Sylvian Cistern.pdf

SAGITTAL ANATOMY OF THE SYLVIAN CISTERN

Anil A Kilpadikar M.D.*, Edgardo J Angtuaco M.D.*,

Rudy L VanHemert M.D.*, Eren Erdem M.D.*, Gazi M Yasargil M.D.**

*Dept. of Radiology, **Dept. of Neurosurgery, University of Arkansas for Medical Sciences, Little Rock Arkansas.

INTRODUCTION:

The Sylvian cistern is well understood and

described in the anatomical and surgical

literature 2,7 . Computed tomography (CT) and

magnetic resonance (MR) have advanced our

knowledge of this area. Description of the

sylvian cistern is generally done in the axial

and coronal planes. The sagittal plane is

underutilized but adds another dimension to

anatomy not observed in the other planes. In

particular, the triangular shaped insular cortex

with its gyri and sulci, is well depicted in this

plane. In this exhibit we present the normal

sagittal MRI anatomy and various examples of

pathology occurring in this area.

The Sylvian issure is divided into anterior (stem) and posterior (insuloopercular)

compartments 5,6 (Fig 3, 4) The limen insulae forms the junction point or knee

between the anterior and posterior stem. 5 (Fig 2, 3, 4). This is the most lateral

limit of the anterior perforated substance and is the starting point of the

triangular shaped insular cortex. Anterior, superior and inferior periinsular sulci

demarcate the limits of the insular cortex and the sulci demarcate the insular

cortex from the adjacent opercula. (Fig 2, 3).

The insula is classiied as part of the paralimbic system and a variety

of functions have been attributed to it including memory, drive, affect,

gustation, and olfaction 1 .

The horizontal or M1 segment of the MCA extends laterally

in the depths of the sylvian issure, from its origin at the

ICA bifurcation to its bifurcation or trifurcation at the knee

dividing into the anterior temporal artery, the superior

trunk and the inferior trunk The insular or M2 segments

(superior trunk, inferior trunk and its branches) begin at

the limen insula (genu) extend to the periinsular sulci and

loop over the insular cortex. The opercular or M3 segments

extend from the periinsular sulci and ramify over the lateral

hemispheric surface in the sylvian issure. 3,6 (Fig 6)

The central insular sulcus, the main and the deepest sulcus of the

insula, courses obliquely across the insula, and extends uninterrupted

from the limen insula to the superior periinsular sulcus. It divides

the insula into two unequal zones: the larger anterior insula, and the

smaller posterior insula . (Fig 2, 3)

The frontoorbital, frontoparietal and temporal opercula enclose the insula. (Fig 1,

2). The operculum encloses areas which are vital to perception and motor aspects

of speech, auditory function and secondary somatic sensory and motor functions. 1

The anterior insula is composed of the triangular and three principal

short insular gyri (anterior, middle and posterior). The anterior, middle

and posterior short insular gyri are separated by the short insular

sulcus and the pre-central insular sulcus. The gyri of the anterior insula

fuse to form the insular apex (Fig 2, 3), which is its most supericial

area. The posterior insula is composed of anterior and posterior long

insular gyri which are separated by the post-central insular sulcus. The

cortical grey matter of the insular cortex is continuous with that of the

different opercula (Fig 2, 3, 4, 5). The extreme capsule, consisting of

the subcortical white matter of the insular cortex is continuous with the

white matter of the opercula. (Fig 4, 5)

Arteries supplying the insular cortex predominantly

originate from the M2 segment of the MCA, with a few

arising from the M3 segment. They also supply the extreme

capsule and occasionally the claustrum and external

capsule. Few branches from the M1 segment supply the

limen insula. 6

Fig 2. Normal Anatomy. A. Sagittal T1-

weighted MR image and corresponding

surgical anatomy specimen through

the insular cortex deining the insular

borders, gyri and sulci. B. Sagittal T1-

weighted image and corresponding

surgical anatomy specimen through

the opercula. alg anterior long insular

gyrus, aps anterior periinsular sulcus,

asf anterior stem of sylvian issure,

asg anterior short insular gyrus, cis

central insular sulcus, foo frontoorbital

operculum, fpo frontoparietal

operculum hg Heschl’s gyrus, ia

insular apex, ips inferior periinsular

sulcus, msg middle short insular gyrus,

pcis postcentral insular sulcus, pis

precentral insular sulcus, plg posterior

long insular gyrus, pps posterior periinsular sulcus, psf posterior stem of Sylvian issure, psg posterior

short insular gyrus, sis short insular sulcus, smg supramarginal gyrus, sps superior periinsular sulcus,

to temporal operculum

ANATOMY:

