Background
Localized intravascular coagulation (LIC) is common in patients with VMs. Large malformation size, involvement of deep structures, diffuse nature, and presence of palpable phleboliths are associated with the presence of LIC (40,41). LIC is a consumptive coagulopathy, characterized by elevated d-dimer, and in more severe cases, low fibrinogen and thrombocytopenia. The exact mechanism driving LIC is unknown, but slow blood flow within malformed venous channels is thought to lead to activation of the coagulation system and consumption of clotting factors (42). Progression to overt DIC can occur in the setting of stressors such as infection (43), sclerotherapy (44), or surgery (45). It is important to distinguish LIC from the Kasabach-Merritt phenomenon (KMP), which occurs in vascular tumors such as kaposiform hemangioendothelioma and tufted angioma. LIC is characterized predominantly by clotting factor consumption, while KMP is characterized by platelet consumption and profound thrombocytopenia. This distinction is important, as the management of these two conditions is different (46). While thought to be rare, case reports of thromboembolic complications from VMs have been reported (47,48,49). Increasing age, larger extent of malformation, and palpable phleboliths have been shown to be risk factors for thromboembolic complications (49,50). As with the patient above, phleboliths can be present in VMs, and are palpated on physical exam as hardened nodules. They occur because of intravascular thrombi which calcify over time, and can be exquisitely painful (19).