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

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.

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.

Clinically none of the 22 patients had classic hemangioma. There was no female preponderance. All patients had severe thrombocytopenia (lowest platelet count = 3000/mm3) 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.

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.