Histogenesis of hemangiomas--an ultrastructural study on capillary and cavernous hemangiomas of the skin.

13 capillary hemangiomas of the skin were examined by electron microscopy in order to elucidate their histogenesis. The findings show that the histogenetic development of hemangiomas is similar to that of embryonal and fetal capillaries. Initially the undifferentiated angioblastic anlage gives rise to solid buds, which subsequently receive a lumen, thus turning into primitive capillaries. This developmental stage corresponds to early embryonic vasculogenesis. The growth of angiomas is mainly due to sprouting, which as in fetal and postnatal vasculogenesis takes place from both primitive and mature capillaries. These findings support the classical theories on the histogenesis of angiomas (angioblastic and sprouting theories). The question whether in all cases hemangiomas have to pass through all developmental stages or whether it is possible that part of them develops directly from the normal capillary network of the skin by a process of sprouting remains open to discussion. Finally the findings in one cavernous hemangioma and two tele-angiectasias were compared and discussed.