Background: Total skull augmentation, or enlargement of the entire head, is an uncommon procedure amongst all types of skull reshaping procedures. Almost always expanding the outer surface of the skull in a near 180 degree manner requires a first stage scalp expansion procedure to ensure a competent scalp incision closure. A prior skull augmentation procedure may suffice in some cases depending upon what amount of material and its location are located.
Historically I have done total skull enlargement with a PMMA bone cement material with a first stage scalp expander phase. (hydroxyapatite cements are silly too expensive to use for most patients) This has been successful in most cases using material volumes in the 180 gram to 240 gram range. While effective it requires a lot of intraoperative material shaping and layering applications. It is also prone to some material irregularities and edging issues.
Today large skull enlargement procedures use a custom implant approach. It offers the creation of a controlled implant design that uses the prior augmentation material, if present, in how to create an improved implant shape. Its design is always done in two pieces which is necessary from a both manufacturing and surgical placement standpoint.
Case Study: This middle-aged male had a prior two stage skull augmentation procedure five years previously using PMMA bone cement. He had a well healed result, nice skull shape that was smooth and a beautifully healed scalp scar. He decided that he wanted a larger skull augmentation that added additional height to the top as well as some increased width at the sides.
A custom implant approach was used in designing a larger skull implant to make the desired changes. The total implant volume was 320ccs compared to 240ccs from the prior augmentation, a 38% increase in total material volume
Under general anesthesia his original scalp incision, which was barely detectable, was reopened and the bone cement chiseled out. It was extremely adherent to the skull with a very thin capsule between it and the bone.A capsulectomy was performed on the skull bone and temporalis facia and capsular releases were done on the capsule on the deep scalp layer. The implant was inserted in a two piece fashion as per its design and initially reunited with large permanent sutures. It was then further secured with a staggered screw placement. The scalp was closed in two layers over it with some tension.
This secondary skull augmentation case illustrates the value of a 3D custom design approach using the indwelling implant material as a guide. It also ensures a smooth outer implant surface and feather edging all the way around its perimeter. A very relevant question is how much more augmentation can be obtained in a patient who has had a prior skull augmentation In this case an approximate one-third increase in volume was done but that resulted in a fairly tight scalp closure. As a general rule a 20% to 30% increase is what is a realistic and safe skull augmentation increase.
Case Highlights:
1) Total skull enlargement can be done using either bone cements or a custom implant.
2) Having a prior skull augmentation procedure, regardless of the material used, is needed for a larger secondary skull augmentation because it creates some scalp expansion.
3) A large custom skull implant replacement requites a two piece design approach to keep the scalp incision more limited.
Dr. Barry Eppley
Indianapolis, Indiana