General
- Aka lateral sulcus
- Formed by the infolding of the frontal, parietal, and temporal opercula over the insula
- Due to a phenomenon called Yakovlevian torque, the sylvian fissure is often longer and less curved on the left hemisphere than on the right.
Craniometrics
Sylvian Fissure
- Approximated by a line connecting the lateral canthus to the point 3/4 of the way posterior along the arc running over convexity from nasion to inion (TH lines).
- On the skull (once it is exposed in surgery): the anterior portion of the Sylvian fissure follows the squamosal suture and then deviates superiorly to terminate at Chater's point, which is located 6cm above the EAM on a line perpendicular to the orbitomeatal line; it is also ≈ 1.5cm above the squamosal
Borders
Anterior wall
- Fronto-temporal arachnoid membrane (black arrow heads)
- Bridges the anterior portion of the planum polare to the posterior portion of the lateral, posterior, and medial orbital gyri
- Continues medially with the arachnoidal membrane of the carotid, olfactory, and chiasmatic cisterns
- Arrowheads indicate the frontotemporal arachnoid reflection bridging the orbital surface of the frontal lobe to the planum polare
- Intraoperative photograph showing the basal surface of the right hemisphere after the pterional craniotomy and dural opening.
- The frontotemporal arachnoid membrane (arrows) in this figure has been stretched between the tip of the bipolar forceps and the suction tube. The frontotemporal arachnoid membrane is continuous with the carotid, chiasmatic, and olfactory cisterns.
- In this figure, the olfactory tract is shown at the right side of the tip of the suction tube, and the optic nerve is shown at the right side of the olfactory tract.
- Standard pterional approach
- Intraoperative photograph displaying cerebral exposure after a standard right pterional craniotomy. The tip of the suction tube has retracted the pars triangularis medially.
- 1, Posterior orbital gyrus;
- 2, Lateral orbital gyrus (pars orbitalis).
- The blue arrowheads indicate frontotemporal arachnoid reflection on the basal surface.
- The black arrowheads indicate frontotemporal arachnoid reflection on the lateral surface.
- The frontotemporal arachnoid membrane has been split to display the anterior opercular compartment of the sylvian fissure on the basal surface.
- 1, Lesser wing of the sphenoid;
- 2, Planum polare;
- 3, Insular apex.
- The posterior orbital gyrus is retracted medially by the tip of the suction tube.
- The black arrowheads indicate the frontotemporal arachnoid membrane.
- The blue arrow indicates the beginning of the anterior insular cleft.
- The frontotemporal arachnoid membrane and the anterior opercular compartment have been further split to display the anterior insular compartment.
- The M1 segment of the MCA courses in the lower part of the anterior operculoinsular compartment (sphenoidal compartment).
- The blue arrow indicates the anterior insular cleft
1, Anterior orbital gyrus;
2, Lateral orbital gyrus;
3, Rectus gyrus;
4, Posterior orbital gyrus
Floor
- Temporal operculum (the 3 transverse temporal gyri)
- Comprises, from posterior to anterior,
- Planum temporale
- Composed of
- Middle and posterior transverse temporal gyrus
- Overlies the supra marginal gyrus
- Composed of middle and posterior transverse parietal gyri
- Heschl’s gyrus (anterior transverse temporal gyrus)
- Overlies the post central gyri
- Planum polare
- Overlies the
- Precentral gyrus
- Pars opercularis
- Pars triangularis
- 1, Cuneous
- 2, Posterior transverse temporal gyrus
- 3, Parahippocampal gyrus
- 4, Middle transverse temporal gyrus
- 5, Heschl's gyrus
- 6, Hippocampal head
- 7, Planum polare
- 8, Uncus
- 9, Superior temporal gyrus
Roof
- Frontal operculum: consist of
- Gyri of the frontal lobe
- Basal surface of hemisphere: lateral and posterior medial orbital gyri on the basal surface
- Lateral surface of hemisphere:
- Pars orbitalis
- Formed by the posterior part of the lateral orbital gyrus and the lateral part of the posterior orbital gyrus
- Pars triangularis
- It is here that the basal part and the lateral part of the sylvian fissure separates into.
- Pars opercularis
- Precentral gyrus
- Gyri of the parietal lobe
- Postcentral gyri
- Supramarginal gyri
- Lateral view of the left cerebral hemisphere.
- 1, Pars triangularis of the inferior frontal gyrus;
- 2, Precentral gyrus;
- 3, Postcentral gyrus;
- 4, Supramarginal gyrus;
- 5, Pars orbitalis;
- 6, Pars opercularis;
- 7, Junction between the superior temporal gyrus and the Heschl’s gyrus;
- 8, External acoustic meatus.
- *, at this point, the planum polare starts to deviate medially.
- Note the large space in the sylvian fissure between the structures 1, 5, and 6.
- At the surface of the left hemisphere.
- *, projection of the external acoustic meatus.
- At the opercular level of the left hemisphere. Heschl’s gyrus (arrow). 1, Postcentral gyrus.
