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).