Approach Considerations
Any infant with unexplained thrombocytopenia, with or without evidence of disseminated intravascular coagulation (DIC), should be evaluated for visceral or hidden vascular lesions (especially of the spleen). Without prompt and appropriate attention, these forms of Kasabach-Merritt syndrome (KMS) are associated with a high mortality. Patients should also be evaluated for malignancy because malignant lesions may resemble the lesions seen in patients with KMS.
Clinicians must monitor blood work, with special emphasis on the platelet count. Additional tests are ordered as necessary for clinical evaluation. For example, blood cultures may be appropriate for excluding the possibility of sepsis, and chromosome tests may be needed to exclude certain genetic syndromes.
Diagnostic imaging is obtained as appropriate. No procedures are required initially. If a complete excision is not feasible, a biopsy should not be performed, because it may lead to uncontrolled bleeding at the site.
Although formal staging is not usually performed, documenting the extent of the invasion of the vascular lesion into normal tissue is important for possible subsequent treatment with surgery or radiation. Metastasis does not occur.
Laboratory Studies
A complete blood count (CBC) with differential, reticulocyte count, platelet count, and peripheral smear is obtained to evaluate for microangiopathic hemolytic anemia and thrombocytopenia in KMS. Platelets may be larger than normal when they are released early from the bone marrow. Burr cells and schistocytes may be present in patients with microangiopathic hemolytic anemia.
The prothrombin time (PT) and activated partial thromboplastin time (aPTT) are prolonged in patients with significant DIC.
Fibrinogen levels are low in patients with significant DIC. levels of fibrin degradation products (FDPs) and D-dimer are elevated in patients with DIC. A D-dimer test is usually more sensitive than a test for FDPs. Low-grade chronic DIC may be present.
Radiography, CT, MRI, and Ultrasonography
Radiography, computed tomography (CT), and magnetic resonance imaging (MRI) of areas involved with known vascular lesions should be performed as appropriate. These studies are advisable even when all vascular lesions are cutaneous. Scans are important to determine the extent of the visible vascular lesions and to evaluate the patient for possible visceral vascular lesions.
MRI or CT commonly reveals a vascular enhancing mass that is difficult to differentiate from a vascular malformation, solid tumor, or proliferative vascular lesion. If KMS is suspected in patients who have no visible vascular lesions, CT scans or MRIs of the head, chest, abdomen, and pelvis should be obtained to identify any visceral lesions.
A study by Gong et al found that on MRI, kaposiform hemangioendotheliomas have a greater tendency than tufted angiomas to display diffuse heterogeneous enhancement with the use of contrast. [19]
Doppler flow studies may help differentiate a solid mass from a vascular lesion. The aforementioned study by Gong et al identified ultrasonographic differences that can aid in distinguishing a kaposiform hemangioendothelioma from a tufted angioma. The investigators determined, for example, that compared with tufted angiomas, kaposiform hemangioendotheliomas in the report had greater depth and vascular density and were harder on elastography. Moreover, kaposiform hemangioendotheliomas that were specifically associated with KMS had a significantly higher arterial peak systolic blood flow velocity than did tufted angiomas and non-KMS kaposiform hemangioendotheliomas. The study also found that on three-dimensional (3-D) color Doppler, kaposiform hemangioendotheliomas had a branch-shaped blood flow, compared with a dot-like and striped pattern for the tufted angiomas. [19]
Radionuclide Scanning
Radionuclide imaging may be indicated. Scans that use chromium isotope 51, indium In 111 oxine–labeled platelets, or iodine I 131–labeled fibrinogen probably are more sensitive than CT scans or MRIs for delineating the size and number of vascular lesions. [20] Radionuclide scans are infrequently used because the diagnosis is usually made clinically. In certain centers, they may not be readily available. Scintigraphic studies should be strongly considered when the etiology of the thrombocytopenia remains uncertain.
Histologic Findings
Enjolras et al characterized the histology of kaposiform hemangioendothelioma (KHE) and tufted angioma (TA), the vascular lesions associated with KMS. [9] The original case report described lobules of fine capillaries separated by cellular intercapillary tissue consisting of spindle-shaped cells.
The histologic picture of KHE consists of lobules or sheets of tightly packed spindle cells or rounded endothelial cells and pericytes. The cellular areas have an infiltrative pattern in the dermis, subcutaneous fat, and muscles and generally contain few obvious vascular lumina. TAs are composed of small tufts or lobules of rounded capillaries with small lumina. The tufts are discrete and evenly distributed in a cannonball pattern and are characterized by peripheral, crescentic, slitlike vessels and an associated fibrosis.
Both KHE and TA contain aggregates of rounded, dilated capillaries lined by attenuated endothelial cells with small, dark nuclei and filled with RBCs. Microthrombi and hemosiderin deposits are often present. Lymphlike vessels are often part of the lesion. Findings of both KHE and TA often appear in the same patient; the 2 conditions may be variations of each another.
The histology of classic hemangioma of infancy, which is the most common benign vascular neoplasm in children, is distinct from these proliferations and is not associated with KMS.
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Leg with a Kaposiform hemangioendothelioma, lesion associated with Kasabach-Merritt Syndrome.
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Back of an arm showing the typical bruising associated with Kasabach-Merritt Syndrome.
