1.1 Introduction

The key to understanding vascular anomalies is speaking a common language so that pathologists, clinicians, and researchers use a consistent terminology. This is important, as it is essential to appreciate that not every benign vascular lesion is a hemangioma. Classification systems importantly provide common terminology and serve as a guide for diagnosis, management, and research endeavors. Fig. 1.1 , Fig. 1.2 , Fig. 1.3 , Fig. 1.4 , Fig. 1.5 , Fig. 1.6 , Fig. 1.7 , Fig. 1.8 , Fig. 1.9 , Fig. 1.10 , Fig. 1.11 , and Fig. 1.12 demonstrate several types of hemangiomas and vascular malformations described throughout the text and tables.

Malan and Puglionisi were the first to distinguish vascular malformations based on vessel type and flow characteristics. ^{1 ,​ 2} As a result of a workshop in Hamburg, Germany, in 1988, the Hamburg Classification evolved to replace commonly used eponyms, separate vascular malformations anatomically based on predominant vessel type, and further categorize into truncular (involving major axial vessels) or extratruncular (involving branches of major vessels) features. ³ This classification has been further refined and is shown in Table 1.1 . ^{4 ,​ 5} Abnormalities of truncular vessels include aplasia or obstruction, stenosis, coarctation, dilatation, agenesis, or aplasia on the one hand and aneurysms or persistent embryonic channels or aneurysm; extratruncular pathologies can be local or infiltrating. Extratruncular and truncular forms are believed to result from developmental arrest in early and later embryogenesis, respectively. ⁵

Mulliken and Glowacki then proposed a classification ( Table 1.2 ) based on clinical and endothelial cell characteristics. ⁶ This classification provided the first fundamental separation of vascular anomalies into lesions with a proliferative component (vascular tumors) versus relatively static vascular malformations (based on principal anomalous vasculature) in an article that greatly influenced the field of vascular anomalies and is reported to be the most frequently cited article in the plastic surgery literature. ⁷

The table was further refined by the 1996 workshop of the International Society for the Study of Vascular Anomalies (ISSVA), augmenting the more rudimentary previous classification and providing a basic separation of lesions based on histologic and rheologic features; new subcategories of diagnoses; and updated histologic, genetic information, and syndromes ( Table 1.3 ). These distinctions provide a framework to provide a common nomenclature and distinguish vascular anomalies into functional and descriptive categories, enabling optimal assessment and treatment for patients. ^{5 ,​ 8 ,​ 9}

One publication examined the significance of histopathologists to incorporate this classification in the evaluation of vascular anomaly samples, underscoring the impact of ISSVA classification in attaining the appropriate diagnosis. ¹⁰ However, vascular anomalies represents a spectrum, and there may be overlapping features of a vascular tumor and malformation in one patient. ¹¹ Additionally, more accurate diagnoses can be achieved by providing adequate clinical information to radiologists and pathologists who are aligned with this terminology. ^{12 ,​ 13} An updated ISSVA classification, which incorporates new entities, genetic and pathology information, was approved by the ISSVA membership in April 2014 and is available for citation from the ISSVA website, http://www.issva.org.

Complementary to the ISSVA classification are staging systems for specific vascular malformations, which some clinicians find advantageous in treatment planning. Schobinger presented a staging schema for arteriovenous malformations (AVMs) based on clinical behavior, from quiescent to destructive ( Table 1.4 ). ¹⁴

Two groups endorsed a staging system for cervical lymphatic malformations based on disease extent, suggesting a correlation between stage, complication rate, clinical or surgical outcome, and prognosis. ^{15 ,​ 16} In addition to providing guidelines for management by forecasting prognosis, the use of consistent terminology can provide uniformity in clinical, surgical, and radiologic research reporting ¹⁷ ( Table 1.5 ).

Other groups have suggested classifications with potential prognostic and treatment-related implications; for example, venous malformations can be classified according to the degree of dysplasia and drainage pattern, based on clinical severity, degree of valvular incompetence, and other measureable changes, or the CEAP (Clinical, Etiological, Anatomical, and Pathological elements) classification. ^{18 ,​ 19 ,​ 20}

Nonetheless, a thorough history (including family history), physical examination, and appreciation of anatomical patterns of distribution of vascular lesions facilitate ascertainment of the correct diagnosis, evaluation, and management plan. Incorporating the age of presentation (prenatal, congenital, postnatal), clinical behavior (static, proliferative, involuting), location, and number of lesions and appreciating existing and impending morbidities are important in determining the extent and pace of further evaluation and potential intervention. Ascertaining the correct diagnosis remains a problem, however, and it is not unusual to receive a radiology or pathology report stating that the diagnosis is most compatible with hemangioma when clearly it is a vascular malformation.

Multidisciplinary vascular anomalies teams have been established in many institutions, providing a structured forum for expert subspecialists to review diagnostic studies and assess patients with vascular anomalies, most of whom require input from more than one medical discipline. This need is underscored by the high incidence of incorrect diagnoses of referred patients. ²¹ One study approximated that PubMed-listed publications during 2009 containing the term hemangioma was used to describe a vascular anomaly in 71.3% of publications, independent of medical subspecialty, concluding that “terminological imprecision is prevalent among both medical and surgical fields. Inaccurate designation of the vascular anomaly is associated with an increased risk of erroneous management.” ²² Correspondingly, the same researchers reported an incorrect referral diagnosis in 47% of patients referred to their vascular anomalies multidisciplinary referral center. ²³ Classification of vascular anomalies can also be viewed by the time of presentation: prenatal, postnatal, and evolving over time.