Infantile Hemangioendothelioma IHE

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IHE is the most common benign liver tumor in children. It is a vascular tumor derived from endothelial cells that proliferate and form vascular channels. IHE is relatively common and accounts for 10-15% of all childhood hepatic tumors [24]. Ninety percent of IHE are discovered within the first six months of life and females are affected more than males.

IHE are usually multiple or diffuse; a solitary lesion is an uncommon variant [59]. The nodules vary from a few millimeters to 15 cm or more in size. Typically, they are round, red-brown and spongy or white-yellow with fibrotic predominance in mature cases [82]. Microscopically, IHE represent a proliferation of small vascular channels lined by endothelial cells. Cavernous areas, as well as foci of hemorrhage, thrombosis, fibrosis and calcification, are common. The multinodular type may also involve other organs, as well as the skin [43].

Clinical findings, if present, may include hepatomegaly, congestive heart failure, thrombocy-topenia caused by the trapping of platelets by the tumor (Kasabach-Meritt syndrome), and occasionally rupture with hemoperitoneum [53]. In symptomatic cases, as often occurs with the diffuse form (Fig. 1), treatment modalities include steroid administration, chemo- and radiotherapy, embolization or ligation of the hepatic artery and resection.

The natural history of IHE is benign, and lesions tend to regress gradually over a period of

Fig. 1a-e. Diffuse form of infantile hemangioendothelioma. On the respiratory gated T2-weighted TSE image (a) multiple high SI lesions throughout the liver can be observed. The corresponding T1-weighted image (b) reveals some larger vessels with flow void (arrowheads) that clearly supply one of the lesions (arrow). On the dynamic study following contrast agent injection (c, d), early and strong enhancement of the lesions occurs during the arterial phase (c), which persists into the portal venous phase (d). Persistent enhancement is also seen on the Tl-weighted fat-suppressed image acquired in the equilibrium phase (e), which points to a diagnosis of multiple vascular tumors. Due to heart insufficiency caused by the shunt flow from multiple hemangioendothelioma, steroid administration was performed and most of the lesions disappeared within 6 weeks of treatment

Fig. 1a-e. Diffuse form of infantile hemangioendothelioma. On the respiratory gated T2-weighted TSE image (a) multiple high SI lesions throughout the liver can be observed. The corresponding T1-weighted image (b) reveals some larger vessels with flow void (arrowheads) that clearly supply one of the lesions (arrow). On the dynamic study following contrast agent injection (c, d), early and strong enhancement of the lesions occurs during the arterial phase (c), which persists into the portal venous phase (d). Persistent enhancement is also seen on the Tl-weighted fat-suppressed image acquired in the equilibrium phase (e), which points to a diagnosis of multiple vascular tumors. Due to heart insufficiency caused by the shunt flow from multiple hemangioendothelioma, steroid administration was performed and most of the lesions disappeared within 6 weeks of treatment months [72]. However, malignant transformation of IHE into angiosarcoma may occur on rare occasions.

The ultrasonographic features of IHE are varied. Typically, there is a complex liver mass with large, draining hepatic veins [101]. Single or multiple lesions may be seen, and the lesions may range from hypoechoic to hyperechoic. These lesions may involute slowly over a period of months and develop increased echogenicity [21,72].

On unenhanced CT examinations, IHE appear as hypodense masses with or without calcifications [74]. Early enhancement of the edge of the mass with variable delayed central enhancement is usually seen after administration of contrast medium [74].

Vascular channels and cyst-like components, which are usually well-defined, determine the hy-pointensity of the lesions on unenhanced T1-weighted Mr images. On T2-weighted images the lesions usually appear homogeneously hyperin-tense, although some hypointense areas indicative of hemorrhage, thrombosis, fibrosis or calcification may be present (Fig. 2). After contrast agent administration, intense, peripheral enhancement or, less frequently, globular enhancement may be seen. Complete or incomplete filling-in during the portal-venous and equilibrium phases is also observed. On delayed phase images after Gd-BOPTA, IHE tend to be iso- or hypointense compared to the surrounding liver parenchyma (Fig. 3) [69,72].

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