Clinoid

Clinoid refers to structures associated with the clinoid processes of the sphenoid bone, a group of bony projections that form part of the anterior boundary of the middle cranial fossa and contribute to the roof and walls surrounding the optic canal and sellar region. The term typically encompasses the anterior clinoid process, the middle clinoid process, and the posterior clinoid process. These processes help define the clinoid region, which is an important reference point in skull base anatomy and neurosurgical approaches.

The anterior clinoid process projects from the medial end of the sphenoid’s lesser wing near the optic canal. It forms part of the roof of the optic canal and contributes to the boundary of the superior orbital fissure. The middle clinoid process is a smaller projection on the sphenoid body between the tuberculum sellae and the dorsum sellae; its presence is variable, and it can be reduced, absent, or fused with adjacent structures. The posterior clinoid process projects from the dorsum sellae and forms the posterior boundary of the clinoid region, contributing to the posterior aspect of the sellar area near the cavernous sinus.

Clinical relevance centers on skull base surgery and vascular-neural relationships in the parasellar region. Removal of the anterior clinoid process, known as clinoidectomy, is performed to gain access to the parasellar region, sellar lesions, or aneurysms of the intracavernous or supraclinoid internal carotid artery. Variations such as a carotico-clinoid foramen—where the clinoid process fuses with the carotid canal—alter the local anatomy and imaging interpretation.

Imaging of the clinoid region relies on CT for detailed bony anatomy and MRI for surrounding neurovascular structures. A clear understanding of clinoid anatomy and its variants is essential for planning neurosurgical approaches and interpreting skull base imaging.