Over the years, a variety of different approaches have been employed to better understand and categorize congenital vascular anomalies in infants and children. Throughout most of last century the myriad of vascular anomalies were lumped together, and were generically referred to as “vascular birthmarks.” The first concise and widely accepted classification system was proposed in 1982 by Mulliken and Glowacki. In this landmark paper, vascular anomalies were separated by their biological and pathological differences into the common infantile hemangiomas and the vascular malformations. This classification was further refined by the International Society for the Study of Vascular Anomalies (ISSVA) in 1996 in several ways. The current ISSVA classification of vascular anomalies recognizes that the common infantile hemangiomas are part of a larger spectrum of proliferative vascular anomalies, which also includes congenital hemangiomas, tufted angiomas, and the various types of hemangioendotheliomas. Proliferative vascular anomalies demonstrate abnormal mitotic activity and cellular hyperplasia; the common infantile capillary hemangioma is indeed the most frequent lesion in this category. These lesions should be differentiated from the non-neoplastic vascular malformations, which are a result of abnormal vascular morphogenesis rather than abnormal cell turnover. Vascular malformations are further subdivided into distinct categories based on the primary channel type that is manifested in the lesion. The channel types include capillary, venous, lymphatic, arterial, or combined/mixed lesions. Any lesion with an arterial component is deemed a high-flow vascular malformation, whereas all other are considered low-flow vascular malformations. Finally, a separate category containing rare lesions that demonstrate overlap between proliferative anomalies and vascular malformations was created to account for these unusual vascular anomalies.
The vast majority (90%) of vascular anomalies can be distinguished on the basis of clinical history and physical examination. However, imaging is often employed to evaluate lesions that are clinically suspected to extend into the deep tissues. Imaging can also delineate the vascular supply and drainage of larger or high flow lesions while at the same time potentially revealing other associated anomalies. Imaging can not only play a vital role in the initial diagnostic work up of certain vascular lesions, but can also help with treatment planning and post treatment assessment.
Goals of imaging peripheral vascular anomalies are three-fold, and include defining the anatomic extent of the lesion, identifying arterial supply and venous drainage, and using this radiologic information in conjunction with available clinical data to classify the lesion per the ISSVA classification scheme. MRI is rapidly becoming the ideal non-invasive modality in that this single examination can address all three goals, and often obviates the need for more invasive radiologic workup. It is by far the most informative study with respect to lesion extent, as the vast majority of these lesions are markedly hyperintense on T2-weighted images and therefore stand out particularly well on fat-suppressed or inversion-recovery sequences. MR also provides valuable information on flow characteristics of the lesion. With recent advances in parallel imaging and creative methods of populating k-space, temporal vascular information can be obtained by the use of time-resolved imaging, further improving one’s diagnostic yield with respect to lesion vascularity. MR does all this without employing iodinated contrast or ionizing radiation, the latter factor being particularly important when one realizes that the majority of these lesions occur in children. MR is becoming widely accepted as the best imaging modality for the evaluation of vascular anomalies, both in children and adults.
Capillary Hemangiomas
Capillary hemangiomas are the most common vascular tumor of infancy. These benign tumors may present at birth, though often they are not discovered until several weeks later. Cutaneous capillary hemangiomas classically have a soft strawberry-like appearance, though deep lesions may have a deep, bluish-hue (Fig. 1). Manual compression does not result in appreciable blanching of a hemangioma. These tumors are more common in girls, caucasian patients, and in very low-birth weight infants. Approximately 80% of patients have a solitary cutaneous lesion, with the remaining 20% having multiple cutaneous lesions. A patient with multiple lesions (eg >= 5) is at higher risk of having visceral hemangiomatous involvement, with the most common visceral sites involved being the liver, lungs and gastrointestinal tract, in that order. Appearance on MR varies depending on stage of growth of the hemangioma. In all instances, these mass lesions are uniformly and markedly hyperintense on T2WI, they have numerous large-caliber flow voids, and are high-flow lesions on time-resolved imaging. Post-contrast sequences demonstrate uniform contrast enhancement (Fig. 2, 3). During the involution phase, these lesions shrink in size, and linear regions of T1 hyperintensity are identified on non-fat suppressed T1WI due to fibrofatty tissue proliferation. Progressive loss of lesion vascularity is also noted.
Fig. 1: Capillary hemangioma isolated to the scalp (a). Separate patient with multiple confluent hemangiomas in a beard distribution (b) as a part of the PHACES syndrome.
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