Morphological study of anomalous "laminated" brood capsules in cystic echinococcosis in humans and sheep.

"Anomalous", as yet unreported forms of brood capsules (BC) in cystic echinococcosis larvae from humans and sheep are described, thought to be the likely effect of degenerative involution of the parasite. Morphological examination showed an inner laminated layer (LL) in the brood capsules in intimate contact with the internal wall surface, suggesting the term "laminated brood capsules" (LBC). Analysis conducted on LBC from cysts of different typology invariably revealed them to contain just dead and highly degenerated protoscoleces (PSC). Structural and ultrastructural aspects of these peculiar forms are described and possible processes of formation discussed. Comparison of germinal layer (GL), BC wall and PSC organization recognize a "tegumental" and a "non-tegumental" pole, coinciding in GL and PSC and inverted in BC. A quite reversible PSC-or-LL switch governed by complex mechanisms is proposed, of which PSC viability/death is assumed to be an essential part, that under certain conditions makes in vivo LL production inwards possible in BC.