Hemangiomas are the most common tumors of infancy.
They are more common in females than in males (3:1),
in white populations, and in premature infants. Most of
these neoplasms are located in the head and neck.
Hemangiomas exhibit a
period of rapid postnatal growth. The duration of the
proliferative period is variable, but is usually confined to
the first year of life. The proliferative period rarely
extends to 18 months. The involutional phase is also
variable, occurring over a period of 2 to 9 years.
Hemangiomas can be classified as superficial deep or combined.
Superficial hemangioma replaces the older terms capillary hemangioma and “strawberry” hemangioma and refers to hemangiomas located in the papillary dermis.
Deep hemangioma, often slightly blue in color, originates from the reticular dermis or the subcutaneous space and in the past was referred to as a cavernous hemangioma.
The combined hemangioma has elements of both the
superficial and the deep hemangioma.
Proliferative hemangiomas have been shown to express
high levels of indolamine 2,3-dioxygenase (IDO), basic
fibroblast growth factors (β-fgf), proliferating cell
nuclear antigen, type IV collagenase, urokinase, and,
most recently, insulin-like growth factor 2. Involuting
hemangiomas have been characterized by exhibition of
tissue inhibitor of metalloproteinase 1 (TIMP1), thrombospondin,
interferon-α, and decreased levels of other
factors seen in the proliferative hemangioma.
In addition, it has recently been shown that endothelial
cells are of clonal origin and the defect that leads to
tumor growth and the altered expression of growth factors
is intrinsic to the endothelial cell. These clonal endothelial
cells have also been shown to have characteristics
similar to placental endothelial cells, which may suggest
that hemangiomas are of placental origin. A higher rate
of hemangioma is found in children whose mother
underwent chorionic villus sampling, which gives additional
weight to placental origin theories.
Recently, the primary clonal cell of the hemangioma
has been shown to have characteristics of a myeloid cell,
demonstrating that it is not a typical endothelial cell