CRANIAL DERMOIDS AND EPIDERMOIDS - CLASSI FICATION AND PATHOGENESIS

The pathogenesis of cranial dermoids and epidermoids is still controve rsial, owing to the multiple etiologies and locations of these lesions . We reviewed 25 cases, classified as follows : extradural lesion of t he calvarium; of the occipital squama; dysraphic occipital lesions; an d strictly intradural lesions. In the latter group, all lesions but on e were in a paramedian, prenevraxial situation, and could be classifie d according to their situation relative to the tentorium cerebelli. In our series, strictly intradural dermoids are more often in a rostral situation, and epidermoids in a more caudal situation. Dermoids appear earlier in life than epidermoids, suggesting a more rapid growth due to eccrine secretion. For each group of lesions, the pathogenic hypoth eses are studied, Inclusion of epidermal nests at different levels mig ht result from traumatism, dysraphism, or developmental trouble in the lamination of the different layers of the meninges. Most intradural l esions trent to be related to the formation of Rathke's pouch and clos ure of the anterior neuropore.