Epithelioid Hemangioendothelioma

Epithelioid hemangioendothelioma (EHE) is a rare malignant hepatic neoplasm of vascular origin that develops in adults. It is more common in women than in men. No risk factors or specific causes have been identified [102].

Macroscopically, two different types of EHE have been described [27]. The nodular type represents an early manifestation of the disease. In the majority of cases there are multiple nodular lesions ranging in size from 1 to a maximum of 3 cm. Frequently, the nodules are found in both lobes of the liver and are located at sub-capsular sites in 50 to 65% of cases. Lesions adjacent to the capsule often cause capsular retraction [27]. The diffuse type of EHE develops in the later stages of the disease. It originates from the nodular type, with the nodules increasing in size until they finally coalesce, forming extensive peripheral lesions [67]. The route of lesion spread follows the hepatic veins or the different branches of the portal vein [26].

Histologically, EHE is composed of fibrous myxoid stroma with a relatively hypocellular center and two cell types: epithelioid and dendritic. The epithelioid cells stain positive for factor VIII-

related antigen, indicating the vascular nature of this neoplasm which distinguishes it from metastasis. Intratumoral necrosis and hemorrhage are common [67].

The clinical manifestations are non-specific and variable, ranging from the complete absence of symptoms to hepatic failure. When present, the typical symptoms include right upper quadrant or epigastric discomfort or pain, weight loss, and weakness. Less common symptoms at initial presentation include jaundice, fever, and tiredness. Raised levels of serum alkaline phosphatase (AP) are found in approximately 70% of patients. Occasionally, rupture with hemoperitoneum may be present [41, 58]. Hepatomegaly and abdominal pain are present in 50 to 70% of cases.

On US, EHE is usually well-defined and hypoe-choic, although hyperechoic examples are occasionally seen. Sometimes it is possible to find hy-poechoic and hyperechoic lesions with a peripheral hypoechoic rim in the same patient (Fig. 33) [67]. Echo-color Doppler may show vasculariza-tion within the nodule. When the lesions appear hyperechoic, differential diagnosis with heman-gioma is possible; capsular retraction in EHE, which is commonly not observed in hemangioma, is another important feature for differential diagnosis.

Eus And Hyperechoic Liver Lesions
Fig. 33a-c. Epithelioid hemangioendothelioma on US. Ultrasound reveals an isolated well-defined hypoechoic lesion (asterisk) (a), numerous well-delimited hyper-echoic nodules (arrows) (b), or hypoechoic and hyperechoic lesions (arrowheads) with peripheral hypoechoic rims (c)

On unenhanced CT images, the nodular type of EHE is of low attenuation, corresponding to myx-oid stroma. After intravenous administration of contrast material, areas of high density can be observed in the periphery of the tumor, however, the center of the tumor shows very few or no contrast-enhancing areas [11,67,100]. In the diffuse type of EHE, CT scans reveal large, hypodense, diffuse areas throughout the liver extending toward the periphery. The outline is usually irregularly shaped. Focal calcifications within the tumor are found in about 20% of cases. Compensatory hypertrophy of unaffected liver segments, as well as splenomegaly, are common findings. The liver capsule is not usually affected, although confluent nodules may produce capsular retraction (Fig. 34). After intravenous administration of contrast material, enhancement at the periphery of the tumor can be observed, corresponding to a proliferating zone of active growth. Hypervascular areas, indicative of the vasoformative structure of the tumor or of a more distinct representation of blood vessels due to an obstruction of the portal vein, can sometimes be detected within the tumor [67,100]. The tumor itself takes up only a small amount of con trast medium. During the delayed phase, the tumor becomes increasingly isodense, which makes it difficult to distinguish from normal liver tissue. Slightly ill-defined areas can be seen in the delayed phase (Fig. 35). However, the extension of the tumor is often better defined on unenhanced CT images [11].

The MR imaging features of EHE are similar to the CT findings: either peripheral nodules or larger confluent lesions are seen. The tumors are hy-pointense on T1-weighted images and hyperin-tense on T2-weighted images, although a hy-pointense center corresponding to calcification, necrosis and hemorrhage may be seen on both sequences. After intravenous administration of ex-tracellularly distributed contrast material, moderate peripheral enhancement, progressive filling-in and delayed central enhancement can usually be seen, particularly in larger lesions. Peripheral wash-out can also be seen, which is useful for characterization. Lesions are generally seen as hy-pointense on delayed hepatobiliary phase images, compared to the surrounding liver parenchyma and to pre-contrast images after the administration of Gd-BOPTA (Fig. 36) [100].

Fig. 34a-d. Epithelioid hemangioendothelioma on CT. Unenhanced CT (a) reveals large hypodense, confluent diffuse nodules (asterisks). Arterial (b) and portal-venous (c) phase images acquired after the administration of contrast material reveal enhancement at the periphery of the nodules but few contrast-enhancing areas at the center of the lesions. In the equilibrium phase (d) the nodules become hetero-geneously hyperdense compared to normal liver, while compensatory hypertrophy and capsular retraction can be clearly seen

Fig. 34a-d. Epithelioid hemangioendothelioma on CT. Unenhanced CT (a) reveals large hypodense, confluent diffuse nodules (asterisks). Arterial (b) and portal-venous (c) phase images acquired after the administration of contrast material reveal enhancement at the periphery of the nodules but few contrast-enhancing areas at the center of the lesions. In the equilibrium phase (d) the nodules become hetero-geneously hyperdense compared to normal liver, while compensatory hypertrophy and capsular retraction can be clearly seen

Hemangioendothelioma Ultrasound Images

Fig. 35a-d. Epithelioid hemangioendothelioma (diffuse type). On unenhanced CT (a) several hypodense peripheral nodules (arrowheads) can be seen; several of these lesions show central calcification. Dynamic evaluation of these lesions after administration of contrast material reveals peripheral enhancement in the early post-contrast phases (b and c) but isodensity with the normal parenchyma on images acquired in the equilibrium phase (d)

Fig. 36a-f. Epithelioid hemangioendothelioma. This figure shows the same case as Fig. 35. The lesions (arrowheads) are seen as hyper-intense and hypointense on unenhanced T2-weighted (a) and T1-weighted (b) images, respectively. Peripheral enhancement and progressive filling-in of the lesions are seen on arterial (c) and portal-venous (d) phase images after the bolus injection of Gd-BOPTA. In the equilibrium phase (e) the lesions are seen as either completely or incompletely hyperintense against the normal parenchyma. Images acquired during the delayed hepatobiliary phase (f) show the lesions to be homogeneously hypointense compared to the normal liver

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Fig. 36a-f. Epithelioid hemangioendothelioma. This figure shows the same case as Fig. 35. The lesions (arrowheads) are seen as hyper-intense and hypointense on unenhanced T2-weighted (a) and T1-weighted (b) images, respectively. Peripheral enhancement and progressive filling-in of the lesions are seen on arterial (c) and portal-venous (d) phase images after the bolus injection of Gd-BOPTA. In the equilibrium phase (e) the lesions are seen as either completely or incompletely hyperintense against the normal parenchyma. Images acquired during the delayed hepatobiliary phase (f) show the lesions to be homogeneously hypointense compared to the normal liver

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