Study on measurements for margin of safety in lateral operation of a transnasoethmoid-sphenoid approach to decompress the optic canal.

OBJECTIVE: The surgical approach through nasal and ethmoid cells to sphenoid sinus is a common clinical method to do the decompression of the optic canal. During this surgery, we can follow landmarks such as ethmoidal arteries. However, when we do the surgery, it is possible to open excessively in lateral operation and damage orbital medial wall. To prevent this from happening, we do a lot of measurements to estimate the distance in lateral operation. We hope to give surgeons some help in clinical use.

METHODS: We chose 120 brain imaging findings that showed a normal appearance in our measuring area by means of three-dimensional reconstruction based on high-resolution spiral computed tomography scans. We chose several anatomic landmarks and measured the distances in lateral operation and located a projection point for directing this surgery.

RESULTS: The mean values of distance from dacryon and the anterior foramen of the optic canal to the index plane were 5.439 ± 2.4496 and 9.334 ± 2.0628 mm. The mean values of distance from trisection points to the orbital medial wall were 7.359 ± 2.2262 and 6.911 ± 2.3102 mm. The mean value of distance from the projection point to the ipsilateral outer edge of the supraorbital notch was 30.379 ± 5.3676 mm. There are no significant differences for all the distance between the left side and right side. The median of right-side angle between the straight line connecting both sides of the outer edge of supraorbital notch and the straight line connecting the projection point with the ipsilateral outer edge of the supraorbital notch is larger than the left one and has a less variation than the left one.

CONCLUSIONS: The lateral distance in surgical operation is consistent among individuals, which can give a safe area to surgeons in lateral operation. The location of the projection point gives surgeons an indication of direction to this surgery.