Angioma serpiginosum is a vascular nevus characterized by a progressive, noninflammatory ectasia of superficial dermal capillaries. It is clearly unrelated to the "pigmented purpuric eruptions" with which it is frequently confused but has many clinical and histologic features in common with angiokeratoma circumscriptum and nevus flammeus.
STEVENSON JR, LINCOLN CS. Angioma Serpiginosum. Arch Dermatol. 1967;95(1):16-22. doi:10.1001/archderm.1967.01600310022004