The Recesses of the Sellar Wall of the Sphenoid Sinus and Their Intracranial Relationships

Introduction: The sellar wall of the sphenoid sinus and its recesses have been previously studied, but their intracranial relationships to the clinoid segment of the internal carotid artery, chiasmatic sulcus, tuberculum, diaphragma sellae, and middle clinoid process need further definition.

Objective: The objective of this study is to describe the intra- and extracranial relationships of the recesses in the anterior sellar wall.

Methods: The middle clinoid was studied in 132 parasellar areas of dry skulls. Thirty-eight parasellar areas of formalin-fixed/silicone-colored specimens were dissected. After transsphenoidal endoscopic exposure, the optic, carotid, and sellar prominences; lateral opticocarotid and tuberculum recesses; caroticosellar and medial opticocarotid points were identified. High-speed drills opened 1-mm perforations at the reference points to allow study of intracranial relationships.

Results: Two recesses and two junction points can be recognized in the sellar wall of the sphenoid sinus in most cases: the lateral opticocarotid, and tuberculum recesses; the medial opticocarotid, and caroticosellar points. The lateral opticocarotid recess corresponds and often extends into the optic strut, and its medial projection is related to the clinoid segment of the internal carotid artery. The level of the lateral aspect of the distal dural ring, formed by the dura extending medially from the upper surface of the anterior clinoid process around the carotid artery, is 1.15 mm superior to the tuberculum recess. The deepest part of the tuberculum recess corresponds in 50% of sphenoid sinuses to the tuberculum sellae, with the remainder being located within a 2.5-mm range above or below the tuberculum recess. The diaphragma sellae attachment is located at the level of the tuberculum recess or slightly inferior. When a carotid cave is present, it can be referenced medial to the carotid artery between the medial opticocarotid and caroticosellar points. No sinus prominence or recess corresponds to the chiasmatic sulcus as the surface of the planum blends into the tuberculum recess. The chiasmatic sulcus can be referenced in the sphenoid sinus in the area above the tuberculum recess between both optic prominences. A clinically relevant middle clinoid process (greater than 1.5 mm) is present in 21.1% of parasellar areas and joins the anterior clinoid forming a caroticoclinoid ring in 2.94%. The superomedial point of the middle clinoid process base is most frequently located approximately 1 mm inferior and lateral to the caroticosellar point, with its highest part further inferior and lateral. The middle clinoid is inferior to the medial opticocarotid point in all cases, 4.75 mm on average. The middle clinoid process protrudes inside the cavernous sinus; in case of a caroticoclinoid ring, this structure forms part of the roof of the cavernous sinus.

Conclusion: An understanding of the intra- and extracranial relationships of the recesses of the sphenoid sinus will aid in accurately directing transsphenoidal approaches.