[Pathology and pathogenesis of haemangiomas]

Haemangiomas are tumours of infancy that are characterised by an initial phase of proliferation followed by an involution that, in the majority of cases, results in complete regression. From the pathological point of view, this is a hyperplasic proliferation of endothelial cells, which in the phase of proliferation form highly cellular masses with scarce vascular lumina, invading the dermis and/or subcutaneous cellular tissue. Cellularity diminishes in the phase of involution, the vascular lumina increases and there is a total, or near total, replacement by residual fibroadipose tissue. Its pathology is not well known and two theories are at present postulated: on the one hand, an intrinsic defect of the precursor endothelial cells that, through somatic mutation in a gene regulating angiogenesis, develop a phenotype that induces clonal proliferation. On the other hand, it might arise from cells originating in the placenta that embolize in foetal tissue during pregnancy or delivery. The similarities in antigen expression between haemangioma cells and placenta tissue support this second hypothesis.