- Anterobasal view of the cerebrum.
- 1, Pars triangularis
- 2, Pars orbitalis
- 3, Pars opercularis
- 4, Precentral gyrus
- Large arrow: where the medial deviation of the planum polare begins.
- Small arrow: where the medial deviation of the planum polare intensifies.
- Superior view of the left hemisphere.
- An axial cut has been made to expose the lateral ventricle.
- The frontal and parietal opercula have been removed to expose the insula and the temporal opercula.
- 1, Rostrum of the corpus callosum;
- 2, Head of the caudate nucleus;
- 3, Planum polare;
- 4, Insula;
- 5, Thalamus;
- 6, Heschl’s gyrus;
- 7, Choroid plexus of the atrium of the lateral ventricle covering the pulvinar of the thalamus;
- 8, Middle transverse temporal gyrus;
- 9, Posterior transverse temporal gyrus.
- The arrow indicates the medial end of the Heschl’s gyrus that points toward the posterior limb of the internal capsule and toward the atrium of the lateral ventricle.
- The arrowheads indicate the location of the angiographic sylvian point.
- 1, Precentral gyrus
- 2, Post central gyrus
- 3, Supramarginal gyrus
- 4, Inferior frontal sulcus
- 5, Pars opercularis of inferior frontal gyrus
- 6, Superior temporal gyrus
- 7, Pars triangularis of inferior frontal gyrus
- Arrowheads: posterior ramus of the sylvian fissure
- Arrow: ascending and descending terminal branches of the posterior ramus of the sylvian fissure.
- Transverse cut has been made by following a line drawn from the base of the pars triangularis of the inferior frontal gyrus to the supramarginal gyrus, immediately above the posterior ramus of the sylvian fissure
- 1, Frontal horn of lateral ventricle
- 2, Caudate head
- 3, Atrium
- 4, Pars triangularis
- 5, Pars opercularis
- 6, Precentral gyrus
- 7, Post central gyrus
- 8, Supramarginal gyrus
- 9, Superior temporal gyrus
- The operculum of the supramarginal gyrus has been removed to display the middle and posterior transverse temporal gyri and the medial end of the Heschl’s gyrus
- 1, Medial part of the Heschl’s gyrus
- 2, Middle transverse temporal gyrus
- 3, Posterior transverse temporal gyrus
- 4, Precentral gyrus
- 5, Postcentral gyrus
- 6, Posterior end of the superior temporal gyrus turning around the descending
- branch of the posterior ramus of the sylvian fissure to become the supramarginal gyrus
- 7, Superior temporal gyrus
- Operculum of the postcentral gyrus has been removed to display the Heschl’s gyrus and posterior end of the insula
- 1, Insula's posterior long gyrus
- 2, Heschl's gyrus
- 3, Middle transverse temporal gyrus
- 4, Posterior transverse temporal gyrus
- 5, Pars opercularis
- 6, Precentral gyrus
- 7, Supramarginal gyrus
- 8, Superior temporal gyrus
- The operculum of the precentral gyrus has been removed to display the posterior part of the planum polare, located immediately anterior to the Heschl’s gyrus, and also to display the posterior half of the insula.
- 1, Posterior long gyrus of insula
- 2, Pars triangularis
- 3, Pars Opercularis
- 4, Heschl's gyrus
- 5, Middle transverse gyrus
- 6, Posterior transverse gyrus
- 7, Planum polare
- 8, Superior temporal gyrus
- The pars opercularis of the inferior frontal gyrus has been removed to display the anterior portion of the planum polare and the anterior portion of the insula
- 1, Insula
- 2, Pars triangularis
- 3, Heschl's gyrus
- 4, Planum polare
Posterior wall
- Supramarginal Gyrus
- The posterior ramus of the Sylvian fissure is directed backward and turns sharply upward to terminate in the inferior parietal lobule.
- The supramarginal gyrus is the structure that wraps around the upturned posterior end of the Sylvian fissure.
- This gyrus forms the most posterior opercular lips of the fissure.
- Parietal Lobe Operculum
- The postcentral gyrus is usually the next gyrus along the fissure anterior to the supramarginal gyrus.
- Superior temporal gyrus
Formed of two parts
Superficial part
- Lateral part of the sylvian fissure
- At the level of the tip of the pars triangularis (at anterior sylvian point) it has 3 main rami (a continuation of the sylvian fissure)
- Anterior horizontal rami
- Anterior ascending rami
- Anterior horizontal and the anterior ascending rami delimit the pars triangularis of the inferior frontal gyrus
- Posterior rami
- Longest rami
- Separating the frontal and parietal lobes superiorly from the temporal lobe inferiorly
- IRP: Inferior rolandic point
- AAR: anterior ascending rami
- HR: horizontal rami
- Anterior sylvian point: The confluence of the anterior horizontal, anterior ascending, and posterior rami of the superficial part of the Sylvian fissure forms the anterior Sylvian point
- The distance between the anterior sylvian point (ASyP) and the IRP along the sylvian fissure (SF) is 2.3 cm.
