Orbital Venous Drainage into the Anterior Cavernous Sinus Space; Microanatomic Relationships

Abstract

Microsurgical anatomy and relationships in the region of the superior orbital fissure and anterior part of the cavernous sinus were studied, with special attention to the venous structures. Microanatomic dissections were performed in 24 specimens from human cadavers, fixed in formalin, with the aid of a microdrill and operating microscope. A protocol of dissection was developed, enabling plane-by-plane exposure of the cranial nerves passing from the cavernous sinus to the superior orbital fissure and farther, on disclosure of the junction between the ophthalmic veins and the anterior cavernous sinus space. The main draining vessel was the superior ophthalmic vein. The inferior ophthalmic vein was much thinner and it was identified in 91.7% of cases. These two vessels fused together to form a common venous confluence approximately 5 mm in length that entered the anterior cavernous sinus space in its anterior or anteroinferior aspect. The shape of this venous drain varied greatly, from that of a typical vein to that of a venous lake. The latter was characterized by a relatively narrow opening into the anterior cavernous sinus space and lacunar widening of the vessel in its central part. No case of a separate entrance of the superior and inferior ophthalmic veins into the anterior cavernous sinus space was encountered. The anterior cavernous sinus space was described as a slit-like venous chamber located in front of the anterior genu of the intracavernous segment of the internal carotid artery. The anteroposterior diameter of this space was 3.2 +/- 0.4 mm; it was filled with blood, and no venous structures inside this space were observed. The knowledge of the anatomic details described may be useful for elaborating surgical approaches to this region and for planning the treatment of carotid-cavernous fistulas.