The Vectorial Technique: A New Tool to Measure Angles of Exposure in Skull Base Anatomical Dissection

Background: Anatomical dissections play a role of paramount importance in the understanding and development of complex surgical approaches in skull base surgery. To accomplish this task, objective measurement techniques are needed.

Objective: To describe a neuronavigation-based technique able to objectively measure angles of exposure of circular bony structures such as the skull base foramina.

Methods: The technique uses Cartesian coordinates collected from the rim of specific circular targets through a neuronavigation system and a vectorial formula to measure the arches of exposure and the relative angles of exposure. To test its reliability, a validation experiment was performed by comparing measurements obtained both through the new technique and a standard goniometer from the rim of a circular bucket, which was CT-scanned, fixed, and registered for neuronavigation. Subsequently, the technique was applied to two different cadaveric experiments. First, the angles of exposure of the hypoglossal canal exposed using a far-lateral, far-medial, and transoral approach were measured in three cadaveric specimens. Second, the angles of exposure of the petrosal apex were obtained and measured after performing a contralateral endoscopic endonasal, a contralateral trans-maxillary, and a contralateral trans-facial approach in three cadaveric specimens.

Results: The validation test confirmed the comparability of the two methods employed and therefore its reliability. In the cadaveric setting, the far-lateral granted a mean angle of exposure of 243 degrees dorsally, the far-medial of 129 degrees, and the transoral of 94 degrees, both ventrally. In the second experiment, the endoscopic endonasal approach offered an angle of exposure of the petrosal apex of 24 degrees, the contralateral transmaxillary of 53 degrees, and the contralateral transfacial of 83 degrees.

Conclusion: To the best of our knowledge, this is the first method that allows the quantification of angles of exposure of circular targets, exposed through different surgical routes.

Publication History

Article published online:
01 February 2023