- IRP is 2.5 cm posterior to the pterion on the sylvian fissure line.
- This point is situated 2-2.5 cm posterior to the Anterior Sylvian Point (ASP).
- A spatula has been placed in the horizontal ramus of the sylvian fissure that continues medially with the anterior limiting sulcus of the insula. The precentral gyrus is usually related to the mid-posterior portion of the insula.
- 1, Precentral gyrus
- 2, Frontal horn
- 3, Anterior limiting sulcus of the insula
- 4, Junction between the inferior and the superior limiting sulci of the insula
- 5, Anterior portion of the insula
- 6, Pars orbitalis
- 7, Heschl’s gyrus
Images
Deep part
- Anterior Operculoinsular compartment (anterior part of the sylvian fissure)
- Aka Sphenoidal compartment
- Located
- On basal surface
- In the region of the limen insulae
- At the lateral margin of the anterior perforated substance
- Near the lesser wing of sphenoid bone
- It is a narrow space posterior to the sphenoid ridge between the frontal and temporal lobes that communicates medially with the carotid cistern
- Lateral Operculoinsular compartment (arrow heads) (Lateral part of the sylvian fissure)
- Location
- On lateral surface
- Between
- Opercular cleft (between the opposing lips of the frontoparietal and temporal operculae)
- Insular cleft (with a superior limb located between the insula and frontoparietal opercula, and an inferior limb between the insula and temporal operculum)
- Near the anterior surface of insula
Variants of the Sylvian fissure
- As described by Yasargil
- Type I: Wide and straight Sylvian fissure (SF).
- Type II: Wide SF with herniation of the frontal and/or temporal opercula.
- Type III: Narrow and straight SF.
- Type IV: Narrow SF with herniation of the frontal and/or temporal opercula.
- Clinical significance
- A narrow fissure (Type III and IV) or herniated opercula increases surgical difficulty.
Sylvian cistern contains 3 parts
- Fissure
- Divided into
- Anterior (Sylvian fissure stem ) compartments
- Anterior part of the sylvian fissure
- Located on basal surface
- Proceeds laterally and anteriorly toward the lateral surface of the brain.
- Covered anteriorly by the frontotemporal arachnoid membrane
- The stem originates inferiorly just lateral to the anterior perforated substance, between the lateral olfactory stria and the rhinal incisura or temporal incisura
- Extends laterally towards the temporal pole and as it extends laterally it divides into the
- Ascending rami
- Horizontal rami
- Posterior rami
- Confluence of these rami has been referred to as the “Sylvian point”
- Posterior (insuloopercular) compartments
- Opercular sulci
Frontal opercula | Parietal opercula |
Inferior frontal and precentral gyri | Planum polare |
Postcentral gyri | Heschl's |
Supramarginal gyrus | Planum temporale |
- Sylvian fossa
- Houses the MCA that is just superficial to the insula
MCA
- Divided in 4 segments:
- M1 segment courses posterior and parallel to the sphenoid ridge,
- The course of the M1 segment (3-4 cm in length) within the proximal Sylvian fissure is C- or S-shaped.
- There are a number of anatomic variations in MCA branching, and familiarity with these anatomic variations is important for surgery of neighboring lesions.
- The dissection should be conducted along the inferior and anterior aspect of the M1 to prevent inadvertent injury to the lenticulostriate arteries.
- M2 segment resides on the limen insula,
- M3 segment spreads over the frontotemporoparietal opercula
- M4 segment is composed of the branches to the cerebral convexity.
- Adequate exploration of the MCA at the point of its origin from the internal carotid artery through its bifurcation will allow appropriate identification of the surgical vascular anatomy and preservation of normal structures during surgery in this region.
Surgical significance
- There is a dense network of pia-arachnoid fibers around the arteries, veins, and pial surfaces of the adjacent opercula and insular gyri of the entire fissure
- The proximal section of the fissure (vallecula) houses the internal carotid artery bifurcation and limen insula, where the MCA bifurcates into its superior and inferior trunks.
- The vallecula also contains lateral lenticulostriate perforators and the deep Sylvian vein.
- Opening of the vallecula will provide space to reach the proximal MCA and internal carotid artery bifurcation territories.
- The proximal (sphenoidal) section A also includes the area (3–4 cm) over the planum polare where the pial surfaces can be highly adherent, requiring gentle microdissection. The paucity of the vessels in this section allows adherence of the frontotemporal opercula.
- The middle (insular) section B is 6 to 7 cm in length and extends from the limen insula to the posterior insular point. In this section of the fissure, the sulci are less interdigitated, possibly simplifying fissure dissection.
- The posterior (retrosinsular) section C is short (4–5 cm) but deep, and covered by the supramarginal, transverse temporal, and transverse parietal gyri.
- The dissection can be especially challenging at this segment because of complex interdigitations of the opercula.
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