Single dominant lesion in capillary malformation‐arteriovenous malformation (CM‐AVM) RASA1 syndrome.

We report two cases with localized vascular malformations clinically resembling the "dominant lesion" seen in capillary malformation‐arteriovenous malformation (CM‐AVM) syndrome, however, lacking germline RASA1 variants but presenting double somatic RASA1 variants in affected tissue. Both patients presented with localized and superficial high‐flow vascular malformations were treated with surgery and laser therapy and showed partial resolution. The study underscores the rarity of somatic RASA1 variants, contributes to understanding the "second‐hit" pathophysiology in vascular lesions, and emphasizes the significance of clinical distinctions and genotyping for accurate diagnoses, offering implications for diagnosis, prognosis, and genetic counseling. [ABSTRACT FROM AUTHOR]