Infants with Kasabach-Merritt syndrome do not have ''true'' hemangiomas

Objective: In 1940 Kasabach and Merritt described an infant with a vascular anomaly, extensive purpura, and thrombocytopenia; they called his lesion ''capillary hemangioma.'' Hemangioma is a benign tumor that grows in infancy and is characterized by proliferation of endothelial cells and regression during childhood, Although Kasabach-Merritt syndrome (KMS) is frequently mentioned as a possible complication of hemangioma, our experience suggests that the anatomic vascular lesion underlying the thrombocytopenia is not a ''true,'' classic, involuting type of hemangioma of infancy and childhood. Study design: We reviewed the clinical and hemostasis data and the response to treatment in 22 cases of KMS, and we analyzed the biopsy specimens of 15 of them, Results: Clinically none of the 22 patients had classic hemangioma. There was no female preponderance. All patients had severe thrombocytopenia (lowest platelet count = 3000/mm(3)) and consumption of fibrinogen. Histologically, none had the typical ''capillary,'' involuting type of hemangioma of infancy: they exhibited either a tufted angioma or a kaposiform hemangioendothelioma pattern; all specimens also contained numerous abnormal lymphatic-like vessels; lymphatic malformation was the major component in two patients, The infants exhibited a heterogeneous response to a number of therapeutic regimens, as noted in other reports. Severe morbidity was present; three of our patients died, and one had leg amputation. ''Residua'' were, in fact, residual vascular neoplasia, variable in duration, and not a stable fibrofatty residuum, as in classic involuted hemangioma; only the hematologic phenomenon was ''cured'' after a period of years, Conclusions: KMS is a distinctive disease of infancy, but the underlying vascular lesion is not a ''true,'' classic, involuting type of hemangioma of infancy, This is a different vascular tumor with a resemblance pathologically to either tufted angioma or kaposiform hemangioendothelioma in association with lymphatic-like vessels, Whether the underlying lesion in KMS is a single anatomic entity or heterogeneous cannot be definitely concluded from this study, We need a better understanding of the pathogenesis of KMS to improve our therapeutic management.