Vascular anomalies include a large and heterogeneous group of entities that frequently present in children. The most widely accepted classification of vascular anomalies is that proposed by the International Society for the Study of Vascular Anomalies (ISSVA) in 1996, most recently revised in 2018 [1], which categorizes these lesions in two distinct groups: vascular tumors and vascular malformations. The ISSVA classification provides the standardized nomenclature that facilitates communication between radiologists and the other clinicians, which is of the utmost importance since the evolution, treatment and prognosis of many of these lesions can be substantially different.
Vascular tumors refer to lesions that show endothelial hyperplasia and growth and include benign lesions such as infantile and congenital hemangiomas, locally aggressive or borderline lesions such as kaposiform hemangioendothelioma, and rare malignant lesions such as angiosarcoma and epithelioid hemangioendothelioma.
Vascular malformations refer to congenital lesions characterized by abnormal morphogenesis of specific vessels but with normal endothelial cell turnover and only weak endothelial cell proliferation [2]. These can be categorized into simple (capillary, venous, lymphatic or arteriovenous), combined, of major named vessels, associated with other anomalies (commonly overgrowth), and provisionally unclassified.
The diagnosis of vascular anomalies can often be made on clinical grounds or with the help of ultrasound [3, 4]. MRI is often requested when ultrasound has not provided diagnosis or has not shown the full extent of the lesion, when assessing large and deep lesions, when the lesion is associated with other anomalies such as overgrowth, and as a baseline or follow-up to monitor treatment response. It is important to emphasize that the interpretation of imaging findings has always to be correlated with the clinical findings and the radiologist should make an effort to have all relevant clinical information at the time of doing MRI.
MRI is performed using the smallest coil that includes the entire lesion with acquisition in at least two orthogonal planes. A combination of sequences is routinely used including spin echo T1 and fat-suppressed T2 (or STIR) [5]. Gradient-echo sequences may also be used to facilitate identification of hemosiderin, particularly when assessing venous malformations involving a joint [6], and to detect intralesional high-flow vessels. The examination is followed by contrast-enhanced MR angiography ideally using a 3D time-resolved technique that allows better differentiation of arterial from venous flow and detection of early venous filling [7]. The exam then concludes with at least one fat-suppressed T1 sequence that allows assessment of delayed enhancement and may provide further anatomical detail. Diffusion-weighted MRI may be added when the differential diagnosis includes a malignant neoplasm.
This presentation will illustrate characteristic MRI findings that allow the diagnosis of the most relevant pediatric vascular anomalies using the ISSVA classification.

Acknowledgements

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