Meningeal layers around anterior clinoid process as a delicate area in extradural anterior clinoidectomy : anatomical and clinical study

Abstract

Objective: Removal of the anterior clinoid process (ACP) is an essential process in the surgery of giant or complex aneurysms located near the proximal internal carotid artery or the distal basilar artery. An extradural clinoidectomy must be performed within the limits of the meningeal layers surrounding the ACP to prevent morbid complications. To identify the safest method of extradural exposure of the ACP, anatomical studies were done on cadaver heads.

Methods: Anatomical dissections for extradural exposure of the ACP were performed on both sides of seven cadavers. Before dividing the frontotemporal dural fold (FTDF), we measured its length from the superomedial apex attached to the periorbita to the posterolateral apex which connects to the anterosuperior end of the cavernous sinus.

Results: The average length of the FTDF on cadaver dissections was 7 mm on the right side and 7.14 mm on the left side. Cranial nerves were usually exposed when cutting FTDF more than 7 mm of the FTDF.

Conclusion: The most delicate area in an extradural anterior clinoidectomy is the junction of the FTDF and the anterior triangular apex of the cavernous sinus. The FTDF must be cut from the anterior side of the triangle at the periorbital side rather than from the dural side. The length of the FTDF incision must not exceed 7 mm to avoid cranial nerve injury.

Keywords: Anatomical study; Extradural clinoidectomy; Frontotemporal dural fold; Superior orbital fissure.

Fig. 1

Surgical anatomy of the right anterior clinoid process and surrounding neurovascular structures. SOFh : horizontal limb of the superior orbital fissure, SOFv : vertical limb of the superior orbital fissure, V2 : maxillary branch of the trigeminal nerve, FTDF : frontotemporal dural fold.

Fig. 2

To avoid injuring the cranial nerves, the horizontal meningeal limb of the superior orbital fissure must be cut in a direction parallel to the anterior clinoid process, not perpendicular to it, and from the anterior side of the triangle at the periorbital side rather than from the dural side. FTDF : frontotemporal dural fold, V2 : maxillary branch of trigeminal nerve.

Fig. 3

Photographs showing the posterior view of the superior orbital fissure. The vertical neural limb (SOFv) and horizontal meningeal limb of the superior orbital fissure (SOFh) are schematically demonstrated.

Fig. 4

Photographs showing the relationship between the superior orbital fissure and neural structures on surgical position. The III, IV, V1 and V2 cranial nerves pass through the vertical neural limb of the superior orbital fissure (ellipse). The frontotemporal dural fold (FTDF) is within the horizontal meningeal limb of the superior orbital fissure (full line). The actual measurements are visible.