Lateral safety limits during a facial transclival approach to the craniovertebral junction

Transclival procedures are infrequently performed and carry some dangerous complications. The carotid arteries and the hypoglossal nerves are the most important structures at risk during the subperiostal lateral dissection of the posterior wall of the oropharynx. These lateral landmarks are, however, not easily identified during the surgical dissection.

We measured the location of the foramen lacerum externum and the hypoglossal canal with respect to the midline. These measurements were performed on 76 non-pathological CT-scanned skulls that were converted into accurate three-dimensional digital reconstruction models by the use of 3D image-processing. The same measurements were also taken on 15 non-pathological skulls by the use of a slide calliper.

For the foramen lacerum, the distance to the midline was 11 mm +/- 1 mm SD (range 8-14 mm) on the right-hand side and 11 mm +/- 1 mm SD (range 9-14 mm) on the left-hand side. For the right hypoglossal canal this distance was 17 mm +/- 1 mm SD (range 15-22 mm) and for the left hypoglossal canal 17 mm +/- 1 mm SD (range 14-20 mm). There was no significant difference between left and right.

The posterior wall of the oropharynx can be safely dissected for at least 8 mm from the midline at the level of the foramen lacerum and for at least 14 mm towards the hypoglossal canal from the midline at the level of the anterior border of the foramen magnum. In addition, this technique with the help of 3D software, can be very useful in the pre-operative setting when performing complex skull base procedures.