Endoscopic endonasal skull base surgery: Part 3--The clivus and posterior fossa.

OBJECT: As a minimally invasive surgical strategy, endonasal endoscopy has been implemented for the surgical treatment of clival and midline posterior fossa lesions which conventionally require radical and extensive surgical exposures. A cadaver study was performed and, subsequently, this technique was adopted into patient treatment.
METHODS: Six cadaver head specimens were used in this study. Anterior sphenoidotomy was attained by either a paraseptal or middle turbinectomy approach. The ideal head positioning was measured. The clival bone was removed with a high-speed drill from sella to foramen magnum in the vertical dimension and from carotid artery to carotid artery in the transverse dimension. The width of the clival bony window between the carotid arteries was measured at the level of the sellar floor and the caudal end of the carotid artery. The surgical anatomy was studied.
RESULTS: Although the middle turbinectomy approach provided a wider surgical corridor, exposure with the paraseptal approach was sufficiently ample. Ideal head positioning was at 15-degree flexion of the forehead-chin line. The average width between carotid arteries at the sellar floor level was 16 mm (range 12-22 mm) and at the lower end of the carotid arteries it was 19 mm (range 14-23 mm). When the dura mater was opened, the anterior view of the pons and medulla with corresponding cranial nerves and vasculature was encountered. Four illustrative patient cases are presented.
CONCLUSIONS: This endonasal endoscopy provided excellent surgical exposure from the sella to the foramen magnum at the midline clivus and posterior fossa. Surgical techniques and illustrations of four patients are presented.