Anatomical study of the superior orbital fissure as seen during a pterional approach.

OBJECT The superior orbital fissure (SOF) is an important landmark in the neurosurgical pterional approach, but the anatomical features of the SOF and the procedures necessary to fully expose it and its contents have not been detailed. Although the pterional approach is commonly used during skull base or vascular surgery by neurosurgeons who may already be familiar with its nuances and anatomical relationships to the SOF, this knowledge may also be useful to the wider neurosurgical community. The authors describe the spatial relationships of the contents of the SOF and suggest a specific sequence of steps for exposing the SOF region in a pterional approach. METHODS Using standard microsurgical equipment and instruments, the authors performed 20 pterional approaches in 10 embalmed cadaver heads in which the vascular systems had been injected with colored material. Five sequential steps were delineated for approaching and dissecting the SOF and its contents: (1) drilling the sphenoidal ridge, anterior clinoidal process, and part of the greater and lesser wings of the sphenoid; (2) resecting the dural bridge; (3) detaching the hemispheric dura mater, thereby exposing the anterior portion of the cavernous sinus and the neural component entering the SOF; (4) identifying and dissecting the extraanular structures; and (5) opening the anulus of Zinn and identifying its neural constituents. CONCLUSIONS Knowing the 3D relationships of the contents of the SOF encountered in the pterional approach enables safe neurosurgical access to the area. The proposed sequence of steps allows a controlled exposure of the SOF and surrounding areas. Untethering the frontotemporal lobe by transecting the dural bridge connecting the dura to the periorbita allows good exposure of the basal frontotemporal lobes, both intra- and extradurally, and reduces brain retraction.