Video clip 1: Area of vascular anomaly with swelling at time 0 of contrast administration. Contrast enhanced ultrasound studies permit detection of small vessels not visualized on conventional ultrasound. This technique allows identification of smaller anomalous vessels, which were not detectable by non-contrast B mode sonography, as in this pre-contrast video clip. Such vasculature may contribute to the pathophysiology of the anomaly, and thus identifying contributory vessels may be useful in planning interventions.