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Page 2 of 10 Alam et al. Neuroimmunol Neuroinflammation 2018;5:21 I http://dx.doi.org/10.20517/2347-8659.2017.64

Keywords: Clinoidal meningiomas, pterional craniotomy, extradural anterior clinoidectomy

INTRODUCTION
Anterior clinoidal meningiomas arise from the meningeal covering of the anterior clinoid process. In the
classical neurosurgical literature, anterior clinoidal meningiomas have not been separated from medial
[1,2]
sphenoid wing or inner sphenoid wing meningiomas . However, accumulating anatomical knowledge
and clinical experience has shown that anterior clinoidal meningiomas have unique anatomical and clinical
[2,3]
characteristics that puts them apart from meningiomas of the medial sphenoid wing . Therefore anterior
[2-4]
clinoidal meningiomas should be considered a separate clinical entity .
[5]
Visual loss is the very common presenting symptom in these tumors . The characteristic onset usually
[5,6]
occurs with unilateral failure of vision loss associated with primary optic atrophy . In some patients, loss
[7]
of vision may extend to the uninvolved eye . Visual field defects in the form of concentric narrowing of
the visual field, central scotoma, and temporal hemianopsia can be seen in patients; however, the extent
[6,8]
depends on the degree of the involvement of the chiasm and the optic nerves . Headache is another most
[9]
common symptom in these tumors, generally over the orbital or retroorbital field . Although the visual
problems are the major cause of presenting symptoms in anterior clinoidal meningiomas (45.3%, 53.3%, 58%
[9]
in some series) , this rate is not as high as in other meningiomas located in the neighboring region such as
tuberculum sellae meningiomas (75.9%-100.0%). The growth potential of the latter tumors may result in early
impingement on the optic apparatus. However, for the anterior clinoidal meningiomas, this is true only for
[10]
Al-Mefty group III tumors that encroach on the optic nerve at the optic foramen .
Several classification schemes have been proposed as methods for predicting surgical outcome. Al-Mefty’
classification of clinoidal meningiomas is based on advances in microsurgical anatomy and has been widely
accepted [11,12] . This scheme considers the origin of the tumor and its invasion pattern in the region of the
clinoid process as indicators of resectability. It differentiates among Group I, lower clinoidal meningiomas
(no arachnoidal dissection plane between the internal carotid artery (ICA) and tumor); Group II, distal or
lateral clinoidal meningiomas (which do have an arachnoidal plane between ICA and tumor) and Group III,
meningiomas that originate at the optic foramen. In Group III tumors, the arachnoidal membrane is present
[12]
between the ICA and the tumor but may be absent between the optic nerve and the tumor [Figure 1] .
Because anterior clinoidal meningiomas tend to grow upward, true invasion of the cavernous sinus is very
rare. The current literature on anterior clinoidal meningiomas documents a very wide range of cavernous
sinus invasion rates, ranging from 0 to 44.1%. We believe that this variability is, in part, a reflection of the
lack of objective and universal nomenclature among authors. This problem has led to some medial sphenoid
[13]
wing meningiomas being analyzed as part of the clinoidal group .
Based on the new classification, the coronal diameter of the tumor is combined with the classical Al-
Mefty group designation. Each tumor was graded (typed) with a numerical number denoting the Al-Mefty
[14]
grouping and a capital letter representing the tumor size on coronal section . A tumor was defined as type
A if it was measured less than 2 cm, type B if it was 2 to 4 cm, and type C (giant) if it was greater than 4 cm.
[12]
These designations were applied to each group in the current Al-Mefty classification [Figure 1] .
Many surgeons used various skull-base approaches with or without intra- or extradural removal of anterior
[14]
clinoid for resecting these challenging tumors. The recent articles by Al-Mefty , Lee et al. [15,16] described
a cranial base technique that is a modification of the original “Dolenc approach” and involves extradural
[17]
clinoidectomy, removal of the roof of the optic canal, and opening of the optic nerve sheath. Mathiesen et al.