The Kasabach-Merritt phenomenon is the association of a rapidly enlarging vascular lesion anywhere on the body (commonly an extremity but also head and neck, thigh, sacrum) with consumptive coagulopathy (low fibrinogen, increased D-dimers) and thrombopaenia because platelets are trapped into the tumor.
The lesion is a vascular tumor made of irregular nodules presenting as a kaposiform haemangioendothelioma (spindle-shaped cells) (active phase) or a tufted angioma (glomerular structure with crescentlike vascular cleft, before the active phase or during the regression phase) pattern and with some accompanying lymphangiomatosis at histology.
On the contrary from infantile haemangiomas (common vascular malformation) the endothelial cells lining the lesion are negative for the glucose-transporter-1 (GLUT-1) isoform and for the Lewis Y (LeY) antigen. KHE shows
Careful surgical excision is performed when feasible but the lesion is often extensive, and a medical treatment is necessary: it includes high-dose steroids, vincristine, α- or β- interferon and platelets antiaggregants such as ticlopidine and/or aspirin.
Platelet transfusion is best avoided because it generally results in enlarging the lesion and worsening the coagulopathy because of platelet trapping into the tumor.
The lesion usually appears during the first year of life. Mortality is around 10%.