The Sylvian cistern is the subarachnoid space

extending into the Sylvian issure. It is bounded

by the insular cortex (island of Reil) 4 and the

opercular cortex (frontoorbital, frontoparietal

and temporal). Within the Sylvian cistern lies the

middle cerebral artery (MCA) and its branches.

The opercula (lobes) cover and encase the

insular cortex (Fig 1). The Sylvian issure, insular

cortex and operculum are anatomically intimately

related to each other.

Fig 4.

Normal Axial

Anatomy.

A. Axial T1-

weighted

STIR images

at level of

atem of

sylvian

issure.

B. at level

of inferior

insular cortex. C. at level of superior insular cortex. as anterior perforated substance, asf

anterior stem of Sylvian issure, c caudate nucleus, ec external capsule, gp globus pallidus,

i internal capsule, ic insular cortex, li limen insula, mca middle cerebral artery, p putamen,

psf posterior stem of sylvian issure, t thalamus

Fig 6A. Normal Arterial Anatomy.

Lateral projection of right internal

carotid angiogram and surgical

anatomy specimen showing the

arteries in the insula: 2 prefrontal

artery, 3 precentral artery, 4 central

artery, 5 anterior parietal artery, 6

posterior parietal artery. 7 angular

artery, it inferior trunk, pca posterior

communicating artery, st superior

trunk.

Sylvian issure anatomy is variable and

extends on the lateral surface of the brain

from the anterior perforated substance to the

supramarginal gyrus. It separates the frontal and

parietal lobes from the temporal lobe and the

insular cortex from its loor. 5 (Fig 1, 2,)

Fig 1. Normal

Anatomy. A.

Lateral surface of

the brain showing

the various

issures, sulci and

gyri. B. Separation

of the opercula

reveal the insular

cortex (central

lobe) Printed

from Applied

Anatomy: Davis

GG, Philadelphia:

J.B.Lippincott Co,

1910,pp 32,33.

Fig 5.

Normal

Coronal

Anatomy.

A Coronal

T1-weighted

STIR

image at

the anterior

stem of sylvian issure. B. at level of anterior part of posterior stem of Sylvian issure. C.

at level of posterior part of posterior stem of Sylvian issure. asf anterior stem of Sylvian

issure, c caudate nucleus, cl claustrum, ec external capsule, exc extreme capsule, fpo

frontoparietal operculum, gp globus pallidus, h hippocampus, i internal capsule, ic insular

cortex, p putamen, psf posterior stem of sylvian issure, to temporal operculum, si

substantia innominata

Fig 3. Normal Sagittal Anatomy. A. Sagittal T1-weighted STIR image through insular cortex. B. lateral

to the insular cortex. C. through opercula. ahg anterior Heschl’s gyrus, alg anterior long insular gyrus,

aps anterior periinsular sulcus, asf anterior stem of Sylvian issure, asg anterior short insular gyrus, cis

central insular sulcus, foo frontoorbital operculum, fpo frontoparietal operculum, ia insular apex, ips

inferior periinsular sulcus, msg middle short insular gyrus, pcis postcentral insular sulcus, phg posterior

Heschl’s gyrus, pis precentral insular sulcus, plg posterior long insular gyrus, pps posterior periinsular

sulcus, psf posterior stem of sylvian issure, psg posterior short insular gyrus, sis short insular sulcus,

smg supramarginal gyrus, sps superior periinsular sulcus, tg triangular gyrus, to temporal operculum

Fig 6B. frontal projection of right internal angiogram. 1 internal carotid artery,

2 horizontal (M1) MCA segment, 3 lateral lenticulostriate arteries, 4 MCA

bifurcation, 5 anterior temporal artery, 6 M2 (Sylvian) segments of MCA

hemispheric branches, 7 M3 (opercular) MCA branches, 8 Sylvian point.

