Embryologic studies by Woodward et al at the turn of the 20th century shed light on the understanding of vascular congenital anomalies. These anomalies are encountered infrequently in everyday practice. They represent a heterogeneous group of isolated or multiple abnormalities that are sometimes associated with complex congenital syndromes. Most vascular anomalies affect the skin, though any organ system can be involved. Nearly all cutaneous congenital vascular abnormalities are evident either at birth or within the first few weeks of life.
The presence of such lesions at birth and early childhood invokes concern and fear in parents and, in some cases, starts a protracted process of multiple visits to various specialists. Thus, it is mandatory to take the time and diagnose lesions appropriately early on and to ensure that a multidisciplinary team approach be used if the disease process warrants. The first step toward this goal is to obtain a careful history and physical examination, as these can distinguish between vascular tumors and malformations with a diagnostic accuracy exceeding 90%. 
A great deal of confusion surrounds the nomenclature and classification of congenital vascular abnormalities, and as a result, prompt proper diagnosis and appropriate treatment for patients are often lacking. Alarmingly, as reported in one study, as many as one half of patients referred to specialty clinics for vascular abnormalities were diagnosed and monitored incorrectly. 
Accordingly, as put forth by Mulliken et al,  an appropriate start to any discussion of congenital vascular abnormalities should include the distinction between vascular tumors (eg, hemangiomas) and vascular malformations (eg, capillary or lymphatic); the two entities are decidedly different (see Pathophysiology).
The topic of vascular anomalies is quite broad. This article serves as a superficial review covering the major tumors and malformations that the general surgeon or practitioner may encounter. To minimize confusing nomenclature and to organize the discussion of the topic, this article adheres to the Mulliken-Glowacki schema.
Finally, it should be mentioned that many vascular anomalies are found in association with syndromes. A full discussion of such syndromes is outside the scope of this article, but a brief litany of predominant syndromes is mentioned in later sections.
Whereas vascular malformations result from abnormal embryogenesis or early fetal life, vascular tumors are endothelial neoplasms characterized by cellular proliferation and growth. Malformations may involve a single type of vessel (eg, capillary or lymphatic) or may be of mixed variety. In clinical practice, malformations are designated by the predominant channel type and resultant rheologic character (ie, fast vs slow flow).
Vascular tumors encompass a broad range of lesions, including angiosarcomas and tufted angiomas, among others. However, the most common vascular tumor remains the hemangioma, a benign lesion usually found in infants.
Currently, various schemas are used to categorize vascular tumors and malformations, [4, 5] stemming from the original classification described by Mulliken and Glowacki.  The Mulliken and Glowacki classification is based on the pathologic characteristics of the endothelium and the natural course of the lesion. A simplified outline of their original classification of vascular anomalies is as follows  :
Vascular tumors include the following:
Other rare tumors
Vascular malformations include the following:
In 2014, the International Society for the Study of Vascular Anomalies (ISSVA) issued an updated official classification of vascular anomalies.  In this classification, vascular tumors are broadly divided into the the following categories:
Locally aggressive or borderline
Vascular malformations are broadly divided into the following categories:
Anomalies of major named vessels
Malformations associated with other anomalies
The ISSVA classification also specifies individual conditions within these categories.
Hemangiomas appear in the first few weeks of life, as opposed to vascular malformations, which are always present at birth, though they are not always readily apparent. The natural course of hemangiomas is one of spontaneous regression, with only one rare variant that may persist unchanged through an individual’s life.  Conversely, vascular malformations never regress and often grow over time. Hence, as a rule, vascular lesions that persist into adolescence and adulthood are true vascular malformations and should not be referred to as hemangiomas.
Hemangiomas typically have the following three stages, classified on the basis of clinical assessment, microscopic morphology, and immunohistochemical markers  :
Proliferation phase (age <1 year)
Involuting phase (age 1-5 years)
Involuted phase (age >5 years)
Most hemangiomas are small and pose only minor clinical problems before they involute and become clinically silent. However, about 20% pose significant problems and require treatment.  This may result from aggressive growth, proximity to vital structures, or complications such as ulceration, bleeding, or even high output cardiac failure.  Finally, the disfiguring nature of certain lesions may prompt parents to seek intervention early rather than wait for the involution phase.
