Posterior Cranial Vault Distraction Osteogenesis (PVDO)
Posterior cranial vault distraction osteogenesis (PVDO) is a new technique that has emerged as a powerful procedure in treating patients with syndromic bicoronal craniosynostosis. It is performed at major craniofacial centers in Children's hospitals throughout the world to treat syndromic craniosynostosis. Before discussing the procedure let's take a moment to review the head shape that accompanies syndromic craniosynostosis. The two coronal sutures normally provide forward growth of the forehead. In bilateral coronal craniosynostosis the skull is shorter from front to back, wider and also taller than usual. This skull shape that is tall, wide and short from front to back is called brachycephaly. This head shape is the result of growth at the remaining open sutures that must make up for the loss of growth at the closed coronal sutures. In patients with craniosynostosis syndromes such as Apert, Crouzon, Pfeiffer, Saethre-Chotzen and Muenke syndromes, the head shape changes that accompany bilateral coronal synostosis tend to be more dramatic because of additional severe growth disturbance throughout the skull. Often these patients have severe growth disturbance in the skull base (floor of the skull), the back of the head is is often severely flattened and the skull can have a tall and forward leaning look called turribrachycephaly. These patients have such severe growth disturbance of the skull that they often require two or more cranial vault expansions to prevent or relieve increased intracranial pressure and/or normalize appearance. Let's now talk about the concept of distraction osteogenesis.
Distraction osteogenesis (DO) is a technique in which cuts are made in bones and specialized devices (distractors) are placed. Healing is allowed to begin and then the distractors are turned (activated) to move the cut ends of the bones away from one another slowly over time. This creates new bone in the gap and allows for generation of new bone and repositioning of the bones also. This was first used by orthopedic surgeons in limb lengthening surgery. It has now been used in the skull and facial bones for over 25 years.
PVDO uses specialized devices called cranial distractors to move the bones of the back of the skull very slowly. In PVDO the skull bones are left attached to the dura (outer covering of the brain). Cuts are made in the skull bones, similar to open cranial vault remodeling (CVR). However, PVDO allows for more significant reshaping and enlargement of the back of the skull than single stage cranial vault remodeling procedures.
The scalp is usually what limits how much we can expand the size of the skull in a single operation. Cranial distraction allows for more significant reshaping and expansion of the space inside the skull by slowly stretching the scalp over time. The scalp no longer determines the amount of cranial expansion. Now the amount of expansion is only determined by what the patient needs. In addition, new bone forms in the gaps of the cut skull bones. The skull bones don't have to be removed or reshaped which minimizes the morbidity of the surgery compared to open cranial vault surgery.
I have published multiple articles about PVDO and presented my research on PVDO at both national and international meetings. I most recently published an article with colleagues at the Children's Hospital of Philadelphia in which we compared the changes in the size of the skull obtained from frontoorbital advancement and PVDO. Our research showed that PVDO can provide a two-fold greater expansion of the space inside the skull than fronto-orbital advancement. I believe that this is an important consideration when deciding on which procedure is best for your child.
In syndromic craniosynostosis both the front and the back of the skull are severely affected, so fronto-orbital is still required. Read more about front-orbital advancement. However, in patients who do not have exposure issues related to the eyes and eyelid position, PVDO can be used as a first stage procedure (in the first 6 months of life) to provide greater expansion of the skull while the brain is growing most rapidly. This also allows us to delay frontoorbital advancement (FOA) to a later age. The older the patient is at the time of the first FOA the better the long-term results will be. The photos show the changes in the head shape achieved with PVDO performed at age 6 months and FOA performed at age 3 years old.
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