Paraclinoid aneurysms are frequently encountered at the carotid siphon. The clinoid segment of the internal carotid artery (ICA) is situated at the transition of the artery from the cavernous sinus to the subarachnoid space and has been poorly understood because the anatomy of this region is extremely complex and variable. Understanding the clinoidal segment is important for correctly diagnosing and managing these aneurysms because the risks of aneurysm rupture vary with the specific location of lesions along this small segment of the ICA. The site of origin, projection, and relationship of aneurysms arising from the ophthalmic segment of the ICA to adjacent structures are heterogeneous. The complex anatomy of the paraclinoid ICA makes the surgical management of aneurysms arising from this segment difficult. The main features of successful surgical treatment of these lesions include establishing control of the proximal artery, adequate exposure of the aneurysm neck, and successful obliteration of the aneurysm with minimal manipulation of the optic nerve. The carotid cave is a virtual space, immersed in a small segment of the ICA, the clinoid segment. The clinoid segment is situated inside the clinoid space. This short segment has been poorly understood and for this reason the nomenclature of aneurysms of this area is extremely confusing. This paper reviewed the microsurgical anatomy of the carotid cave, the paraclinoid region, the clinoid space, and the clinical significance of the anatomy in accord with aneurysm growth.