Speculum opening in transsphenoidal surgery.

OBJECTIVE

To assess the extent to which the transsphenoidal speculum can be safely opened at the face of and within the sphenoid sinus without risking damage to the optic nerves in the optic canals and at the orbital apex and the nerves coursing adjacent the walls of the sphenoid sinus.

METHODS

The distance was measured between the optic nerves at the level of the anterior wall of the sphenoid sinus and 0.5 and 1.0 cm within the sinus. In addition, the distance between the middle turbinates and the contralateral optic canals was assessed because this turbinate is the largest structure blocking access to the sphenoid sinus in the transsphenoidal approach and tends to force the speculum away from the midline and toward the optic nerve in the contralateral side of the approach.

RESULTS

Opening the transsphenoidal speculum at the anterior wall of the sphenoid sinus beyond 2.5 centimeters carries some risk of damaging the optic nerves and this distance narrows when the speculum opening is positioned inside the sphenoid sinus. Displacement of the speculum to one side by the middle turbinate places the speculum near the contralateral optic nerve and may be associated with optic nerve injury with lesser degrees of speculum opening.

CONCLUSIONS

Careful attention should be directed to avoiding excessive opening of the transsphenoidal speculum at the anterior face of the sphenoid or within the sphenoid sinus.