**2. Epidemiological data and clinical presentation**

While meningiomas account for approximately 20% of all intracranial tumors in males and 38% in females (with a 2:1 female-to-male ratio) [9, 10], SOMs comprise between 4% and 9% of all meningiomas [11]. In a meta-analysis of 38 retrospective studies about SOM that included a total of 1486 patients, Fisher *et al.* reported a mean age of 51 ± 6 years old, with a high proportion of women (82%) [12].

In a review of the literature, Apra *et al.* demonstrated a greater female predominance in SOM (86% across 14 different series with a total of 867 patients) than in meningiomas from all locations (74% female in a total of 110,359 patients in the largest meningioma study) [13, 14]. In their own retrospective study of 175 histologically confirmed cases of SOM, women were found to be significantly younger than men at the time of diagnosis (51 ± 5 vs. 63 ± 8 years) [13]. Notably, progesterone receptors were identified much more frequently in women than in men (96% vs. 50%), and exogenous hormone intake (predominantly progesterone) was identified in 83% of women in this same series, indicating that this is a risk factor for developing SOM [13].

Patients typically present with progressive, unilateral, and nonpulsatile proptosis (84%), often associated with cosmetic deformity [12, 15]. The frequent optic nerve (ON) disturbances result in unilateral decreased visual acuity (46%), constricted visual field (31%), and sometimes loss of color vision (5%) [12]. Ophthalmoplegia is seen in 25% of patients with SOM, often due to cranial oculomotor nerves deficit (oculomotor nerve 11%; trochlear nerve 6%; abducens nerve 4%). Diplopia can also be caused by intraorbital compression of the oculomotor muscles. Deficits in other cranial nerves (trigeminal, vestibulocochlear, and facial nerves) are less common. Finally, other general neurological signs, such as headaches (25%) and epileptic seizures (4%), are observed in patients with SOM.

### **3. Preoperative assessment**

Skull radiographs were historically used to diagnose SOM by demonstrating unilateral sphenoid hyperostosis. With the emergence of computed tomography (CT) and magnetic resonance imaging (MRI), these techniques became the standard before any surgical procedure involving the removal of a SOM.

CT precisely demonstrates the bone features of the SOM, as well as its extension (**Figures 1** and **2**). Using CT, the involvement of the orbit walls, floor of the middle cranial fossa (including the foramens rotundum and ovale), SOF, ACP, and optic canal can be easily identified.

MRI completes the radiological assessment, showing the globoid or plaque-like shape of the intradural portion of the meningioma and its impact on the brain parenchyma (mass effect and edema). The epicenter of the tumor on the sphenoid wing is identified, and the specific involvement of the temporal and infratemporal fossae, orbit, SOF, optic canal, and CS is determined. At this stage, it is important to differentiate between simple involvement of the lateral wall of the CS and true intracompartment invasion. Similarly, the presence of meningioma within the optic canal or SOF should be similarly distinguished from tumor bony involvement of these structures (**Figures 1** and **2**). All of these details are critical, as they contribute to the planning of the upcoming surgical procedure for optimal tumor resection.

#### **Figure 1.**

*(a) Axial contrast-enhanced T1-weighted magnetic resonance imaging demonstrates thickening of the temporopolar dura mater on the right side, with a deviated optic nerve compared to the left side. A temporopolar arachnoid cyst is seen on the left side. (b) Axial computed tomographic scan shows hyperostosis of both the lesser and greater sphenoid wings, sparing the anterior clinoid process. Proptosis can be easily measured on axial brain slices passing through the lens on both sides, by firstly taking as reference the line joining the two lateral orbital margins. This line is then projected to the level of each cornea and the distance between these two new lines is measured, giving an accurate and relevant estimate of proptosis for follow-up.*

#### **Figure 2.**

*(a) Axial contrast-enhanced T1-weighted magnetic resonance imaging demonstrates a large right sphenoorbital meningioma with middle sphenoid wing center, invading the temporal fossa (TF), the superior orbital fissure (SOF), and the orbit (O). There was no true invasion of the optic canal (OC) by the meningioma on thin-section MRI analysis. (b) Axial computed tomographic scan shows hyperostosis of the lesser and greater sphenoid wings (L&GSW) and anterior clinoid process (ACP) on the right side.*

A comprehensive preoperative ophthalmological exam is mandatory and should include at least an objective assessment of visual acuity and field, a dilatedpupil fundus examination and ideally an optical coherence tomography (OCT). The Lancaster red-green test for assessment of oculomotor muscle function is performed according to the presence of diplopia. Accurate measurement of the

proptosis can be achieved with an exophthalmometer or with correctly oriented cerebral imaging (**Figure 1**).
