CP and acute lymphoblastic leukemia: As commented above, ALL cell lines have been described as able to cross CP epithelial cell monolayers [24, 25]; however, in our immunofluorescence and electron microscopy studies, only exceptionally did we find leukaemic cells in transit from the basal to the apical surface of the CP epithelium, suggesting that the BCSFB is a minor pathway for leptomeningeal dissemination, as has also been pointed out by other authors [5, 29].