Background The transverse process of the atlas (TP-C1) has been identified as an important landmark
in several surgical approaches to the posterolateral skull base, but its anatomical
relationships have not been systematically described. Its key role in this region
stems from its shared developmental anatomy with the skull base, and from its proximity
to major neurovascular structures. In this study, we develop a comprehensive scheme
for understanding the complex region surrounding the transverse process.
Methods Six cadaveric heads (12 sides) were dissected to expose the transverse process and
its anatomical relationships from the lateral and posterolateral perspectives. We
examined the related muscles, bony landmarks, neurovascular elements, and previously
described surgical triangles. Measurements of the distance from the transverse process
to several important structures were made. Our findings were analyzed in the context
of the existing anatomical, surgical, and developmental literature.
Results From both a surgical and an artistic perspective, the TP-C1 lies at an anatomical
focal point toward which many of the posterolateral skull base structures converge.
Based on this observation, we devised a framework for understanding this region that
partitions it into angles defined by anatomical structures, all centered at the transverse
process. Together, these angles can be visualized as pieces of a pie. Muscles, such
as the superior and inferior oblique, as well as imaginary lines such as the “transverse-asterion”
line are used to define these angles. The transverse-asterion line also roughly divides
the posterolateral region into four major surgical quadrants: the transmastoid presigmoid
superolaterally, the suboccipital retrosigmoid superoposteriorly, the jugular foramen
inferolaterally, and the far lateral approach inferoposteriorly. Knowledge of the
typical distance of the transverse process from other important structures such the
spinal accessory nerve, facial nerve, and vertebral artery can also be helpful when
exposing this area.
Conclusion Even though the transverse process is an extremely useful landmark for posterior
and lateral skull base approaches, its anatomical relationships are sometimes overlooked.
From a surgical perspective, it is clear that the transverse process should be treated
as a crucial part of skull base anatomy. Similar to the triangles of the cavernous
sinus, the scheme we have described should facilitate such an understanding.
