With giant hemangiomas in small children, thrombocytopenia and red cell changes compatible with trauma ('microangiopathic hemolytic anemia') have been observed. The mechanism of the hematologic changes is obscure. No evidence of a simple genetic basis has been discovered.
Propp and Scharfman (1966) reported a male infant with thrombocytopenia associated with a large hemangioma of the right arm and axilla. The patient had low platelet counts with a markedly diminished platelet survival time and an absence of platelet agglutinin or complement-fixing antibody. Radiochromate-tagged platelet studies suggested sequestration in the hemangioma, liver, and spleen. A combination of reticulocytosis and helmet cells was observed, possibly indicating an associated microangiopathic hemolytic anemia. The hemangioma eventually regressed with radiotherapy.
David et al. (1983) reported 2 unrelated infants with thrombocytopenia and hemangiomas of the neck and left knee, respectively, both of whom were treated with corticosteroids without notable improvement. The hemangioma of the knee ultimately showed slow spontaneous resolution, but the cervical hemangioma required radiotherapy.
Larsen et al. (1987) reported their 15-year experience managing 6 children with capillary hemangiomas associated with consumptive coagulopathy. In 3 of their patients, the hemangiomas remained small for many months and then suddenly enlarged, with the simultaneous appearance of a hemorrhagic diathesis. The duration of the thrombocytopenia ranged from 5 to 20 months; a variety of therapies were used. All of the patients eventually experienced resolution of their lesions and a concomitant reversal of the coagulopathy.
Sencer et al. (1987) reported the case of a newborn infant with splenic hemangioendothelioma with thrombocytopenia, anemia, and disseminated intravascular coagulation who was successfully treated with splenectomy.
Vellodi and Bini (1988) described a severe hyperkalemia resulting in 'malignant ventricular arrhythmias.' They attributed the hyperkalemia to breakdown of erythrocytes. Breakdown of platelets is another possible source.
Enjolras et al. (1997) examined biopsy specimens from 15 patients with KMS and concluded that the vascular lesion underlying KMS is not a 'true,' classic, involuting type of hemangioma of infancy. It is a different vascular tumor with a resemblance pathologically to either tufted angioma or kaposiform hemangioendothelioma in association with lymphatic-like vessels. Enjolras et al. (1997) noted that in KMS, when cessation of platelet consumption is achieved, the tumoral mass rapidly resolves and the patient enters a biologic and clinical remission. Thus, in KMS it appears not only that the vascular anomaly triggers platelet trapping and consumption but that platelet activation inside these lesions sustains the growth of a cellular tumor component.
Szlachetka (1998) reviewed the approximately 205 reported cases of KMS and discussed the pathophysiology, clinical manifestations, differential diagnosis, and treatment modalities of the disorder.Animal Model
In a mouse model of Kasabach-Merritt syndrome, Verheul et al. (1999) stimulated platelet production using Peg-rHuMGDF and observed a 7- to 8-fold increase in platelet counts and a significantly increased survival, with 50% of treated animals alive at 1 month versus none of the untreated controls. There was also inhibition of tumor growth by 75%; histologic examination revealed fresh fibrin clot in the treated tumors, suggesting that higher platelet counts caused intravascular thrombosis of tumor vessels. Verheul et al. (1999) concluded that increased platelet production in this model of KMS resulted in an antivascular tumor effect via platelet trapping.