114 - Geometric Morphometric Analysis of the Cranial Nerve-dural Interface in the Posterior Cranial Fossa

Poster Board Number: 114
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Abstract Body : Knowledge of skull base anatomy and its intimate association with neurovascular structures is important when considering safe neurosurgical approaches. While the relevant anatomy and its variants have been thoroughly discussed within the literature, there has been minimal research describing the relative geometric locations of the structures. The goal of this research is to explore 3-D geometric variability in skeletal and cranial nerve features of the posterior cranial fossa. Standard dissection techniques were used to reveal the posterior cranial fossa on 34 formalin-fixed whole-body donors (13 Male and 21 Female; mean age=84 years). A Microscribe® i+ 3D portable coordinate measuring machine was used to register the location of 20 3-D landmarks. Landmarks included three bony landmarks (planum sphenoidum, dorsum sella, and jugular tubercle), four dural meatuses marking the penetration of CN VI, CN IX, CN X, CN XII bilaterally, as well as four landmarks circumferentially outlining the internal acoustic meatus (IAM) bilaterally. Seven crania were remeasured by a second landmarker to assess protocol reliability. Data were analyzed with MorphoJ v1.07a. For the final analysis, 29 donors were retained after filtering for missing data and erroneous captures. Generalized Procrustes analysis was used to remove nuisance factors and isolate shape formation while principal component (PC) analysis was used to explore variability in landmark configurations. Lollipop and wireframe diagrams were used to interpret results. Independent samples t-tests were used to assess male and female group PC scores. 3Dslicer v5.0.3 and Landmark editor (IDAV) v3.0 were used to enhance visualization. PC analysis reported 27 principal components, with the first four PCs accounting for 74.063% of the overall variation in the shape. PC1 represents 34.573% of the total variance in the sample and demonstrates mediolateral displacement of internal acoustic meatus and jugular dural meati with notable anteroposterior concomitant displacements of CN VI, jugular tubercles, and CN XII. PC2 captures 17.713% of the variation in the sample shape. It is characterized by anteroposterior and mediolateral movement of midline skeletal features, including jugular tubercles with opposite mediolateral/superoinferior movement of the internal acoustic meatus. PC3 captures 12.808% of the variation in the shape. It is characterized by opposite anteroinferior movements of the planum and dorsum sella and sharp superoinferior movements of the CN VI dural meatus with mediolateral movement of the jugular tubercle. PC4 represents 8.968% of the variance in the sample and shows extensive mediolateral movement of all clival features with negligible changes in the IAM and jugular dural meati. Males and females were different along PC4 (at α=0.1) (p=.053). Procrustes ANOVA revealed the effect of individual variation to be 2.2 times greater than the effect of landmarker precision. These results highlight vertical variability in features along this clivus, both in tilt and coronal displacement. PC3 results demonstrate considerable variation in CN VI egression relative to other landmarks; PC4 is notable because it seems to highlight sexual dimorphic conformations, with female individuals having a more platybasic morphology. Future directions should include further investigation of group differences with special attention to characterizing landmarks salient for specific surgical approaches.