Naevus vascularis mixtus and mixed vascular naevus syndrome.

Naevus vascularis mixtus (NVM), or mixed vascular naevus (MVN), is a binary phenotype resulting from allelic twin spotting, consisting of a naevus anaemicus paired with a telangiectatic naevus reminiscent of naevus roseus, and caused by a mosaic GNA11 mutation. MVN syndrome is characterized by an NVM associated with soft tissue hypotrophy or central nervous system abnormalities, mainly involving the cerebral vasculature. The differential diagnoses of NVM and its syndrome include vascular twin naevi, syndromes featuring naevus flammeus and other port-wine naevi, and the various types of phacomatosis pigmentovascularis. NVM and MVN syndrome are rare but probably underdiagnosed and under-reported.