Introduction: Both the pterional and supraorbital approaches are standard techniques utilized by neurosurgeons on a daily basis to tackle multiple pathologies. Both approaches have been proposed as optimal access corridors to deep and paramedian anatomy purporting superiority in instrument maneuverability. Various studies have attempted to elucidate this question specific to intracranial structures. The present method used to assess surgical freedom is conceptually, procedurally and mathematically flawed, while also only taking into account the two-dimensional region produced by the surgical corridor. This study aimed to comprehensively assess key intracranial structures accessed via the surgical approaches using the volume of surgical freedom (VOSF) methodology.
Methods: Twelve cadaveric dissections (6 standard pterional transsylvian and 6 supraorbital craniotomies) were completed. Data points (three-dimensional Cartesian coordinates) with respect to predetermined neuroanatomy were collected using a neuronavigation system. The study was corrected for inter and intra-rater variability. The novel method developed in this laboratory was used to calculate the VOSF specific to critical intracranial anatomy for which these approaches are commonly used. Comparative analysis of the VOSF of the ipsilateral paraclinoid internal carotid artery, A1/M1 bifurcation and the anterior communicating artery complex was completed. The mean VOSF of all structures explicit to the surgical corridor was established and the sample t-test used to compare approaches.
Results: Via the supraorbital craniotomy, the mean accessible length of the ipsilateral A2 was 5.86 mm, resulting in a VOSF of 16.37 mm3 at most distal point on the vessel. Specific to the pterional transsylvian approach, the VOSF of the origin of the ipsilateral posterior communicating artery and tuberculum sellae were 33.38 and 35.02 mm3, respectively. The mean VOSF for the ipsilateral paraclinoid internal carotid artery, A1/M1 bifurcation, and anterior communicating artery complex when approached via a supraorbital craniotomy were 17.81, 16.35, and 15.63 mm3. The mean VOSF for the ipsilateral paraclinoid internal carotid artery, A1/M1 bifurcation, and anterior communicating artery complex when approached via a pterional craniotomy were 61.85, 61.23, and 34.29 mm3. When comparing the pterional and supraorbital craniotomies for all three structures, these results reached statistical significance with p-values of <0.001(paraclinoid internal carotid artery), <0.001(A1/M1 bifurcation), and 0.002 (anterior communicating artery complex).
Conclusion: When seeking to achieve maximal access to the ipsilateral paraclinoid internal carotid artery, A1/M1 bifurcation, or anterior communicating artery complex, the above statistically significant results affirm that the standard transsylvian pterional craniotomy provides the maximal VOSF and greatest instrument maneuverability. This comparison also suggests that a pterional approach produces a larger access corridor and thereby decreases the risk of potential surgical injury. This methodology can also generate spatially accurate three-dimensional models of instrumental freedom specific to the approach using a standardized unit of measurement, while depicting the maximal limitations of the corridor, regardless of irregular boundaries. This comparative study not only confirms the robust and advantageous qualities of this anatomical metric, but also translates quantitative anatomy into a surgical planning tool that can be used to maximize preoperative and intraoperative risk assessment.
