Kasabach-Merritt syndrome (KMS) is characterized by giant vascular tumors and severe thrombocytopenia, which may result in life-threatening multi-organ hemorrhage. The thrombocytopenia associated with vascular lesions is caused by localized consumptive coagulopathy. The vascular lesion triggers intravascular coagulation with platelet trapping and consequent thrombocytopenia, as well as activation and consumption of coagulation factors.  

KMS is associated with kaposiform hemangioendothelioma in over 90% of cases and occasionally with tufted angioma. Kaposiform hemangioendothelioma is typically a solitary tumor which appears in the soft tissues of the limbs, head and neck or retroperitoneum. This vascular tumor is usually seen in infants less than 2 years of age, although cases have been reported in adults. It can cause serious problems because of local growth, cardiac failure or the associated Kasabach-Merritt phenomenon.