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- Kaposiform Hemangioendothelioma (KHE) : A rare vascular tumor that is typically diagnosed in infancy or early childhood, with some cases present at birth It is an aggressive disease with high potential morbidity, mainly due to associated consumption coagulopathy (the Kasabach–Merritt phenomenon (KMP)), a disorder characterized by severe thrombocytopenia, hypofibrinogenemia and high D-dimers. KHE and tufted angioma are now viewed as part of the same spectrum of disease.
- Kaposiform Lymphangiomatosis (KLA): 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.
- Klippel-Trenaunay Syndrome (KTS) : The term KTS has been used to denote a combination of CM+VM +/- LM + limb overgrowth. It is not a genomically uniform diagnosis. Many severe cases are due to somatic pathogenic variants in PIK3CA and are now recognized as part of the PIK3CA-related overgrowth the diagnosis of diffuse capillary malformation with overgrowth (see DCMO). Other cases with overgrowth and vascular birthmarks in association with higher flow vascular anomalies fit best as “Parkes Weber syndrome”, a separate diagnostic entity. Note: The term Klippel-Trenaunay-Weber syndrome is not correct. It has had moderately widespread use in the pediatric literature, after it appeared in some textbooks, but it is a mixture of two distinct syndromes, Klippel-Trenaunay and Parkes Weber and should not be used spectrum (PROS). Other cases which mimic the definition of KTS are due to GNAQ/GNA11 somatic pathogenic variants and most often best fit with [missing copy here].
