Kaposiform Hemangioendothelioma and Tufted Angioma

(with or without Kasabach-Merritt syndrome)

Note! Kasabach–Merritt syndrome (KMS), also known as Hemangioma with thrombocytopenia is a rare disease, usually of infants, in which a vascular tumor leads to decreased platelet counts and sometimes other bleeding problems, which can be life-threatening. It is also known as hemangioma thrombocytopenia syndrome. It is named after Haig Haig Uni Kasabach and Katharine Krom Merritt, the two pediatricians who first described the condition in 1940.

Kasabach-Merritt phenomenon occurs with more aggressive and invasive vascular tumors such as kaposiform hemangioendothelioma (KHE), kaposiform lymphatic anomaly (KLA), and tufted angioma (TA).

These tumors are biologically distinct from infantile hemangioma. KHE and TA share several features and are more invasive than hemangioma. They are usually present at birth, but can appear postnatally. They are solitary and, unlike hemangioma, affect males and females equally. They most commonly occur on the trunk, shoulder, thigh, or retroperitoneum. The skin overlying KHE appears purple, tense, and shiny (Image 9.4). In addition, petechiae and ecchymosis surround the tumor.

Generalized petechiae may be apparent due to profound thrombocytopenia (< 10,000 platelets/µL). Infants with Kasabach-Merritt phenomenon are at risk for intracranial, pleural, pulmonary, peritoneal, and GI hemorrhage.

TA appears as an erythematous macule or plaque. A hallmark of these tumors is that they are associated with Kasabach-Merritt syndrome, which is the associated finding of profound thrombocytopenia, petechiae, and bleeding, with large vascular lesions.

If the diagnosis cannot be established based on history and exam, MRI can differentiate KHE from hemangioma. Like proliferating hemangioma, KHE shows enhancement and large vessels on T2-weighted images. However, KHE has poorly defined margins, small vessels, and invasion of adjacent tissues.

Histologically, KHE shows infiltrating sheets or nodules of endothelial cells lining capillaries. In addition, dilated lymphatics are present and filled with hemosiderin and red blood cell fragments. TA may be distinguished from KHE because TA is characterized by small tufts of capillaries (cannonballs) in the middle to lower third of the dermis.

KHE and TA continue to proliferate into early childhood and then partially regress by midchildhood. These lesions usually persist long term, although they are commonly asymptomatic. Systemic corticosteroid is the first-line therapy, followed by interferon. However, only 50% of these lesions respond to pharmacologic treatment and mortality rates are high (20% to 30%). Platelet transfusions should be avoided unless there is active bleeding or a planned surgical procedure because exogenous platelets are trapped in the lesion causing swelling. In addition, heparin should not be administered because it stimulates tumor growth and aggravates platelet trapping, worsening bleeding.

Other treatment alternatives for patients with KHE are transcatheter embolization and surgical excision.