[Neuroembryologic considerations on the so-called malformative syringomyelia].

Modern neuroradiological techniques can evidence the presence of liquid-filled spaces within the spinal cord, called syringomyelia. These lesions may be associated with numerous causes, the most frequent of which is an abnormality of the shape of the posterior fossa. Neuropathological analysis of these cavities demonstrates whether they are completely lined by ependymal cells or not. Comparing neuropathological and embryological data suggests that syringomyelia is a secondary deformation affecting a normally-formed spinal cord. The unique case in which such a cavity is really a primary malformation is the so-called myelocytocele. The most frequently encountered lesion associated with syringomyelia is the Chiari abnormality (either type I or II). In this case, the size of the posterior fossa is too small whereas neural elements are normal. Since Chiari abnormality may be familial, some genes are likely to be involved for its generation. In experimental animals, it has been shown that genes belonging to the Hox family or the Mhox gene control the development of the final shape of the occipital bone. Syringomyelia is thus a secondary event affecting the spinal cord and due to a distant cause.