Geometric relationships of neural and bony landmarks of the cranial base

The skull base serves as structural support for the brain and as a conduit for neurovasculature. Traditional morphometric methods have intrinsic limitations which make wholistic assessment of this anatomy challenging. Here we applied geometric morphometric techniques to address the problems associated with traditional morphometric strategies for evaluating skeletal and soft tissue components of the skull base. A Microscribe® i+ 3-D digitizer was used to register the location of 20 3-D skeletal and neural landmarks on the skull base of 80 anatomic body donors (mean age 83.0 ± 10.1 years). Linear measurements of neurocranial dimensions were collected with traditional methods. A principal component analysis (PCA) was applied to Procrustes aligned coordinates of the 3-D data. The first principal component accounted for 34.24% of the variation and was associated with changes in clival width and sella turcica length. Shape changes associated with PC1 scores correlated with configuration size (centroid size) (R² = .532, p < .001). PC2 (12.85%) was associated with isolated changes in clival width driven by the jugular tubercles. Results related to PC3 (11.10%) showed variation in skull base flattening. PC2 and PC3 results were correlated with neurocranial length and measurements of cranial width. Skull base size emerged as a principal driver of skull base shape. The jugular tubercle and surrounding foramina represented another locale of variation. Finally, our results support the idea that a wide range of non-pathologic skull base flattening may exist, as this shape axis was a major contributor to the variation seen in the sample.