Sylvian approaches

Indicated

Aneurysm

MCA
Ophthalmic

Insular tumour
Medial temporal lobe tumour

Sylvian point: great places to access the sylvian fissure as there is more arachnoid space to enter the slyian space

Dissect from inside to outside (like opening an orange) as you have better appreciation of the dissection plane.

Sylvian Fissure Split

Proximal to distal or distal only

Tailored to the pathology addressed

“Inside to Outside” technique important

Yasargil “go from inside out and play with nature”
An extension of cisternal surgery
Aneurysms
Insular tumors
Giant aneurysms

Direct localization and selective split (don’t overdissect):

Neuropsychological implications
Cavernous Malformation
Unruptured MCA aneurysm

Technical Nuances

High Magnification
Sharp Dissection (cultural variation here)!!!

Don’t pull on arachnoid!
Bipolar dissection

Use both hands- bimanual technique

Sucker tip as important assist, and dynamic retractor
Tension on arachnoid membranes to identify which ones need to be cut

Preserve Veins

Always preserve confluence with sphenoparietal sinus!
Sometimes ligate side branches

Open what you need only

Focused opening

Use retractors when necessary

Gentle holding of conquered territories
Giant aneurysms
Revascularization

Splitting fissure

Always open arachnoid with sylvan vein on frontal side
1st nerve you see is the 3rd not optic as the fissure slop down inferiorly when you split it

Normal variations of the superficial sylvian vein anatomy (right side).

(A) Absence of superficial sylvian veins.

(B) Single superficial sylvian vein.

(D) Complex network of superficial sylvian veins.

Venous systems draining the sylvian fissure:

(A) Superior

(B) Anterior

(D) Mixed systems

Types of sylvian fissures.

(A) Atrophic fissures in older patients are wide open with minimal contact between the frontal and temporal lobes.

(B) Apposed fissures are more common with large areas of contact between the frontal and temporal lobes.

Interdigitated fissures, either frontal-herniating (C) or temporal-herniating

(D) are tightly apposed with contoured areas of contact, and the angle of approach must follow this rolling contour.

Sylvian fissure dissection

Positioning

Supine
Head rotated away from the side of the surgery approximately 30 degrees.

Turning the head more than 30 degrees may obstruct fissure dissection by rotating the temporal opercula onto the angle of fissure dissection

FIGURE 5. A transparent view of the fissure and its orientation relative to the skull and head position is demonstrated far A and closeup B views). Used with permission from Neurosurgical Atlas by Aaron Cohen-Gadol, MD. — A transparent view of the fissure and its orientation relative to the skull and head position is demonstrated (far A and closeup B views). Used with permission from Neurosurgical Atlas by Aaron Cohen-Gadol, MD.

Frontotemporal (pterional) approach

Drilling the sphenoid wing as far down as the superior orbital fissure with or without the removal of the anterior clinoid process,

After the dural opening, further brain relaxation may be immediately achieved by gentle elevation of the anterior frontal lobe and opening the arachnoid membranes over the opticocarotid cisterns.

Visualisation of basilar artery after opening the membrane of liliequist.

A small cotton ball may be inserted underneath the frontal lobe to maintain the outflow of cerebrospinal fluid from these cisterns during fissure dissection.
Cover the surface of the brain, except the peri-insular areas, with pieces of moist Telfa to avoid heat injury to the cortex from the intense light of the microscope.
The Sylvian fissure is covered along its entire length with a thick band of arachnoid membrane.
The superficial Sylvian veins outline the course of the fissure.
In the absence of the veins, identification of the fissure may be difficult;

In such cases, recognition of the M4 branches exiting the fissure onto the cortex may be helpful.

The fissure is 10 to 14 cm in length, longer than appreciated.
Minor or subtle forms of cortical malformation can transform the fissure into a series of sulci, making the operator’s job very difficult.
The Sylvian fissure is more readily split by conducting dissection above rather than below the superior Sylvian vein since the vein travels approximately 4 mm below the fissure in more than 80% of the hemispheres (Figures 6 and 7).

