The effects of scalp expansion on the cranial bone: a clinical, histological, and instrumental study.

The effects of chronic compression of the cranial bone due to progressive expansion of the scalp have been investigated. Ten patients were studied, 6 adults and 4 children, who were treated for congenital (microtia) or acquired (burns or traumatic) deformities by chronic expansion over a 2-month period. All underwent computed tomography scans of the expansion site prior to introduction of the expansion device, immediately before removal, and at 9 months after the operation. A case of postburn alopecia was lost to the study, because the patient, who had ultimated scalp expansion, did not return for flap advancement. Instead, she came back 3 months later, without the expander, which had been removed at another institution following an automobile accident. In this case, because of slower healing, we performed computed tomography scans 18 months postoperation. During the second procedure (expander removal and flap transposition), bone samples for histological examination were collected directly underneath and along the perimeter of the expanders. Macroscopically, the bone appeared thinned and had a reduced convexity. This reaction, although temporary, appeared more intense in the children and in the posttraumatic cases. Histological examination showed osteoclastic activation, bony hypotrophy, and reaction (deposition of osteoid matrix) under the device, with consequent bone resorption and remodeling. A marked hyperplasia with a hyperostotic reaction was observed around the expanders. At 9 months postoperation, in most cases, a complete normalization was confirmed by computed tomography scans. Expansion of target (fontanellar and sagittal) areas of the skull in children, as well as previous trauma to both scalp and skull should be taken into consideration as a risk factor. Further investigations are suggested.