THROMBOCYTOPENIC COAGULOPATHY (KASABACH-MERRITT PHENOMENON) IS ASSOCIATED WITH KAPOSIFORM HEMANGIOENDOTHELIOMA AND NOT WITH COMMON INFANTILE HEMANGIOMA

Children with a large vascular tumor and associated Kasabach-Merritt c oagulopathy respond inconsistently to therapy and have a high mortalit y rate. For this reason, we undertook a retrospective study of 21 such patients, and focused on clinical, radiographic, and histopathologic features. The male to female ratio was 1:1.6. Tumor was noted at birth in 50 percent of patients; the remainder appeared throughout infancy. The location was cervicofacial (n = 2), shoulder/upper limb (n = 4), trunk including retroperitoneum (n = 11), and lower limb (n = 4). Thes e tumors grew rapidly to large size and were characterized by cutaneou s purpura, edema, and an advancing ecchymotic margin. In contrast to c ommon hemangioma, magnetic resonance imaging showed diffuse enhancemen t with ill-defined margins, cutaneous thickening, stranding of subcuta neous fat, hemosiderin deposits, and small feeding and draining vessel s. All tumors were Kaposiform hemangioendothelioma (KHE); none were in fantile hemangioma. Light microscopy showed irregular lobules or sheet s of poorly formed, small vascular channels infiltrating and entrappin g normal tissues. Characteristic features included spindle-shaped endo thelial cells, diminished pericytes and mast cells, microthrombi, and hemosiderin deposits. Wide endothelial intercellular gaps and incomple te basement membranes were seen by electron microscopy. Dilated, hyper plastic, lymphaticoid channels were prominent in one tumor.KHE in 14 i nfants was treated with interferon alpha-2a: 6 had accelerated regress ion; 2 had stabilization of growth; and 6 evidenced no response. The m ortality rate was 24 percent (5 of 21); this included three infants wi th retroperitoneal KHE. Kasabach-Merritt phenomenon does not occur wit h common hemangioma. Rather it is associated with the more aggressive KHE and rarely with other vascular neoplasms. Variable response to cur rent pharmacologic therapy underscores our inadequate knowledge of the pathogenesis of thrombocytopenia in KHE.