wing and coursed along the inner
table of the skull or emerged into the diploic
vein. These findings were also compatible with
those of San Millan Ruiz et Al5. The spheno-
parietal sinus is considered to consist of the si-
nus of the lesser sphenoid wing and the parietal
portion of the anterior branch of the middle
meningeal vein (figure 2).
In transvenous coil embolization of cav-
ernous dural AVF, it is important to identify the
junction of the SMCV with the cavernous sinus
in order to prevent cortical venous reflux into
the SMCV (figure 3). According to the results
of our study, embolization of the junction be-
tween the sphenoparietal sinus and the cav-
ernous sinus would not be of use because the
SMCV does not enter the sphenoparietal sinus.
It is therefore important to assess the SMCV
termination by precise evaluation of the ve-
nous phase of cerebral arteriography before
treatment. MRI using contrast-enhanced 3-D
fast SPGR sequence with fat suppression is al-
so useful for evaluation of the SMCV termina-
tion. Although evaluation of the SMCV termi-
nation was difficult due to anteroposterior
shortening of the volume slab when the SMCV
turned posteriorly, we selected coronal orienta-
tion rather than axial orientation in order to
overcome this problem.
In this study, it was necessary to observe on-
ly the relationship among the sinus of lesser
sphenoid wing, the middle meningeal vein, the
SMCV, and the cavernous sinus. It takes longer
to obtain information from the floor of the
middle cranial fossa to the parietal calvarium in
the axial orientation than in the coronal orien-
tation. The information obtained by our
method was sufficient to evaluate the venous
structures around the cavernous sinus de-
scribed above.
Conclusions
The sphenoparietal sinus consists of the sinus
of the lesser sphenoid wing and the parietal
portion of the anterior branch of the middle
meningeal vein. The SMCV was not found to
enter the sphenoparietal sinus; the sphenopari-
etal sinus and SMCV appear to be independent
of each other. MRI using contrast-enhanced 3-
D fast SPGR sequence with fat suppression is
useful for evaluation of these venous struc-
tures.
Satoshi Takahashi, M.D.
Akita University School of Medicine
Department of Radiology
1-1-1 Hondo
Akita 010-8543, Japan
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