Flatness of the back of the head is the single most common patient concern when a skull shape deficiency exists. The flatness can be on one side or both or can be higher or lower but it is always about lack of enough prominence or projection on the back of the head.
In evaluating back of the head shape issues, it is important to understand the bony anatomy. While the back of the head is often referred to as the occiput, this is not an accurate descriptive term. The back of the head is actually formed by a combination of the occipital and paired parietal skull bones. These two bones interface along the lambdoidal suture line. What is relevant is that most of the visible back of the head is composed of the parietal bones not the occipital bone. The occipital bone only makes up the very bottom of the back of the head and is often not what makes it look flat or lacks projection. The occipital bone is more commonly at fault for aesthetic excesses which require reduction.
The flatness of the back of the head can be appreciated in 3D CT scans for custom skull implant designing. Almost everyone that I have seen with a flat back of the head concern has normal or near normal occipital bone projection. But beginning at the lambdoidal suture line the significant flatness begins which involves the parietal bone up to the top of the head at the end of the sagittal suture line. In compensatory fashion the top of the head may actually be higher than normal.
In designing custom skull implants for the back of the head the key issues are the location the maximum point of projection and the surface area coverage (footprint) of the implant. The maximum point of projection depends on the patient’s perception of the angulation of expansion needed. For most men this is going to be much more of a horizontal projection bringing it straight back or close to that direction. For most women however the maximum point of projection is often higher to establish increased crown height as well.
The other important design principle is adequate surface area coverage. One of the key principles in onlay skull implant designs is that the must be much bigger in surface area courage than one would think. To have a natural look that blends into the rest of the skull without visible transitions or abnormal looking shapes requires a large implant footprint. This means that when adding increased projection to the back of the head the implant must wrap around the sides and across the top as well. From a gestalt perspective the implant must look like it is a natural extension of the skull or to put it another way…it must look like it belongs there.
Dr. Barry Eppley