Of all the non-craniosynostotic developmental skull deformities that exist, by far the most common is occipital plagiocephaly. This refers to a flattening on one side of the back of the head. While the deformity may be greatest on the flattest part of the occiput, its effects go beyond the flat skull area. Usually there is some compensatory bulging on the opposite normal side of the occiput as well as on the temporal side of the flattened side anterior to it. The ear positions can also be seen to be asymmetric with the ear on the flattened side more anterior than the opposite ear and may have some slight protrusion to it as well.
While a flat back of the head in an adult poses only an aesthetic deformity, to some so afflicted it can be more than just a casual asymmetric concern. While an occipital plagiocephaly in a balding male or one who shaves his head appears obvious and their concern is visible, I have seen an equal number of women with full heads of hair that are considerably bothered by it as well and adjust their hairstyles to accomodate for the aesthetic skull deformity.
The correction of an occipital flattening is done by building up the back of the head with a cranioplasty material. In and of itself, it is a fairly straightforward procedure to accomplish skull symmetry as long as one has complete visual access. Using a traditional and full ear to ear incision with peelback of the scalp does allow this exposure but many patients do not desire a full transverse scalp scar. This would be particularly true in almost all men due to their hair density and scar exposure concerns. It is always paramount to avoid trading off one aesthetic scalp/skull problem for another.
Adapting an occipital cranioplasty procedure through a smaller incision has been necessitated over the years because of scar concerns. It is possible to do the procedure but it necessitates several technical adjustments or modifications to that of a full open cranioplasty. It does not require special instrumentation but an intimate working knowledge of the handling properties of the various cranioplasty materials.
First and most importantly only one cranioplasty material has the working properties to be inserted through a small incision and molded into shape externally by scalp manipulation. PMMA or polymethylmethacrylate, acrylic bone cement, can be mixed into a putty which at a certain point in its set is not too loose but has not started to fully polymerize either. It is this window in the setting of the material that can permit it to be inserted through a smaller incision and still have adequate flow properties to be molded once inside. Unfortunately, none of the HA or hydroxyapatites have these working propertiues to be of great value for this approach. I have tried every HA material available and they all come up wanting, either in too short of set times or lack of adequate flow characteristics.
While a cranioplasty material can not really migrate around or away from its pocket on the bone, like other implants in soft tissues, some anchorage to the bone is always a good idea…even if it is just for psychological reassurance The best way to do that is to place small 1.5mm self-tapping titanium screws into the bone leaving them slightly above the bone surface. This will allow the PMMA to flow around them and lock onto them while it is curing. Since PMMA never really bonds to the skull bone, although there is some justification to calling it a bone cement since it does have some stick to it, this small screw fixation certainly prevents any micromovement. As long as too many screws are not placed or the screws are not too big, it is really quite easy to pop the implant off the bone later should that ever be necessary. In essence, their use does not make secondary removal unduly difficult.
Once the PMMA material is inserted, the scalp incision needs to temporarily stapled together. This then allows one to shape the material and feather its edges by external scalp manipulation. There usually is a few minute window to do the molding. While in years past the final set of PMMA was associated with very high heat release, this is no longer true. The exothermic reaction is very minimal with newer formulations so there is no risk of thermal injury to the scalp tissues. Once shaped and set, the staples are removed and partial visual assessment can then be done internally. (although this will be very limited as the material now occupies the entire pocket and the small incision makes it very hard to look over all the augmented area)
One advantage to the small incision cranioplasty is that the risk of difficulty with incisional closure is less because the molding is usually done away from it. This prevents the risk of encountering an incision that can not be closed due to the augmentation volume. When possible it is always best to have an incision in which no cranioplasty material lies underneath it. (ideal but not always possible)
The small incision occipital cranioplasty can be a very effective method of skull augmentation. Patients can have a very quick recovery and very minimal discomfort. But it is very technique dependent and requires good experience with more open methods of cranioplasty before attempting it through limited access.
Dr. Barry Eppley