The skull appears as an oblong convex shape. Within this shape it is made up of five surfaces which are the forehead, top of the head, back of the head and the two sides. What really separates these surfaces are the long paired bony temporal lines that run from the side of the brow bone in front to the base of the skull behind the ear. It is a long curved raised bony line that has a 180 degree arc along its course.
The temporal line of the skull is more than just a coincidental bony finding. It represents the attachment of the temporalis muscle which, like all muscle attachments, creates greater bone deposition due to the stress from muscle contraction. It is the broad attachment of the origin of the temporalis muscle which narrows down inferiorly to pass under the zygomatic arch to insert onto the coronoid process of the lower jaw.
When it comes to aesthetic skull reshaping surgery the bony temporal line is the demarcation between the sides of the head which are made up of soft tissue and the pure bony surfaces of the skull that lie between them. This has major impact on how the skull surfaces can and should be aesthetically changed. The forehead, top and back of the head can be reduced by burring of the bone or augmented by placing synthetic materials on top of the bone. On the sides of the head reductions have to be done by muscle removal and augmentations have to be done by placing implants on top of the muscle or fascia. That makes for a major difference in how these different surfaces of the head can be treated.
This head surface concept is important as many skull shape manipulations involve more than just one surface. This is particularly relevant in skull augmentations. Since the skull is a series of connected convex surfaces augmentations cover a lot more surface area than is often realized to blend in and look natural. As a result most skull augmentations cover or encroach on at least three surfaces. The back of the head skull augmentation, for example, covers the bak and wraps around a bit onto the sides and sometimes the top of the head. Most forehead augmentations does the same blending into the sides and top of the head. Since the sides of the head are soft tissue the augmentation must sit on top of the muscle and not done on the bone. This is why custom solid silicone skull implants are so effective as they can cover any type of skull surface. Bone cements in contrast must stay on bone and thus are much more limited in their skull augmentation capability.
A significant violation of this concept is when custom skull implants are made in which the surgeon believes that the implant must sit entirely on bone and needs to cross the temporal line to create its augmentation effects. Stripping off the muscle from the temporal line to place an implant creates a significant aesthetic problem after surgery as the released muscle contracts and creates a prominent bulge. Releasing and resuspending the temporalis muscle never works as the muscle merely contracts inferiorly. It is important to never strip off the muscle or fascia from the bony temporal line.
Dr. Barry Eppley
Indianapolis, Indiana