Intracranial Segment

Cavernous Segment

3.1Anatomic Layout

Above the petrolingual ligament, the internal carotid artery (ICA) can be considered to be intracavernous. From an endoscopic anterior viewpoint, we can define a paraclival and a parasellar segment, especially evident in well-pneumatised sphenoid sinuses. The paraclival segment corresponds to the vertical segment of the ICAc (cavernous portion of the ICA). Endoscopically speaking, this portion of the vessel represents the lateral border of the clival window. Although some authors have divided the paraclival portion in subsegments (Herzallah and Casiano 2007), we do not consider this further classification as having surgical utility. At a variable distance from the posterior clinoid process, the vertical segment— paraclival—bends forward, forming the posterior bend of the ICAc. Then, the artery usually runs horizontally for a short distance (horizontal segment) and curves upward, thus giving the anterior bend that reaches the anterior clinoid process. For this reason, the cavernous portion in the typical neurosurgical literature has been divided into five segments: posterior vertical, posterior bend, horizontal, anterior bend, and anterior vertical

(Inoue et al. 1990). It must be underlined that the configuration of the posterior bend varies significantly, and that sometimes it can bulge upward into and deform the dura of the cavernous sinus (CS) roof just lateral to the posterior clinoid process. The last segment, the anterior vertical,

also named the clinoid, infraclinoid or paraclinoid, is not completely intracavernous, but in “endoscopic” practice, it can be considered so; for this reason, we have included it in this section.

Different authors have tried to classify the ICAc, using different names but with similar conclusions (Herzallah and Casiano 2007; Jittapiromsak et al. 2010). These works both described two types of intracavernous ICA. Notwithstanding this, such differentiation appears of limited utility from an endosurgical viewpoint. Looking through a sphenoidal window, the parasellar ICA is positioned on the side of the pituitary gland, thus producing the parasellar ICA prominence on the sphenoid sinus wall. This prominence corresponds, more or less, to the distal part of the horizontal segment, the anterior bend, and the clinoid segment. The intracavernous segment of the ICA presents different branches, the most constant are the meningohypophyseal and the inferolateral trunk (ILT).

3.1.1Gross Anatomy

This portion grossly corresponds to the sphenoid sinus. Endoscopic anatomical landmarks are identified once a wide sphenoidal window is performed: the lateral and medial opticocarotid recess (lOCR and mOCR, respectively), the parasellar and paraclival carotid canal, the sellar prominence, the clival recess, and the strut of bone over the interCS. The lOCR is given by the pneumatisation of the optic strut, thus forming a recess that extends between the optic nerve superiorly and