FIGURE 7. The Sylt.'ianfissure is split using the inside-to-outside technique. The dissection is started at rhe Sylvian point and extended 'o rhe depth of the fissure $0 that one can identify distal MCA branches on the surface Of the Next, rhe dissection continues from deep to superficial (upper image, inset, arrows). This method of opening the fissure has an analogy: Yasargil compared this method to radial Splitting of peeled orange wedges. Ir is difficult m separate the edges from the outside lower image), bur it is easy put rhe finger into the middle Of the orange and radially separate the wedges (right lower image). Used with permission from Neurosurgical Atlas by Aaron Cohen-Gadol, MD. — The Sylvian fissure is split using the inside-to-outside technique. The dissection is started at the Sylvian point and extended to the depth of the fissure so that one can identify distal MCA branches on the surface of the insula. Next, the dissection continues from deep to superficial (upper image, inset, arrows). This method of opening the fissure has an analogy. Yasargil compared this method to radial splitting of peeled orange wedges. It is difficult to separate the edges from the outside (left lower image), but it is easy to put the finger into the middle of the orange and radially separate the wedges (right lower image). Used with permission from Neurosurgical Atlas by Aaron Cohen-Gadol, MD.

FIGURE 8. Step l. The superficial fissure is dissected open the level Of the Sylvian point Where the interopercular S/utce through the arachnoid band is most prominent. This dissection is extended to the level b•f2 branches and insula. Note the use Of the small cotton pledget discussed above. Used With permission from Neurosurgical Atlas by Aaron Cohen-Gail, MD. — Step 1. The superficial fissure is dissected open at the level of the Sylvian point where the interopercular space through the arachnoid band is most prominent. This dissection is extended to the level of the M2 branches and insula. Note the use of the small cotton pledget discussed above. Used with permission from Neurosurgical Atlas by Aaron Cohen-Gadol, MD.

The arachnoid of the fissure should preferably be opened on the frontal side of the veins

So that the veins will not cross the fissure when the frontal lobe in elevated.

Venous anatomy is quite variable, and caution is advised against a dogmatic agenda for execution of the split.

If more than one superficial Sylvian vein is present, the dissection should proceed between the 2 veins because these veins are encased by arachnoid bands that are typically more robust than the pia.
There is often no bridging vein between the superficial Sylvian veins, and therefore the small fronto-orbital tributary veins to the superficial Sylvian vein are less likely to be sacrificed during fissure opening.
Preservation of the veins during fissure dissection protects cerebral venous drainage and voids venous infarction;

Especially important if the veins seem to be dominant (larger caliber and parasagittal veins or vein of Labbe are less prominent on preoperative angiography)

Open sylvian fissure at the Sylvian point (apex of the pars triangularis)

Because

Gives the widest transfissure corridor where the superficial arachnoid membrane is demarcated;
Allows you to find the insular apex, an important landmark for surgical orientation.

Using a round blade (beaver knife), a small (3-mm) opening along and above the superficial Sylvian vein is made.

The superficial arachnoid membrane along the fissure may be incised at several points in a similar fashion.

2 short, fine bipolar or jeweler forceps used to creat an opening through the arachnoid by holding the edges of the arachnoid and then spreading the arachnoid.

This strips the arachnoid over the vein and splitting the superficial fibers of the fissure.

If slight pial bleeding is encountered, hemostasis is achieved using a minute piece of Gelfoam covered with a small cotton pledget,

Bipolar coagulation is avoided during the entire fissure dissection, if possible.
Exploration may be conducted a few millimeters further in the neighborhood of the oozing pial surface. The surgeon then may return to this region in a short period of time to appreciate the spontaneous hemostasis obtained using this technique.

Soft retraction using

Soft, moist, cotton pledgets (1 × 1 mm) or balls are gently glided between the pial membranes of the adjacent gyri.
Gradual and gentle compression over the pledgets by the fine suction tube, in addition to the spread action of the bipolar forceps, will allow gradual extension of the initial opening down to the Sylvian fossa.
A slightly larger pledget is introduced into the initial window to replace the smaller pledget as the fissure opening is enlarged and deepened.

The larger pledget can keep this segment of the fissure open as dissection is continued anteriorly without the need for retractors.

One should split the fissure deep enough to identify the

MCA branches
Insula in the Sylvian fossa

Open the fissure from “inside to outside.” manner.

It is often more difficult to separate orange slices from outside the orange, but if one starts by entering into the center of the orange and identifying the dividing planes of the wedges from inside, one can split the slices more readily without compressing the individual slices and releasing their juice.
The inside-to-outside technique allows early identification of the MCA branches, therefore allowing the surgeon to adjust the plane of dissection along the interdigitating opercula while maintaining the depth of the fissure as a landmark for orientation.
The contours of the interdigitating opercula rarely follow a straight vertical line as the lateral orbital gyrus indents the proximal superior temporal gyrus and temporal pole, causing a C or S- shaped course of proximal fissure in the coronal plane.
Early identification of the undulating pial and arachnoid planes from inside the fissure simplifies dissection tremendously.