INSULAR LESIONS:

OPERCULAR LESIONS:

CONCLUSIONS:

Sagittal imaging although included in routine

protocols in MR studies of the brain, is

underutilized in interpreting lesions around the

Sylvian cistern. While axial and coronal images

demonstrate the insula as a rim of cortex, the

sagittal plane displays the triangular shape of the

insula and depicts the various gyri and sulci which

compose the anatomy of the insular cortex. The

addition of other imaging sequences in the sagittal

plane, such as FLAIR, T1-weighted STIR-FSE or

contrast studies, can be used to better display

lesions around the Sylvian cistern. Neurosurgeons

using the Sylvian issure as a surgical approach

will ind the sagittal plane as a good anatomical

guide for preoperative planning.

9 10

Fig 7 . Insular

Glioma. A. Sagittal

postgadolinium T1-weighted MR image through the right

insular cortex demonstrates an isointense nonenhancing

mass ( Ú ) occupying the insular cortex. B. Sagittal FLAIR

image shows mass ( Ú ) to have hyperintense signal. Note

normal signal intensity of the surrounding opercular cortex

( Ú ). C. Axial FLAIR weighted image shows hyperintense

mass involving the right insular cortex. Note sharply

marginated medial border of the mass ( Ú ) abutting the

adjacent extreme capsule.

Fig 12. Recurrent pilocytic

astrocytoma. A. Sagittal

noncontrast T1-weighted image

through the right insular cortex

demonstrates isointense mass

( Ú ) adjacent to the posterior

insular cortex. B. Sagittal

postgadolinium study shows

homogeneous enhancement of

mass. C. Axial FLAIR image

shows mass ( Ú ) in subinsular

area sparing the posterior

insular cortex( Ú ) D. Coronal

postgadolinium study shows

enhancing mass within the

subinsular cortex with rounded

medial border of the mass.

Fig 8. Recurrent Low grade astrocytoma.

A. Sagittal noncontrast T1-weighted

image through the right insular cortex

demonstrates hypointense expansile

mass ( Ú ) occupying insular cortex.

Note involvement of the adjacent

superior frontoopercular cortex ( Ú ) and

temporoopercular cortex ( Ú ). B. Sagittal

FLAIR image shows entire mass to be

uniformly hyperintense ( Ú ) C. Coronal

T2-weighted image demonstrates

expansile mass ( Ú )along the right insular cortex with sharply deined medial extension. There is adjacent superior spread of the mass

along the frontoopercular cortex ( Ú ), inferiorly along the temporopercular cortex ( Ú ) and medially along the substantia innominata ( * ).

Note previous surgery with enlarged subarachnoid space of the right Sylvian issure (Ú)

Fig 13. Low grade glioma. A. Sagittal noncontrast

T1-weighted image shows focal mass ( Ú ) in the right

frontoparietal operculum. B. Coronal FLAIR image

shows expansile hyperintense mass involving the

opercular cortex

Fig 14. Glioma. A. Sagittal noncontrast T1-weighted image through

the left insular cortex demonstrate focal mass ( Ú ) involving the left

anterior temporal operculum. Notice elevation of the entire insular

cortex ( Ú ). B. Coronal postgadolinium image shows mass primarily in

left temporoopercular cortex. There is medial and superior extension

to the adjacent insular cortex ( Ú ) and elevation of the sylvian cistern

REFERENCES:

1. Augustine JR: The insular lobe in primates including

humans. Neurol Res 7: 2-10, 1985.

Fig 9. Recurrent pilocytic astrocytoma. A. Sagittal

noncontrast T1-weighted image through the right

insular cortex demonstrates isointense mass ( Ú )

occupying the anterior insular cortex. B. Sagittal

postgadolinium study demonstrates ring enhancement.

