Removal of the Posterior Wall of the Sphenoid Sinus During Trans-sellar Skull Base Surgery: The Meniscus Sign

Introduction: With the goal of maximizing surgical exposure for the intradural portion while minimizing surgical complications during transsellar surgical approaches, bone removal from the sellar dura is sometimes suboptimal. Tumors can distort the appearance of the posterior wall of the sphenoid sinus, and a surgeon’s concerns for avoiding the proximal vascular structures of the region may compromise access for the neurosurgical portion of the operation. Our method for removal of the posterior wall of the sphenoid sinus is a reliable and easily taught technique that promotes safety while maximizing bone removal and surgical access between the cavernous sinuses and internal carotid arteries.

Methods: The inferior and middle turbinates are lateralized, and the ipsilateral septal flap is removed. The ipsilateral sphenoidotomy is performed, and the exposed septal cartilage/bone is removed. Leaving the contralateral septal flap intact, the contralateral sphenoidotomy is performed. Both sphenoidotomies are connected. The sphenoid rostrum is drilled, and the “inferior triangles,” which bound the rostrum laterally and point toward the clivus inferiorly, are drilled. The meniscus sign is observed when the posterior wall of the sphenoid sinus is removed. A diamond bur is used to thin the posterior wall bone until a curette can be introduced for removal of bone overlying the dura/pituitary capsule. The wide removal of bone for appropriate surgical access brings the surgeon’s instruments in close proximity to the cavernous sinus and internal carotid artery. When the posterior wall is transgressed, a small amount of blood or irrigation fluid will collect in the potential space that develops behind the posterior sphenoid wall and the sellar dura. Pressing on the dura with a blunt instrument demonstrates the extent to which sellar bone can be safely removed. With pressure, the blood and fluid in this potential space will clear, and the surgeon can remove all of the bone overlying this area of clearing. The surgeon repeatedly palpates the sellar dura and follows the meniscus sign, removing bone superiorly and laterally until pressure on the dura no longer results in clearing of the fluid from the potential space. This failure to clear the potential space indicates that surgical bone removal has reached the fixed dural reflections of the cavernous sinus.

Conclusion: The meniscus sign is a convenient and reliable method for safe removal of the posterior wall of the sphenoid sinus during transsellar skull base surgery. The potential space that fills with blood and irrigation fluid can be palpated and used as a guide for removal of sellar bone. Removal of only that bone overlying the clearing of the meniscus will prevent surgeons from entering areas of fixed dural reflections at the cavernous sinus and carotid artery. The senior author has employed the meniscus sign in transsellar surgery for more than 15 years, noting that the technique has been free of surgical complications, reproducible amongst residents and fellows, and reliable in safely providing maximum exposure for the intradural portion of the operation.