Study of asymmetries of the cranial vault in plagiocephaly.

Organic plagiocephaly is caused by premature synostosis of the coronal suture. The subject is dealt with in the context of a desire to categorize these types of asymmetries and to find asymmetry indices using computed tomography scan images. From a cephalometric point of view, the authors looked for a reproducible reference, independent of the structures to be studied-the vestibular orientation, which is based on the definition of a mediolabyrinthic plane, making it possible to assess the symmetry. One of the problems encountered in this study of the cranial vault is related to the difficulty of determining reproducible cranial indicators. Consequently, the authors propose an alternative method for studying the asymmetry using the tracing, measurement of radiuses, and the ratio between symmetrical radiuses from the origin of the vestibular indicator. When it came to putting this tool into practice, the authors opted to design a customized instrument. The tool was then applied to dry skulls considered to be symmetrical and to a few cases of plagiocephaly before and after surgery. The study of dry skulls, used as a reference, demonstrates the general shape of the curve representative of the symmetry evolution over the entire vault in healthy models. Analysis of pathological cases reveals the asymmetry of the cranial profiles (for example, homolateral frontal flattening, contralateral frontal prominence). It also makes it possible to assess the anterior, posterior, low, or high location of asymmetries of the vault. This analysis enables quantitative assessment of asymmetries using ratios, along with objective evaluation of postoperative results, with demonstration of surgical improvements and overcorrections. This analysis could make it possible to characterize asymmetries according to their shape. An attempted quantitative classification system for plagiocephalies according to four degrees of severity is proposed. The proposed analysis permits an objective, reproducible, and quantitative method for studying cranial vault asymmetries. A study on a larger population would make it possible to confirm these hypotheses and put forward new ones. Prospects for development could relate to study of all asymmetry problems affecting the base of the skull and the face.