**Abstract**

Sphenoid wing meningiomas account for 11%-20% of all intracranial meningiomas, whereas meningiomas of the anterior clinoid process comprise about 34.0–43.9%. Assignment of these cranio-basal tumors to a separate group is due to the parasellar location and challenges in their surgical removal, mainly because of its anatomical syntopy: compression of the optic nerve, carotid artery inclusion, and invasion to the cavernous sinus. This chapter consists of the combination of current knowledge and our experience in understanding, diagnosis, surgical strategy, and complication avoidance with these tumors.

**Keywords:** sphenoid wing meningioma, classification, anterior clinoid process, clinoidectomy, parasellar syntopy, pterional approach, fronto-lateral approach, skull base

### **1. Introduction**

Meningiomas are the most common primary intracranial tumors accounting for 20% of all intracranial neoplasms. Sphenoid wing meningiomas (SWM) account for 11%-20% of all intracranial meningiomas. Meningiomas of the anterior clinoid process (MAC) comprise about 34.0–43.9% of all sphenoid wing meningiomas. There is female prevalence among patients [1–3].

The challenges start with the definition of MAC. From the early beginning, H. Cushing and Eisenhardt in 1938 were the first to divide SWM into globoid tumors with a nodular shape and en plaque tumors, which are flat and spread along the sphenoid wing [2]. The globoid tumors were then categorized into lateral, middle, and medial. The last group could be classified as MAC. In accordance with Al-Mefti, MAC was classified into 3 groups according to the side of their origin on the surface of the clinoid process. First group meningiomas arise from the subclinoidal dura at the most proximal point of intradural entry of the internal carotid artery, before the carotid enters into the arachnoidal cisternal space. The second group clinoidal meningiomas originates from the superolateral aspect of the anterior clinoid process. The third group originates from the region of the optic foramen and extends into the optic canal [1, 4]. Many authors consider this classification hard to apply in daily practice. Russell & Benjamin took into account the invasion of the tumor into the lesser sphenoid wing and spread into the cavernous sinus [3]. Both parameters have great practical significance in surgical approach planning [5].

The exclusion method is also useful to identify the MAC. All paraoptic meningiomas such as tuberculum sella, diaphragm, cavernous sinus, planum sphenoidale, as well as spheno-orbital are recognizable with their specific findings [6, 7, 9]. We

#### **Figure 1.**

*Anterior clinoid bone anatomy, right side. 1 – Optic canal; 2 – Superior orbital fissure; 3 – Anterior clinoid process.*

consider the presence of the anterior clinoid process in the center of the tumor bone attachment to be the main feature of clinoidal meningiomas (**Figure 1**). The second apparent peculiarity is the paramedian location of the tumor and consequently the displaced ipsilateral optic nerve, III nerve, and the ICA toward the midline [8–10].
