Aesthetic cranioplasty often involves the coverage of large skull areas with alloplastic material. Whether it be PMMA or hydroxyapatite cements or with today’s custom 3D generated silicone implants, a fairly large amount of material can serve as a solid interface between the overlying scalp and the underlying cranial bone. As the scalp has an excellent blood supply through major arterial pedicles, the placement of such skull implants do not pose any vascular compromise to the scalp tissues in general or to hair growth in particular.
But there are risks to consider in the use of larger skull implants such as scalp tissue adherence and the development of seromas (fluid collections) after surgery. It is easy to see how these might occur since the scalp normally sticks back down to bone and seals its lymphatic channels by such healing. Any implant material, however, creates a surrounding capsule to which the scalp sticks but the capsule itself does not adhere to the material as firmly as natural scalp tissue sticks to bone. The capsule itself can also be a source of chronic fluid egress particularly in secondary surgery where an established capsule exists.
While the development of these skull implant issues are rare in my experience, there is a simple intraoperative manuever to help their prevention. The placement of many small holes through the material, known as perfusion holes, can help re-establish a fibrovascular connection between the scalp and the underlying skull bone. The more holes that are placed the more small connections that are made. In solid PMMA bone cement 2mm holes are made with a handpiece and burr. It is only necessary to go through the material and not into the bone. But there is no harm in doing so if the outer cortex of the bone is penetrated.
In custom silicone skull implants these perfusion holes are made with a 2mm or 3mm skin punch. This is easy and quick to do. How many perfusion holes to make is not precisely known but more is probably better than less.
The placement of perfusion holes in aesthetic skull implants, in addition to recreating a vascular connection, also serves to have a quilting effect. With the tissue ingrowth through the holes, a small soft tissue ‘anchor’ is created. This in effect takes a large subcapsular space around the implant and turns it into many smaller compartments. This serves not only to anchor the overlying scalp to the implant but also can have a seroma prevention effect.
Dr. Barry Eppley
Indianapolis, Indiana