A subtype of complex lymphatic anomaly, with some overlap with generalized lymphatic anomaly. It is a rare aggressive disease characterized microscopically by excessive, dilated and abnormally formed lymphatic channels accompanied by scattered clusters of variably canalized, often hemosiderotic, spindled lymphatic endothelial cells. KLA usually presents during childhood, with respiratory symptoms, bleeding, and subcutaneous mass. Potential complications of KLA include thrombocytopenia and hemorrhage. Somatic pathogenic variants in NRAS have been identified in KLA.