Fibrinous vasculosis in the human placenta.

Summary Approximately 6 per cent of placentae of babies admitted to a special care paediatric unit show evidence of peripheral villous stem branch oedema. In more than half of these cases there is evidence of fibrinous vasculosis (FV) in truncal veins. The affected placentae are generally thick and of small diameter, often of extrachorialis type, very congested and often cyanosed. The aetiology of the lesions is discussed with reference to abnormal fetal vascular patterns, poor perfusion, anoxia, oedema and spasm and the effect such factors may have on vessels with an irregularly distributed muscle coat and tendency to a spiral course. A small heterogenous group with FV lesions unassociated with stem branch oedema was also identified. Chorionic vessels were more commonly involved in this group, and it would seem that, in addition to the other factors mentioned above, pressure variations may have some aetiological significance. Lesions of FV occurred mainly in mature placentae. The mothers showed a high incidence of pregnancy-induced hypertension and other complications. Fetal distress and asphyxia at birth were common. Where chorionic vessels were involved there was a high risk of intrauterine death (40 per cent) and coagulopathy among survivors (46.7 per cent). FV lesions affecting truncal vessels carried no greater risk than truncal arterial thrombotic lesions, which have been assessed in the past. In both these groups the hypoxia and intrauterine growth retardation which the babies showed are probably the most important factors, though one could postulate that their clotting mechanism was already triggered.