Until recently, the treatment of congenital vascular lesions lacked a protocol. This stemmed, in part, from the absence of a uniformly accepted classification and the lack of a clear understanding of the natural history of these lesions. Further compounding the problem was the widely held notion that, given time, most such lesions would spontaneously resolve. Congenital vascular lesions were therefore misdiagnosed and, for the most part, left untreated. The plight of these unfortunate patients led them from physician to physician in search of help.
The renaissance began with a (biologic) classification first proposed by Mulliken and Glowacki . They dispensed with the old, often confusing terminology and replaced it with a clear, concise set of terms and definitions. Mulliken and Glowacki recognized two entirely distinct groups of congenital vascular lesions: hemangiomas and vascular malformations (Table 1). They defined hemangiomas as lesions that were usually not present at birth, proliferated during the first year of life, and then involuted over the ensuing years. The term "vascular malformations" was reserved for lesions that were always present (although not necessarily apparent) at birth, never proliferated, and never involuted.
Most hemangiomas first appear soon after birth, but as many as 30% may be apparent at birth . They characteristically proliferate during the first year of life and then involute sometime during childhood.
Although the rate and timing of proliferation within this period is extremely variable, two periods of rapid growth are frequently seen. The first and most common of these proliferative phases takes place during the neonatal period and early infancy and the second, between 4 and 6 months of age. Histologic features of proliferation include tubules of plump, proliferating endothelial cells with frequent mitoses and an abundance of mast cells. Little or no intervascular stroma is apparent, and the lesion appears cellular (Figure 1).
Hemangiomas may originate in the superficial papillary and/or reticular dermis. These lesions were previously known as capillary hemangiomas, but have been renamed cutaneous hemangiomas (Figure 2). Lesions that arise from deeper subcutaneous tissues, previously known as a cavernous hemangiomas, are now termed subcutaneous hemangiomas (Figure 3). Hemangiomas that stem from either the superficial or deeper tissues but extend across both planes are referred to as compound hemangiomas .
Proliferation invariably slows by the end of the first year of life, and a long period of involution follows. During involution, the once active proliferating endothelial cells become less active and progressively flatten until late in involution, when they are not dissimilar from cells seen in normal vascular channels (Figure 4). The involution process is usually accompanied by an increase in intervascular fibro-fatty tissue, which eventually replaces most of the hemangioma. Thus, the lesion changes from a predominantly cellular to a predominantly vascular tumor and finally to a fibro-fatty mass of tissue with a few ectatic vascular channels.
Rate and Patterns of Involution--The rate of involution is extremely variable. To date, no known characteristics appear to influence either the rate or completeness of involution.3 Waner and Suen have identified two distinct patterns of involution (Figure 5). In the first group, lesions involute rapidly, and the involution process is complete by between 5 and 6 years of age. This group is more likely to have a satisfactory outcome and are thus less likely to require corrective surgery. Finn et al reported that only 40% of such patients required corrective surgery .
In the second group, lesions involute at an extremely slow rate; this may take up to 12 years and is less likely to be complete. Approximately 80% of patients with this type of lesion ultimately require corrective surgery.
The diagnosis of a hemangioma is made, for the most part, on clinical grounds. The classic feature, namely, proliferation during the first year of life, sets this lesion apart from all other vascular lesions. A superficial or cutaneous lesion is a red, bosselated mass, whereas a deeper lesion presents as a bluish mass. The mass is much firmer during proliferation and softer and more easily compressible during involution. Parents often notice the mass expanding when the child cries or the lesion is in a dependent position.
Subcutaneous hemangiomas are often more difficult to diagnose. When the diagnosis is in doubt, an MRI is useful in confirming the presence of a hemangioma. Hemangiomas are high-flow, solid-tissue lesions of intermediate intensity on T1-weighted presaturation images.