Meningo-orbital fold (MOF) as a guiding point in extradural approach to the anterior clinoid process

BACKGROUND AND PURPOSE: The essential stage of Dolenc's approach to the cavernous sinus is the incision of the meningo-orbital fold (MOF) without damaging nervous structures in the superior orbital fissure. The goal of the research is to perform a topographic and morphometric study of the meningo-orbital fold. MATERIAL AND METHODS: Formalin preserved central cranial base specimens from twenty adults (40 sides) were dissected for this study. The dissection was based on Dolenc's epidural approach to the cavernous sinus. RESULTS: The average width of MOF is 8.4 mm on the right side and 8.3 mm on the left side. The meningo-orbital artery (MOA) is an important reference point in recognizing the superior orbital fissure. In 75% (15 specimens) of cases the meningo-orbital artery passes by the superior fissure at a distance of a few millimeters. In 25% (5 specimens) of cases the MOA passes through the lateral margin of the superior orbital fissure. CONCLUSIONS: The MOF is an inset of the external layer of the dura mater of the middle cranial fossa which passes through the superior orbital fissure and joins the periorbita at the level of the sphenoparietal sinus. The average width of the MOF is 8.4 mm on the right side and 8.3 mm on the left side. The new approach to the safe incision of the MOF relies on the medial margin identification by splitting both layers in the lateral wall of the cavernous sinus between V1 and V2. After identification of the medial margin, it is possible to separate the margin from the superficial layer of the cavernous sinus, from the side anterior and middle cranial fossae. It is then possible to perform a safe incision of the MOF without any danger of damaging the nerves.