Klippel–Trénaunay syndrome

Klippel–Trénaunay syndrome, formerly Klippel–Trénaunay–Weber syndrome and sometimes angioosteohypertrophy syndrome and hemangiectatic hypertrophy, is a rare congenital medical condition in which blood vessels and/or lymph vessels fail to form properly. The three main features are nevus flammeus (port-wine stain), venous and lymphatic malformations, and soft-tissue hypertrophy of the affected limb. It is similar to, though distinct from, the less common Parkes Weber syndrome.

The classical triad of Klippel–Trenaunay syndrome consists of:

1. vascular malformations of the capillary, venous and lymphatic vessels;
2. varicosities of unusual distribution, particularly the lateral venous anomaly; and
3. unilateral soft and skeletal tissue hypertrophy, usually the lower extremity.

It belongs to the PIK3CA-related overgrowth spectrum of diseases which are caused by mutations in the PIK3CA gene.