Leiomyosarcoma Malignant Fibrous Histiocytoma and Fibrosarcoma

These neoplasms are very rare tumors of the liver which usually occur in patients between 40 and 60 years of age, without gender predilection. Leiomyosarcoma is the most common of these lesions but to date only 54 cases have been described in the literature [29]. Microscopically, leiomyosarcomas originate from mesenchymal elements of the liver, and are composed of large smooth muscle spindle cells. Malignant fibrous histiocytoma was first described as a separate pathologic entity in the 1960s and 1970s. This lesion is composed of primitive cells that demonstrate partial histiocytic and fibroblastic differentiation. Finally, fibrosarco-ma is a malignant tumor of soft tissue that is composed of undifferentiated cells derived from collagen-producing fibroblasts [42,23]. Macroscopical-ly, each of these lesions appears as a large, typically solitary mass in a non-cirrhotic liver. Sometimes it is possible to find necrotic and hemorrhagic areas.

On US these neoplasms appear as large, solid, and well-defined masses, with variable echo patterns depending on the degree of hemorrhage and necrosis. On CT, they appear as well-defined slightly hypodense, heterogeneous masses before contrast medium administration, and show progres-

Fig. 37a-f. Angiosarcoma. The unenhanced T2-weighted image (a) reveals a high signal intensity mass with hypointense areas that represent large vessels with flow void (arrows). The signal intensity of the lesion is comparable to that seen with hemangioma. On the corresponding unenhanced T1-weighted gradient echo image (b), the mass is again sharply demarcated and shows homogeneous signal intensity. In contrast to hemangioma, enhancement is seen in central areas of the lesion on arterial phase images (c) with subsequent centrifugal filling-in of the lesion in the portal-venous phase (d). The peripheral areas of the lesion still do not show enhancement on T1-weighted images acquired 5 min after contrast agent injection (e) (arrows). However, by 10 min after contrast agent administration (f) homogeneous enhancement of the lesion can be observed, comparable to a hemangioma. The clue for diagnosis in this case is the centrifugal enhancement in the lesion rather than the nodular peripheral enhancement typically observed in hemangioma

Fig. 37a-f. Angiosarcoma. The unenhanced T2-weighted image (a) reveals a high signal intensity mass with hypointense areas that represent large vessels with flow void (arrows). The signal intensity of the lesion is comparable to that seen with hemangioma. On the corresponding unenhanced T1-weighted gradient echo image (b), the mass is again sharply demarcated and shows homogeneous signal intensity. In contrast to hemangioma, enhancement is seen in central areas of the lesion on arterial phase images (c) with subsequent centrifugal filling-in of the lesion in the portal-venous phase (d). The peripheral areas of the lesion still do not show enhancement on T1-weighted images acquired 5 min after contrast agent injection (e) (arrows). However, by 10 min after contrast agent administration (f) homogeneous enhancement of the lesion can be observed, comparable to a hemangioma. The clue for diagnosis in this case is the centrifugal enhancement in the lesion rather than the nodular peripheral enhancement typically observed in hemangioma sive enhancement after contrast medium administration which is more evident in the equilibrium phase. Areas of necrosis and hemorrhage are non-enhancing on post-contrast CT images.

These lesions demonstrate inconsistent signal intensity on pre-contrast T2- and T1-weighted MR images although frequently the signal is slightly hyperintense on T2-weighted images and hy-pointense on T1-weighted images compared with normal liver parenchyma. Typically, internal, hy-perintense areas which correspond to necrosis and acute or subacute hemorrhage can be seen. After contrast agent administration, these neoplasms show a slight but often homogeneous enhancement compared to the surrounding normal liver parenchyma [65,83].

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