Anterior Clinoidal Meningiomas

Clinoidal meningiomas (CM) are benign tumors arising from the meningeal covering of the anterior clinoid process (ACP). These tumors have been referred to by various other terms, such as medial or inner sphenoid wing meningiomas. In the literature predating the wide use of magnetic resonance imaging (MRI), CM was often reported under the loose category of “suprasellar,” “perisellar,” “parasellar” or “anterior fossa floor” meningiomas together with meningiomas of the tuberculum sellae, middle or lateral sphenoid wing, cavernous sinus and even the anterior fossa.^1–6 In large meningiomas encompassing both the cavernous sinus (CS) and the clinoidal region, the exact site of origin, based on preoperative imaging studies, or at times even after an intraoperative inspection, is often difficult to determine. In these large tumors, the clinoidal origin is assumed in our practice if greater than two thirds of the tumor is extracavernous in location. Those tumors extending to the clinoidal region, but originating from the tuberculum sella, optic canal, orbital roof, planum sphenoidale, middle or lateral aspects of the sphenoid wing, are not considered as CM. Because of the proximity of the optic nerve (ON) to the ACP, patients with CM most commonly present with monocular visual deterioration, which is often unrecognized by patients until visual loss is severe and the tumor has reached a significant size. These tumors are often formidable to resect completely and safely, especially when their size becomes large enough to encircle, compress, and/or displace the adjacent ON, the internal carotid artery (ICA), its branches, and the oculomotor nerve. In the past, common morbidity associated with CM surgery included injury to the optic and oculomotor nerves, the ICA, and its branches. Mortality rate was as high as 32% in earlier series mainly due to major vessel injuries.⁷ Total resection was possible in only a minority of cases, leading to early tumor recurrence and further deterioration of the patient. Many neurosurgeons, even today, recognizing the relatively high incidence of poor postoperative outcome for patients with these tumors, recommend conservative subtotal resection with or without postoperative radiation therapy or even a more conservative approach, using radiation as the sole treatment.⁸ Additionally, most asymptomatic patients with CM are often observed with serial MRI scans.