[Cranio-cerebral dermoid and epidermoid cysts. Classification and pathogenesis].

The pathogenesis of cranial dermoids and epidermoids is still controversial, owing to the multiple etiologies and locations of these lesions. We reviewed 25 cases, classified as follows: extradural lesion of the calvarium; of the occipital squama; dysraphic occipital lesions; and strictly intradural lesions. In the latter group, all lesions but one were in a paramedian, prenevraxial situation, and could be classified 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 hypotheses are studied. Inclusion of epidermal nests at different levels might result from traumatism, dysraphism, or developmental trouble in the lamination of the different layers of the meninges. Most intradural lesions trent to be related to the formation of Rathke's pouch and closure of the anterior neuropore.