VCOM Research Day Program Book 2023

Medical Student Research Biomedical

10 Geometry of Cranial Nerve Egression in the Posterior Cranial Fossa with Considerations for Neurosurgical Approaches

Alexandra Luna; Kaivon Kouhestani; Amanda Swaak; Chelsea Bengson; Benjamin Mann; Jonathan Millard Corresponding author:

Edward Via College of Osteopathic Medicine-Virginia Campus

While osteological knowledge of the human cranial skeleton overall is immense, the information surrounding the geometric diversity of cranial nerve positioning relative to bony landmarks is limited. This information is relevant for minimizing soft tissue damage during surgical resections that involve navigating around cranial nerves such as clival chordoma excisions. It can also improve the safety of surgical approaches to the jugular foramen. Here we describe the three-dimensional relationship of the abducens nerve (CN VI), glossopharyngeal nerve (CN IX), vagus nerve (CN X), and hypoglossal nerve (CN XII) with surrounding bony landmarks. Standard dissection techniques were used to reveal the floor of the cranial cavity on 34 formalin-fixed whole-body donors (mean age 84 years; 21 female and 13 male). Pseduo-bi-pterion and pseudo-bi-asterion cranial width measurements were recorded with digital calipers. AMicroscribe ® i+ 3D Digitizer portable coordinate measuring machine was used to record the position of seven 3-D landmarks. Landmarks included three bony landmarks (planum sphenoidum, dorsum sella, and jugular tubercles) and four dural meatuses

marking the penetration of CN VI, CN IX, CN X, and CN XII. MorphoJ v1.07a and PAST v4.11 were used to apply geometric morphometric techniques and statistical tests. Procrustes superimposition was applied to the raw landmark coordinates to isolate shape conformation and remove the effects of morphospace location and scale. Principal component analysis (PCA) was used to explore shape conformations which have the greatest contribution to the overall variation of the configuration. Independent samples t-tests were used to test differences between male and female principal component (PC) scores, and the relationship of PC scores to cranial width were explored. Results were visualized using lollipop graphs and wireframe diagrams, while 3DSlicer v5.2.1 and Landmark Editor v3.6 were used to enhance 3-D visualization. The PCA revealed five loadings capturing 78.834% of total shape variation. The first principal component (PC1) captured 29.026% of the shape variation and demonstrates medial-lateral movement of all clival features with superior-inferior movement of the two midline features; PC2 accounted for 20.966% of the shape variation and showed

medial-lateral movement of skeletal features of the clivus with extreme displacement of the abducens nerve. Males and females were significantly different along PC2 (at α =0.1) ( t (28)=2.0, p =0.55). Cranial width index has a moderate positive correlation with PC2 scores ( r (28)=.431, p =.02). Our data supports the concept that female individuals may be at greater risk of abducens nerve injury during approaches to the posterior cranial fossa because of CN VI displacement toward the jugular tubercle and jugular foramen. In contrast, Male CN VI morphology tends to stay more superior, located on the clivus near the spheno occipital junction. PC2 scores tend to increase with cranial width index. Future directions should further explore the relationship of group membership with posterior cranial fossa morphology as it may inform safer surgical approaches.


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