The pathophysiologic characteristics of vascular malformations are dictated by the type of channels involved (heme vs lymphatic) and the flow characteristics of the resultant lesion. Typically, capillary, venous, and lymphatic lesions tend to be slow-flow, whereas arterial lesions are fast-flow. Any combination of these elements is possible, resulting in an arteriovenous malformation (AVM), a capillary-lymphaticovenous malformation (CLVM), or a lymphaticovenous malformation (LVM). (See Presentation.)
The etiology of a particular vascular anomaly can vary greatly, depending on the nature of the lesion. In general, vascular tumors are endothelial neoplasms, the molecular biology of which remains poorly understood and characterized. There has been considerable interest in the mechanisms underlying the formation of hemangiomas, which are the most common of vascular tumors.
Although data from animal models remain lacking, research performed with human tissues has implicated numerous signal pathways that are altered during the various phases of hemangioma development. These include, among other, the following  :
Basic fibroblast growth factor (bFGF)
Vascular endothelial growith factor (VEGF)
Tissue inhibitor of metalloproteinases 1 (TIMP1)
Hypoxia-inducible factor (HIF)
Apart from these observational data, however, the mechanistic understanding of hemangioma development remains poor. Some authors have suggested a hereditary component to hemangiomas; however, the data are conflicting with respect to this notion. 
Vascular malformations are speculated to arise from abnormalities in the process of normal vascular development. Specifically, perturbation of early angiogenesis and vasculogenesis may result in abnormal vascular channels, leading to the development of vascular malformations.  In contrast with vascular tumors, vascular malformations seem to have a strong hereditary component, with specific lesions observed in the setting of inherited syndromes.
Alterations in several signaling molecules and pathways have been identified in specific types of malformations. For example, TIE2,  glomus cells,  and bFGF  have all been implicated in the formation of AVMs. Investigators have localized chromosomal mutations underlying several combined vascular formation syndromes (eg, Klippel-Trenaunay-Weber syndrome and Proteus syndrome), further supporting a hereditary component to the development of AVMs. [17, 18]
In general, vascular anomalies are rare, and limited data exist regarding their true worldwide incidence and prevalence. However, there is now a growing body of observations detailing the epidemiology and natural history of the more common subtypes of these anomalies (eg, hemangiomas and venous malformations).
Hemangiomas are the most common tumors of infancy and childhood, observed in 4-12% of infants during the first year of life. [19, 20] They are three to five times more common in females than in males. They are also more common in premature infants, with the risk increasing with lower birth weight.  The incidence among nonwhite populations remains unknown; however, hemangiomas in dark-skinned individuals are uncommon. 
Epidemiologic data regarding vascular malformations are also scarce. The overall incidence of congenital vascular malformations in the general population is estimated at 1.5%. Approximately two thirds of malformations are of venous predominance and are evenly distributed according to sex and race. 
In two separate case series, for example, patients with congenital vascular malformations were evaluated at Children's Hospital of Mexico City (1963-1983; 223 children) and the Walter Reed Army and National Naval Medical Centers (1984-1998; 169 children). Of the 392 patients, 257 (65.6%) had malformations of venous predominance. Prevalences of phlebectasia, aplasia or hypoplasia of venous trunks, aneurysms, and avalvulia were also recorded.
Most hemangiomas have a self-limited course, leaving only a mild blemish or nearly imperceptible skin changes at the lesion site. However, the outcome of lesions that require intervention or operative management is heavily influenced by the nature and site of the lesion. For example, facial lesions may result in long-term cosmetic disfigurement.
Most vascular malformations represent progressive lesions, and long-term outcomes vary according to the nature, size, and location of a specific lesion. Lesions such as AVMs and small vascular malformations are more likely to be "cured" with surgical measures than lesions such as lymphatic malformations and mixed lesions are. With all of these lesions, however, long-term follow-up and vigilance are required to determine the efficacy of therapeutic intervention.