The Kasabach-Merritt Phenomenon (KMP) is a complication of a rapidly enlarging vascular lesion. Many children with KMP also have:

• Hemolytic anemia (a condition in which red blood cells are destroyed and removed from the bloodstream before their normal lifespan is over)
• Thrombocytopenia (a condition in which the blood has a lower than normal number of platelets, or blood cell fragments)
• Coagulopathy (a disorder in which blood is either too slow or too quick to clot)

Most cases can be seen in the first weeks of life. The vascular tumors that cause KMP are:

• Large
• Deep red-blue in color
• Firm

They also:

• Grow rapidly
• Affect boys and girls equally
• Tend to grow for a longer period of time than most vascular anomalies (two to five years of growth is typical)

Children with true KMP do not have hemangiomas of infancy, but rather other more aggressive vascular tumors.

Kaposiform hemangioendotheliomas and tufted angiomas are the tumors most often associated with this phenomenon. They can be very serious, even fatal, and require aggressive and often a combination of different types of treatments.