Background: Skull implant augmentation is unique in many ways that largely revolve around its overlying scalp coverage. Besides its visibility the most important feature of the scalp is its tight adherence to the skull. It is best thought of as skin stretched over a beach ball. The point being is that it is tight and this tightness has a major impact on any skull augmentation procedure. It will affect how much skull augmentation can be achieved.
The scalp does have some flexibility when detached from the bone which is influenced by its thickness. Thicker scalps are more elastic than thinner scalps. The thickness of the scalp is directly related to the patient’s ethnicity and skin pigmentation. The lighter the skin pigment and hair color the thinner the scalp usually is. Conversely the darker the skin pigment the thicker the scalp is. The thicker the scalp is the more flexibility it has and the greater skull augmentation effect that can be achieved by an implant pushing outward under it.
Another important variable that can affect scalp flexibility in potential skull augmentation patients is a history of hair transplantation. If a strip hair harvest has been previously done scalp flexibility will be decreased due to the lost scalp tissue. Any other excisional procedures (e.g., frontal hairline advancement) creates the same loss of scalp flexibility.
Assessing scalp flexibility in any skull implant procedure is important but is paramount in larger augmentation needs when the scalp flexibility is limited. This problem is circumvented by the use of a 1st stage scalp expander. After its placement it is slowly inflated by the patient to reach a fluid volume that is equivalent to the volume of the designed skull implant. This is usually a process that takes up to 3 months to achieve sufficient scalp expansion.
Case Study: This female presented skull augmentation for a small head. In determining her exact skull augmentation goals it was determined that the size of the skull implant needed was substantial. Using her 3D CT scan a large custom skull implant was designed with the desired surface area coverage and thicknesses. Its total volume was 225ccs. Given her small head and tight overlying scalp with a history of a strip harvest for eyebrow hair transplantation she required a first stage scalp expansion.
Under general anesthesia and in the prone position with her hair parted along the strip harvest scar, a scalp expander was planned to be placed. A round 14cm diameter tissue expander with a remote port with a maximum inflation volume of 550cc was selected.
Through the existing scalp scar an incision was made and a subperiosteal dissection done over most of her bony skull. The expander was deflated of all air and inserted through the incision until its lower edge was barely seen at the top edge of the incision.
The remote port is then positioned by passing it under the incision and over on top of the deep temporal fascia above the right ear. The scalp incision was closed in two layers with resorbable sutures. Only 10ccs of fill was added to the expander after the incision was closed.
The goal of the tissue expander is to add enough liquid fill to match that of the volume of the designed custom skull implant. The key is to get a tension-free incision closure over the skull implant at the second stage. By adding 10cc every 2 or 3 days through the port it would take around 8 to 10 weeks to achieve the maximum expander fill in this patient.
Case Highlights:
1) Most females with small heads that want a significant skull augmentation require a 1st stage scalp expansion.
2) Any patient for skull augmentation that has had a hair transplant strip harvest scar will need a 1st stage scalp expander.
3) The scalp expander can be placed through the hair transplant harvest scar with little liquid fill at the time of placement.
Dr. Barry Eppley
World-Renowned Plastic Surgeon