Anatomic Basis of Endoscopic Skull Base Surgery and Clinical Implications in 277 Approaches: Part 2 beyond the Sella—from Cribriform Plate to Craniovertebral Junction

The purposes of this article are to review the surgical neuroanatomy of the skull base through an endoscopic transnasal route with image guidance, and to present our clinical experience in 277 approaches on skull base endoscopy over the last 4 years. Ten modifications of the endoscopic transnasal approaches were performed; they were: transmaxillary, transpterygoid, transplanum, approaches above and below the pituitary gland to the perimesencephalic cisterns, transventricular approaches, transclival approach, and approaches to the craniocervical junction (CCJ) and the orbit. A Stryker Image Guidance System was used to delineate the limitations of each approach. The transmaxillary approach exposed pterygopalatine fossa, the transpterygoid approach revealed the foramen ovale and the petrous apex region, and the transplanum approach exposed the structures within the chiasmatic and lamina terminalis cisterns and the interhemispheric fissure. The approach above the pituitary gland exposed the chiasmatic and carotid cisterns, and the approach below the pituitary gland exposed the interpeduncular and prepontine cisterns. The transventricular approach via the tuber cinereum and lamina terminalis exposed the third ventricle. The transclival approach exposed the interpeduncular, prepontine, cerebellopontine, premedullary, and cerebellomedullary cisterns. The approach to the CCJ exposed the premedullary and anterior spinal cisterns, and the transethmoidal approach to the orbit exposed the intraorbital contents through a working space between the inferior and medial rectus muscles. Of the 277 approaches, 9% (20 cases) were for primary CSF fistulas, 5% (13 cases) for clival chordomas, and 3% (7 cases) for odontoid resections. Detailed knowledge of endoscopic anatomy of the anterior skull base is a prerequisite for a safe and effective surgery during extended approaches.