Kaposiform hemangioendothelioma complicated by Kasabach-Merritt phenomenon: ultrastructural observation and immunohistochemistry staining reveal the trapping of blood components.

Kaposiform hemangioendothelioma (KHE), a borderline tumor of endothelial origin, is associated with Kasabach-Merritt phenomenon, characterized by profound thrombocytopenia and consumptive coagulopathy resulting from the localized intravascular coagulation (LIC) in the tumor. Previous studies have suggested that the trapping of blood components, including platelets, may underlie the LIC in KHE. However, more evidence is needed to support this hypothesis. In this study, one case of a Chinese infant with a KHE in the left arm was complicated by Kasabach-Merritt phenomenon. The tumor was partially resected and the sample was used for ultrastructural observation and immunohistochemistry staining of Glut-1. Ultrastructural observation found the trapping of erythrocytes, platelets, macrophages, and lymphocytes in the slit-like channels of the tumor nodules, and phagocytic vesicles in the cytoplasm of neoplastic cells. Immunohistochemistry staining further showed numerous Glut-1(+) erythrocytes in the channels. In conclusion, our results provided compelling morphological evidence of the trapping of blood components in KHE, which may interpret the LIC in the tumor and subsequent consumptive coagulopathy.

Primary kaposiform hemangioendothelioma of a long bone: two cases in unusual locations with long-term follow up.

Kaposiform hemangioendothelioma (KHE) is a rare vascular neoplasm of low malignant potential that mainly affects infants and adolescents. The tumor almost exclusively occurs in somatic soft tissue or the retroperitoneum. We report herein two cases of primary KHE occurring in a long bone without cutaneous changes with long-term follow up in young patients. The patients were a 9-year-old girl and 5-year-old boy presenting with lytic lesions of the femur and humerus, respectively, without cutaneous lesions. Histologically, the neoplasms were comprised of nodules of spindle- to oval-shaped cells growing in an infiltrative fashion. The neoplastic cells formed poorly canalized or slit-like blood vessels alternating with solid spindle areas. Immunohistochemical studies showed that the tumor cells expressed CD31, CD34 and Fli1, but not HHV8, LNA-1 or GLUT1. D2-40 stained the neoplastic spindle cells and lymphatic channels adjacent to vascular lobules. The girl remains well with 15 years and 6 months follow up after a second complete excision. The boy has no signs of recurrence or metastasis nearly 5 years after local complete excision. To our best knowledge, this is the first report in the English literature of primary long bone occurrences of KHE without cutaneous changes with long-term follow up.