Infantile haemangioma: part I. Pathophysiology, epidemiology, clinical features, life cycle and associated structural abnormalities.

Infantile haemangioma (IH) is the most common tumour of infancy. Its typical natural history is characterized by an early rapid growth following birth and a slow spontaneous regression phase within a period of 3 to 7 years. The exact aetiopathogeny underlying IH is still to be fully understood, but the role of fetal hypoxic stress is strongly suggested as a triggering signal in epidemiological studies. IH are composed of a complex mixture of cells including multipotent stem cells, a majority of immature endothelial cells, pericytes, dendritic cells and in the late stage, adipocytes. Most of IH are nodular and are not associated with malformations. However, in some cases, IH referred to as segmental may be associated with developmental abnormalities such as PHACES and PELVIS/SACRAL syndromes.