Hemangiomas of infancy are benign (noncancerous) vascular tumors composed of cells that normally line the blood vessels (endothelial cells). They are the most common tumor of childhood, occurring in up to 10% of infants. Hemangiomas are seen in all racial groups but are more common in Caucasians. They also occur more frequently in girls and low-birth-weight (less than 1,000 grams) premature infants.
Hemangiomas of infancy may be visible at birth or may not be recognized until the first few weeks or even months of life. In general, however, most hemangiomas become evident by 2 to 3 weeks of age. Although they commonly occur on the head (illustrations 1-3) or neck (illustration 4) (60%), they can occur in any region of the body (illustrations 5-6). Some lesions are small and hardly visible, whereas others are large and readily observable (illustration 7). Most hemangiomas appear as single tumors, though 15% present with more than one lesion.
The cause of hemangiomas is not yet understood, but it is known that they are not related to drugs or medications that may have been taken during pregnancy, nor are they related to any known environmental exposures that may have occurred during that time. Rarely, in some families multiple family members over several generations have been affected, and this is related to a gene abnormality. Current research is focusing on the hemangioma precursor cell, which will help with our understanding of the origin of hemangiomas. Hemangiomas of infancy almost always have a period of growth, which is referred to as their proliferative phase. This is followed by a period of shrinkage, referred to as their involutive phase (illustrations 8-10). Most hemangiomas begin their proliferative (growth) phase shortly after birth. This phase usually lasts for 4 to 6 months, but can be longer or shorter. Each lesion has its own growth timetable. The involutive phase is much slower and can take as long as ten years. It is difficult to predict how long this shrinkage process will last. Lesions that involute slowly, over a long period of time, are much less likely to shrink completely. In some children, even those hemangiomas that do shrink completely may leave residual fatty tissue and telangiectasias (tiny dilated blood vessels) of the skin.
Rarely, hemangiomas are fully grown at birth and do not increase in size (illustration 11). These tumors are called congenital hemangiomas. Unlike hemangiomas of infancy, congenital hemangiomas either involute rapidly or not at all. Rapidly involuting congenital hemangiomas are referred to as RICH. Noninvoluting congenital hemangiomas are referred to as NICH.