**7.2 Extracranial steps**

The frontotemporal arciform incision starts 1 cm in front of the tragus, with the medial extent adjusted to the size of the surgical target. The scalp is progressively elevated in one layer and reclined forward, preserving the pericranial tissue for dural repair at the time of closure. A standard interfascial dissection is performed over the anterior quarter of the temporal muscle in order to spare the frontotemporal branches of the facial nerve [21, 22]. The orbital rim and zygomatic arch are progressively exposed in a subperiosteal manner. The temporal muscle is incised along the lateral orbital rim, along the superior temporal line, and at its posterior part along the skin incision. Retrograde dissection of the temporal muscle is performed using a cutting spatula from anterior to posterior and from inferior to superior in order to preserve the deep vascularization and innervation of the muscle and thus prevent postoperative atrophy [23]. Tumor-infiltrating of the muscle (1.) temporal fossa extension) must be resected at this stage. If the infratemporal fossa is invaded by the meningioma (2.) infratemporal fossa extension), the zygomatic arch must be cut anteriorly and posteriorly, maintaining its attachment to the masseter muscle, in order to recline the temporal muscle downwards as much as possible. This optional step facilitates resection of the tumor portion located in the infratemporal fossa, with particular attention to the mandibular nerve exiting the foramen ovale. In cases of major invasion of this location, the collaboration of an ear, nose, and throat surgeon is required.

#### **7.3 Cranial steps**

Depending on the extension of the intraosseous portion of the SOM, either a classical pterional craniotomy or a more complex orbitozygomatic approach is performed [24]. Guided by neuronavigation, the tumor-infiltrated bone must be resected as completely as possible using a high-speed drill and rongeurs, without overlooking the craniotomy part. The lateral wall and the roof of the orbit are drilled, initially respecting the periorbita (**Figure 5**). The intraorbital tumor extension (3.) mostly remains extraconal and can therefore be easily removed once the orbit is correctly opened. Nevertheless, the periorbit must be longitudinally opened and resected in cases of intraconal invasion [25]. If the tumor adheres too much to the cranial nerves, it is recommended to leave a residue in place to avoid postoperative deficits. The drilling continues medially at the level of the greater and lesser wings of the sphenoid bone, opening the SOF (4.), and inferiorly at the level of the floor of the middle cranial fossa, opening the foramens rotundum and ovale if necessary. With the involvement of the ACP (5.) and the invasion of the optic canal

#### **Figure 5***.*

*Intraoperative views of the resection of a left sphenoid-orbital meningioma with invasion of the anterior clinoid process (ACP), optic canal, and orbit. (a) Left pterional approach with drilling of the lesser sphenoid wing (LSW) and lateral wall of the orbit, in order to open the superior orbital fissure (SOF). The orbitotemporal periosteal fold is then identified at the external part of the SOF and divided to optimize the retraction of the frontal and temporal lobes and expose the contours of the ACP. (b) The final step of the extradural resection of the ACP. The LSW, optic strut, and roof of the optic canal were drilled before resecting the bony content inside the ACP. A thin shell of bony contour is preserved in order to remove the clinoid tip en bloc. (c) Once the drilling is completed, the orbit is properly exposed in continuity with the SOF and optic canal which have been opened. (d) The dura mater is opened in an arciform fashion, revealing the intradural portion of the meningioma (asterisk). (e) The dura mater of the optic canal is gently opened with a fine scalpel to remove the tumor fragments compressing the optic nerve at this level. (f) At the end of the procedure, the chiasma and the two optic nerves are correctly exposed. The coagulated portion of the dura mater at the level of the tuberculum sellae can be seen (asterisk; Simpson grade 2 resection).*

(6.), an extradural anterior clinoidectomy, which is carried out under magnification and constant irrigation, must be performed to optimize the decompression of the ON and prevent thermic lesions [26]. This step also allows the surgeon to extradurally split the lateral wall of the CS (7.) when there is a tumor at this level, in order to improve the devascularization of the meningioma.
