Basic information
- The most useful neurosurgical approach
- Provides an adequate exposure of the entire Sylvian fissure and allows its dissection
- Probably the resident’s first craniotomy
Access to:
- The anterior cranial fossa
- Peri-sellar and suprasellar region
- Anterior third of the frontal and temporal opercula
- Orbital gyri
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
Indications
Structures which are easily accessed through the pterional craniotomy: frontal and temporal opercula, the anterior cranial fossa, orbital gyri, peri- and suprasellar regions and vessels creating the circle of Willis.
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)
Positioning
- Usually, the supine position is preferred
- The head rotation is adapted to the exact location of the lesion
- Put the Mayfield fixation with sparing of the skin incision location
Body positioning – supine (0°), supine lateral (45°)
In case of extreme contralateral rotations of the head (generally more than 50°), a supine lateral position has to be considered in order to avoid venous compression
In addition, the head is elevated 10°- 15°over the heart, and knee are gently flexed to release the sciatic nerve
Head positioning: contralateral rotation (40°), lateral tilt (10°), extension (12°)
Rotation:
from 15° to 60°
Extension:
from 10° to 30°
Lateral tilt
of 10° is needed to orient the vertex down
In general
the final head rotation and extension are dependent on the position of the pathology (in general, more posterior and basal targets need more rotation)
Red Flags
Avoid over-rotation of the neck by elevating the ipsilateral shoulder. Regardless of the position of the lesion, the malar eminence must always bet the highest point of the operating field
Surgery
1. Skin incision
The incision should stay behind the hairline; in those patients with a 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. Skin incision should be performed in two steps: the first incision should be from the midline to the superior temporal line, full-thickness, while the second incision should be from the superior temporal line to the zygomatic arch, just skin and subcutaneous in order to spare the temporalis fascia.
Red Flags
Distance from the tragus is fundamental as a too anterior incision can damage the superficial temporal artery and, more importantly, the frontal branch of the facial nerve.
2. Initial dissection of the skin flap with elevator
In order to preserve the pericranium avoid dissecting it from the skull. Alternatively, you can leave the pericranium adherent to the skin flap.
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. Interfascial dissection with dissecting scissors
Before dissecting it is fundamental to understand the anatomy of the frontal branch of the facial nerve and its course. The temporalis muscle is covered by a superficial fascia, which consists of two layers (superficial and deep layers).
The two layers are separated anteriorly by a pad of adipose tissue. There is also a deeper fascia more attached to the skull that protects the vasculature of the temporalis (anterior, intermediate and posterior deep temporal arteries, branches of the maxillary artery) and its innervations (temporal branches of the mandibular branch of the trigeminal nerve).
Once the cutaneous flap has been reflected and the temporalis fascia is exposed, a fat pad is found approximately in the center of an imaginary line connecting the rim of the orbit with the root of the zygomatic arch. The frontal nerve runs in this pad from a deeper to a more superficial plane.
6. Incision and dissection of pericranium and temporal muscle
If the pericranium has been preserved, it can be left on the bone flap’s external surface in order to ease the reconstruction of the temporal muscle during the closure. A dissection plane must be reached beneath the fat pad by cutting the superficial layer of the temporalis fascia and dissecting beneath the fat pad until the deeper layer of this fascia is reached.
Dissecting through the fat pad increases the risk of inadvertently cutting the frontal branch of the facial nerve. After this stage, an incision on the attachment of the muscle to the superior temporal line and to the frontal process of the zygomatic bone must be made with a knife or a monopolar cautery.
Hence a subperiosteal dissection with periosteal elevator is performed and muscle is retracted anteriorly and inferiorly with hooks or retractors.
7. Burr hole with perforator
Usually, 1 to 3 burr holes are recommended for a standard pterional craniotomy. The first burr hole must be set between the superior temporal line and the frontozygomatic suture of the external orbital process; the second trepanation is performed on the most posterior extension of the superior temporal line, and the third should be made on the inferior portion of the squamous part of the temporal bone.
8. 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.
9. Craniotomy with high-speed drill
Proceed with performing the craniotomy, paying attention to maintaining the orientation of the drill perpendicular to the skull surface.
10. Edge drilling with high-speed drill
After removing the bone flap, a fundamental step is to drill the anterior cranial base, orbital roof, and lesser wing of the sphenoid bone down. The accuracy of the drilling allows perfect access to the skull base and basal cistern strongly reducing brain retraction. Before the dura opening, stitches are placed to suspend it.
11. Dural tenting sutures
Transosseous stitches are used to suspend the dura and reduce extradural bleeding.
12. Dura incision with N°10 scalpel blade and scissors
Dura should be incised in a C-shape and reflected toward the cranial base
Closure
1. Dura reconstruction
A water-tight suture of the dura is always needed, particularly in cases of cisternal and ventricular opening. In the case of dura retraction, several types of synthetic substitutes or a galea flap can be used to complete the closure.
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 and tended to mitigate the risk of chewing problems postoperatively.
4. Subcutaneous and skin suture
Aesthetic skin reconstruction is always mandatory.