As the fissure is opened toward the surface, the thicker superficial arachnoid membranes may be cut using microscissors.

Following identification of the MCA branches and insula deep at the Sylvian point, anterograde inside-to-outside dissection continues.
Injection of saline solution using a syringe deep into and along the Sylvian fossa can expand this fossa, facilitating the identification of the arachnoid planes between the pial banks.
The jeweler’s forceps with fine tips can be used to grab and separate the more superficial thick arachnoid bands, when needed.
Deeper dissection proceeds using straight (nonbayoneted) microscissors and bipolar forceps (5-mm tips).

Through the alternating use of

Bipolar forceps to spread the thin arachnoid layers,
Microscissors to transect thick ones, the initial fissure opening is enlarged.

Forceful blunt dissection or separation of the thick arachnoid bands or adherent pial banks using the spreading action of the forceps will lead to pial injury and bleeding.
The use of bipolar coagulation to stop pial bleeding may actually lead to further cortical injury and further bleeding.

The planum polare or the flatter surface of the anterior fissure on the temporal side may be very adherent to the frontal lobe.

Patient microsurgical dissection is warranted.
Thick arachnoid layers cover the most anterior limb of the fissure just behind the sphenoid wing;
Sharp dissection in this area may require sacrifice of one of the superior Sylvian vein branches.
As the more proximal part of the fissure is split, the MCA bifurcation and the M1 branch are identified and a more medial dissection along this artery will allow expansion of the vallecula and creation of a surgical corridor toward the opticocarotid cisterns
The posterior frontal operculum often tends to herniate into the transsylvian corridor; its aggressive retraction leads to its venous congestion, and spontaneous cortical bleeding must be avoided
Along the medial aspect of the Sylvian fissure and just before reaching the opticocarotid cisterns anteriorly, a thick arachnoid band tethers the frontal and temporal lobes to each other

This band and its occasional encasing small vein are transected
A “T”shaped arachnoid incision is made over the opticocarotid cisterns with the anterior limb of the incision just lateral to the optic nerve and over the carotid artery. This incision is further extended medially to disconnect the posterior gyrus rectus from the chiasm.
The posterior limb of the “T” incision can parallel the approximate course of the posterior communicating artery and connects with the arachnoid opening along the medial sylvian fissure.

The commonly used “outside-to-inside” technique is typically more difficult to perform because of the adherence of the frontotemporal opercula and the lack of any landmarks to guide dissection within the interdigitating opercula.
After extension and completion of Sylvian fissure dissection more medially along the distal M1 segment, the temporal operculum is mobilized away from the insula. The presence of MCA branches between the temporal operculum and the insula facilitates mobilization of the temporal operculum more than the frontal operculum. The superior and inferior peri-insular sulci can be identified, if necessary.
The M1 branch may be used as a landmark to reach the opticocarotid cisterns and the internal carotid artery bifurcation.

Distal Fissure Dissection

Distal fissure dissection is often limited because of adherence of the posterior opercula at this level;
Aggressive manipulation in this area will place the superior temporal gyrus at risk of injury;
This can be a factor especially in the dominant hemisphere.
Dissection of the posterior fissures is necessary only for

Large insular tumours
M2/M3 aneurysms
Giant MCA bifurcation aneurysms

A round arachnoid knife may be used to work within the adherent pial surfaces.
Gentle dynamic retraction of the frontotemporal opercula and anterior-to-posterior working angles often provide good exposure of the

Retrosylvian fossa
Posterior insular cortex
Periinsular sulci
Posterior M2 branches

Pearls and Pitfalls

Proximal to distal splitting is better than distal to proximal splitting

Proximal to distal

Requires significant frontal lobe retraction as the M1 is identified early and followed toward its distal pathway

Distal-to-proximal

Does not provide early proximal control and poses certain risks, especially in the case of a ruptured aneurysm

Repeated strokes on the pia by the shaft of the suction during dynamic retraction should be avoided.

The suction should be “parked” at a strategic point for mobilization of each segment of the opercula and only moved if necessary

The tip of closed microscissors is used as a dissecting tool and the jaws for transection of the thick arachnoid bands
The fissure is not perpendicular to the insula but is oblique as dissection proceeds in the posterior to anterior direction

One should not inadvertently violate the frontal pial banks while wandering within the fissure

Techniques to make dissection easier

Dynamic retraction
Sharp dissection
Microscope’s mouth switch through the inside-to-outside technique

Reference