C. Axial postgadoliunium T1-weighted image shows

exact location of mass and note sharp linear border

abutting the extreme capsule

Fig 15.

Glioblastoma.

A. Sagittal

noncontrast

T1-weighted

image

through right

insular cortex

demonstrate

large mass involving the right temporal lobe. Discrete zones of

hyperintensity suggesting hemorrhage within the mass is seen.

Note elevation of the right insular cortex. B. Sagittal postgadolinium

image shows multilobulated area of rim enhancement of the mass.

Fig 16. Cerebral

metastases.

A. Sagittal

noncontrast T1-

weighted image

through left

opercular cortex

shows focal hypointensity involving the temporal lobe ( Ú ). B.

Sagittal postgadolinium T1-weighted image shows homogeneously

enhancing mass involving the temporoopercular cortex with

surrounding vasogenic edema. C. Coronal postgadolinium image

shows enhancing mass in left temporoopercular cortex with

elevation of Sylvian issure ( Ú )

2. Cunningham DJ: The development of the gyri and sulci

on the surface of the island of Reil of the human brain.

J Anat Phys 25:338-347, 1890-1891.

3. Osborn AG: Diagnostic Neuroradiology, ed 1. St. Louis:

Mosby, Inc, 1994, pp 136-138.

4. Reil JC: Die Sylvische Grube. Arch Physiol 9:195-208,

1809.

5. Ture U, Yasargil DCH, Al-Mefty O, Yasargil GM:

Topographic anatomy of the insular region. J

Neurosurg 90:720-733, 1999.

Fig 18. Left

sphenoid wing

meningioma.

A. Sagittal

noncontrast

T1-weighted

image through

the left insular

cortex shows an extradural isointense mass ( Ú ) posterior

to the sphenoid wing. Notice posterior displacement ( Ú )

and superior elevation (Ú) of the insular cortex. B. Axial

postgadolinium image shows homogeneously enhancing

extradural mass with posterior displacement of the

Sylvian issure. Notice marked hypointensity of the white

matter suggesting vasogenic edema ( Ú )

6. Ture U, Yasargil GM, Al-Mefty O, Yasargil DCH: Arteries

of the insula. J Neurosurg 92:676-687, 2000.

Fig 11. Left MCA infarct involving both trunks of

MCA. A. Sagittal contrast T1-weighted image

through the left insular cortex shows diffuse

involvement of the insular cortex ( Ú ). Note

swelling of adjacent cortex of the frontoorbital

opercular ( Ú ), frontoparietal opercular (Ú) and

temporoopercular cortex ( Ú ). B. Axial diffusion

weighted image show restricted diffusion involving

the entire insular cortex ( Ú ) and adjacent

opercular and supericial cortex. ( Ú )

7. Wolf BS, Huang YP: The insula and deep middle

cerebral venous drainage system: normal anatomy and

angiography. AJR 90:472-489, 1963.

Fig 10. Left MCA infarct involving inferior trunk. A. Sagittal noncontrast

T1-weighted image through the left insular cortex shows distinct regions of

hypointensity involving the posterior insular cortex ( Ú ) and the surrounding

opercular cortex ( Ú ) . Note hypointensity of the cortex of the posterior frontal

and parietal lobes (Ú). B. Sagittal postgadolinium study shows slow low

( Ú ) through the inferior trunk branches of the middle cerebral arteries. C.

Axial diffusion weighted image shows area of restricted diffusion involving the

posterior insular cortex ( Ú ) and adjacent opercular and supericial cortex ( Ú )

Fig 17. Cerebral abscess. A. Sagittal T1-weighted image through the left

insular cortex demonstrate multiple areas of abnormalities around the insular

cortex. B. Sagittal postgadolinium T1-weighted image shows multiple ring

enhancing masses throughout the brain parenchyma. Note enhancing mass

in the right frontoorbital operculum. ( Ú ) C. Axial postgadolinium image shows

the corresponding mass in the frontoorbital operculum ( Ú ). Note multiple ring

enhancing masses throughout the brain

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