Pathogenesis

The classification scheme of Waner, although simple and clinically useful, ignores other intriguing facts about hemangiomas that may give clues to their origins. Investigations into the molecular factors controlling the growth and subsequent involution of hemangiomas have identified several factors, which have phase-specific expression patterns and thus may have roles in the growth and involution of these lesions. Proliferative hemangioma have been shown to have high levels of basic fibroblast growth factors (b-fgf), proliferating cell nuclear antigen, type IV collagenase, vascular endothelial growth factors, urokinase and, most recently, insulin-like growth factor 2. Involuting hemangiomas have been characterized by exhibition of tissue inhibitor metalloproeinases, thrombospondin, angiostatin, endostatin, interferon-a, and decreased levels of other factors seen in the proliferative hemangioma. In addition to this information, it has recently been shown that endothelial cells are of clonal origin and the defect which leads to the tumor growth and altered expression of growth factors is intrinsic to the endothelial cell.4 These clonal endothelial cells have also been shown to have characteristics similar to placental endothelial cells, which has led to the hypothesis that these cells may be of placental orgin.

Most commonly, diagnosis is confidently determined by history and physical examination. Typically the history will reveal that more than 50% of hemangiomas are seen at birth as a prominent cutaneous mark. This may manifest as a whitish patch, an anemic nevus, a faint telangiectasia or a blue spot. Rapid proliferation of this initial lesion is highly suggestive of a hemangioma. A superficial hemangioma will assume the typical strawberry appearance making the diagnosis obvious. In cases of subcutaneous, intramuscular or visceral tumor the diagnosis may be uncertain. In these instances various radiologic modalities can be very helpful. MRI is the most informative of the available modalities.

In the case of a two to six month old with progressive stridor, or persistent "croup", consideration should be given to the possibility of a subglottic hemangioma. This is said to be more common in children with a cutaneous hemangioma in a facial or "beard distribution". In these instances, diagnosis should be made with a direct laryngoscopy and bronchoscopy.