Undifferentiated Embryonal Sarcoma UES

UES was first recognized as a clinical pathological entity in 1978 [93]. This neoplasm had previously been attributed various terms, including embryonal sarcoma, primary sarcoma, fibromyxosarcoma, and malignant mesenchymoma. Although rare, UES is the fourth most frequent hepatic neoplasm in infancy after HB, hemangioendothelioma and HCC.

UES occurs predominantly in children between six and ten years of age [22], although it has also been known to affect adults [9]. The incidence is almost the same in males and females [25,47,52].

Histologically, UES is composed of undifferen-tiated fusiform cells resembling primitive embry onal cells, and myxoid stroma [38]. A relationship has been suggested between UES and mesenchy-mal hamartoma [23]. However, these two neoplasms are distinguished not only by their histology, but also by their time of onset and clinical presentation: mesenchymal hamartoma is typically observed in small children, aged between four months and two years, whereas UES occurs in older children. Moreover, whereas the former is symptom-free, UES is usually symptomatic [25].

Macroscopically, UES presents as a large mass, located more frequently in the right lobe of the liver. It is often well-defined and sometimes complete with a pseudo capsule; it can reach 20 cm in diameter and may contain cystic, hemorrhagic and/or necrotic areas, as well as having a cellular component. The cystic variants are more frequent than the solid forms and reflect the rapid growth of the neoplasm [64,81].

UES frequently presents as a palpable abdominal mass with or without pain, fever, jaundice and weight loss [25, 64, 89]. Sometimes, the tumor may rupture, leading to acute abdominal crisis [82]. There are no reliable changes in laboratory data, although mild leukocytosis and anemia may be seen in 50% of cases and elevated liver enzymes in 30% of cases. Typically, serum AFP levels are normal [20,99].

In cases of UES, the prognosis depends on the possibility of achieving complete resection of the neoplasm. Although this is often difficult, when combined with adjuvant chemotherapy it offers the best chance of cure [99,100].

On US this neoplasm can present either as a hy-poechogenic mass with multiple hyperechogenic septa of variable thickness, or as an echogenic lesion containing numerous small cystic collections. This diversity of echostructure depends on the greater or lesser prevalence of the myxoid, solid, and hemorrhagic or necrotic components [9, 41, 64,81,89].

At CT imaging, UES generally presents as a large intrahepatic mass that has lower attenuation than the surrounding liver parenchyma. The abundant myxoid matrix of the tumor may be the cause of the hypodense appearance on CT. Conversely, lesions with higher-density contain hemorrhagic, necrotic or solid material. In some cases, a dense, peripheral enhancing thin rim corresponding to the fibrous pseudocapsule may be depicted on CT images. Likewise, hyperdense septations may also be seen in some cases [64,81].

The MR findings are related to the cystic degeneration and the hemorrhagic-necrotic components of the tumor. On unenhanced T1-weighted images the neoplasm is typically hypointense due to cystic degeneration, with areas of higher SI reflecting hemorrhagic events. On T2-weighted images the SI reflects the cystic or solid predomi-

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Fig. 14a, b. Undifferentiated embryonal sarcoma. On the unenhanced T1-weighted image (a), a large cystic septated lesion (asterisk) involving a large part of the liver can be seen. On the coronal T2-weighted image (b), the mass appears hyperintense and multiloculated nance of the lesion, with marked signal hyperin-tensity in the case of a cystic lesion (Fig. 14). The fibrous pseudocapsule and septations, if present, are typically hypointense on both T1- and T2-weighted images [10,81,89,105].

Catheter angiography generally reveals a hypo-or avascularized neoplasm and the extent of vas-cularization is inversely proportional to the cystic transformation. There are signs of macro-aneurysms, arterio-venous shunts, and stasis of the contrast medium in the solid portion of the tumor. Though these angiographic aspects are nonspecific, the macro-aneurysms observed in the vascularization of the neoplasm have not been reported in any other hepatic malignancies, apart from UES [105].

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