Basic information
Allows the dissection of a large portion of the Sylvian fissure, and hence provides access to the anterior circulation and part of the posterior circulation.
- Assess to:
- The anterior cranial fossa
- Peri- and suprasellar regions
- Anterior third of the frontal and temporal opercula
Keep in mind
- Consider whether the patient (location of the lesion are suitable for this type of approach)
- Study carefully available images (CT, MR) to be prepared for anatomical rarities, use different section and projection
- Try to find the best route to the lesion with an avoidance of the excessive exposure and the retraction of brain tissue, otherwise use a different approach to reach the pathology
- Keep in mind the general anatomy (skin layers, temporal muscle, skull bones, brain surface, carotido-optic triangle, the circle of Willis)
- Be aware of possible slight distortion of the anatomy (patient is in the supine position and the head is rotated – effect of the gravity)
- Try to project the anatomy on the skin surface
Anatomy and important anatomical landmarks
- Skull bones – frontal, sphenoid, temporal, parietal, zygomatic, zygomatic arch, pterion
- Sphenoid wing
- Tragus, temporal muscle line
- Temporal muscle, facial nerve, superficial temporal artery, middle meningeal artery
- Brain surface (temporal, frontal lobe)
- Sylvian fissure
- Carotico-optic triangle, carotico-oculomotor triangle
- Circle of Willis
- Contralateral structures (optic nerve, carotid artery)
Highlights
Sylvian fissure, circle of Willis, optic nerve
Positioning
- Supine position
- Head rotation may change based upon the exact position of the area which must be exposed
Body positioning: supine (0°), supine lateral (45°)
Patient is positioned supine
In the case of extreme contralateral rotation, a supine lateral position can be used
Head positioning: contralateral rotation (40°), lateral tilt (10°), extension (12°)
Rotation
Contralaterally, from 15° to 60° depending on the position of the Region of Interest (ROI).
In general, more posterior and basal targets need more rotation.
Extension
From 10° to 30°, depending on the position of the ROI.
In general, more basal and anterior targets need less extension of the head.
Lateral tilt
A gentle tilt of 10° is needed to orient the vertex down.
In general, the more basal target needs less lateral tilt.
Red Flags
Avoid over-rotation of the neck by elevating the ipsilateral shoulder. Head over the heart level. Regardless the position of the target, the malar eminence must always be the highest point of the operating field.
Surgery
1. Skin incision N°22 scalpel blade
The incision should stay behind the hairline; in those patients with high hairline it is advisable to make a wider skin incision passing behind the hairline. The inferior end of the incision is placed anterior to the tragus (5 mm approx.).
The superior end is at the level of the midline. These two points must be connected with an arcuate line.
2. Initial dissection of the skin flap with elevator
Skin and pericranium can be cut and detached from the skull in one layer.
3. Placement of hemostatic clips
Avoiding an excessive cauterization of the subcutaneous layers facilitates better skin healing.
4. Skin flap elevation with elevator
It is possible to use the same techniques in this stage as were applied in the initial skin flap dissection.
5. Dissection of temporal muscle
The temporal muscle is cut with monopolar cautery along the superior temporal line attachment. Then a vertical posterior incision along the muscle’s fibers is done creating a “L” shaped myofascial incision.
6. Burr hole with perforator
A single burr hole is placed onto the pterion or behind the frontozygomatic suture.
7. Preparation of the burr holes with dura separator
This step helps to reduce the risk of tearing the dura mater during the craniotomy. The risk is higher in elderly patients because of the strong adherence between the inner table of the skull and dura.
8. Craniotomy with high-speed drill
Proceed with performing the craniotomy, paying attention to maintaining the orientation of the drill perpendicular to the skull surface.
9. Edge drilling with high-speed drill
After removing the bone flap, a fundamental step is to drill down the anterior cranial base, orbital roof and lesser wing of the sphenoid bone. Accurate drilling facilitates optimal access to the skull base and basal cistern, reducing the necessity of brain retraction.
10. Dural tenting sutures
Transosseous stitches are used to suspend the dura and reduce extradural bleeding.
11. Dura incision with N°10 scalpel blade and scissor
Dura should be incised in a C-shape and reflected toward the cranial base.
Microexploration
A1: Anterior Cerebral Artery, First Segment
AComA: Anterior Communicating Artery
A2: Anterior Cerebral Artery, Second Segment
ICA- Bif: Internal Carotid Artery (ICA) bifurcation
M1: Middle Cerebral Artery, First Segment
MCA-Bif: Middle Cerebral Artery) bifurcation
M2: Middle Cerebral Artery, Second Segment
PComA: Posterior Communicating Artery
CN I: Cranial Nerve I, Olfactory Nerve
CN II: Cranial Nerve II, Optic Nerve
CN III: Cranial Nerve III, Oculomotor Nerve
Chiasm: Optic Chiasm
MTR (anterior third): Mesial temporal region (anterior third)
Limen: Limen Insulae
Insula: Insula
ACP: Anterior Clinoid Process
PCP: Posterior Clinoid Process
LW: Lesser Wing
Closure
1. Dura reconstruction
A water-tight closure of the dura is always needed, particularly in cases of cisternal and ventricular opening. In case of dura retraction, several types of synthetic substitutes or a galea flap can be used to complete the approximation.
2. Bone fixation with microscrews
At least 3 microplates are used to guarantee the immobility of the bone flap. Immobility is necessary for osteosynthesis. For bigger craniotomies, central dural suspensions are mandatory.
3. Muscle reconstruction
Temporal muscle is sutured – this mitigates the risk of chewing problems postoperatively.
4. Subcutaneous/skin suture
Aestethic skin reconstruction is always mandatory.
