Morphometry of the pterional and pterional-orbitozygomatic approaches to the basilar artery bifurcation by the use of neuronavigation systems: a new technical concept.

Much attention has been paid in the neurosurgical literature to optimising the approaches to intracranial pathology. The aims of the innovations reported are to increase the safety of operations by reduction of brain retraction and to improve exposure of the neurovascular structure in the operating area. It was our intention to investigate whether an image-guided frameless stereotactic system is suitable in morphometric studies based on the analysis of the pterional and the cranio-orbitozygomatic approaches to the basilar artery bifurcation (BAB). We analysed 60 virtual models of pterional craniotomy and the same number of those extended by orbitozygomatic osteotomy, created using computer tomography in the neuronavigation system. It was decided to calculate the percentage change of the cranial area of exposure, the depth of the surgical corridor and the angle of view to the bifurcation of the basilar artery. Three positions of the BAB (normal, high and low) were examined for each model of craniotomy. In the material analysed, after the extension of the pterional craniotomy by orbitozygomatic osteotomy, the cranial area of exposure for 60 models of cranio-orbitozygomatic craniotomies increased by a mean of 39.28% (from 30.89% to 48.06%). The decrease in the depth of the surgical corridor for a normal-lying BAB was 19.16%, for a high-lying BAB 19.09% and for a low-lying BAB 19.12%. The mean changes in the individual BAB locations did not differ significantly in statistical terms (F = 0.011; p = 0.99). The mean increase in the cranial angle of attack for a normally located BAB was 10.72 degrees , for a high-lying BAB 11.1 degrees and for a low-lying BAB 10.31 degrees . The post-hoc test showed significant differences in the angle of attack between a normal and a low-lying BAB (p = 0.034) and a high and a low-lying BAB (p = 0.00007). Neuronavigation systems, already well-known for their intraoperative use, can also be useful in morphometric studies, and the advantages of this method are the practically unlimited number of results which can be analysed in detail and the repeatability of the technique. The pterional-orbitozygomatic approach compared to the pterional increases the working area, minimises retraction of the brain, shortens the working distance, enables instruments to be used more easily, widens the angle of view and improves the visibility of the anatomical structures in the working area, especially for a high-lying BAB.