Anterior clinoid process

The anterior clinoid, which represents the terminal portion of the lesser wing of the sphenoid bone, forms the anterior aspect of the lateral wall of the optic canal.

AC: anterior clinoid process; ICA: internal carotid artery; LT: lamina terminalis; ON: optic nerve; OlN; olfactory nerve; SW: sphenoid wing; TS: tuberculum sellae; A1: A1 segment of the Anterior Cerebral Artery; A2: A2 segment of the Anterior Cerebral Artery; M1: M1 segment of the Middle Cerebral Artery

Its underlying optic strut (OS) separates the superior orbital fissure (SOF from the optic canal (OC).

ACP's anatomical location is important for its relation with neighboring structures including optic nerves, internal carotid artery (ICA), and other neurovascular structures.


The frontotemporal, so-called pterional approach has evolved with the contribution of many neurosurgeons over the past century. It has stood the test of time and has been the most commonly used transcranial approach in neurosurgery. In its current form, drilling the sphenoid wingas far down as the superior orbital fissure with or without the removal of the anterior clinoid process, thinning the orbital roof, and opening the Sylvian fissure and basal cisterns are the hallmarks of this approach.

see Anterior clinoidectomy

Drilling the anterior clinoid process, either extradurally or intradurally exposes the clinoidal or anteromedial triangle area. It is bordered by the optic nerve medially, oculomotor nerve laterally, and the tentorial edge extending between the second and third cranial nerves at the base. Watanabe, et al. found that the average measurements of the medial border, lateral border, base, and the area are 9.5, 13.3, 7.2 mm and 32.3 mm2, respectively 1)

Watanabe A, Nagaseki Y, Ohkubo S, Ohhashi Y, Horikoshi T, Nishigaya K, Nukui H. Anatomical variations of the ten triangles around the cavernous sinus. Clin Anat. 2003 Jan;16(1):9-14. doi: 10.1002/ca.10072. PMID: 12486732.
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