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Malignant Neoplasms 4.1.6.2.1

Hepatoblastoma

Hepatoblastoma is the third most common intraabdominal malignancy (after neuroblastoma and Wilms tumour) in children. Almost all patients with hepatoblastoma are younger than 3 years, with a peak presentation at between 18 and 24 months. With an overall incidence of 1 per million, premature children with extremely low birth weight and long hospitalization have a higher risk for hepatoblas-toma with a poor prognosis; these patients should be screened with abdominal US and serum alpha-fetoprotein early in life. Beckwith-Wiedemann syndrome, trisomy 18, familial adenomatous polyposis, Gardner's syndrome, and glycogen storage disease have been associated with increased risk of hepatoblastoma. Unlike hepatocellular carcinoma, hepatoblastoma has no association with cirrhosis (Oue et al. 2003; DACHmAN et al. 1987).

Typically, a hepatoblastoma will present with hepatomegaly. Increased levels of alpha-fetoprotein will be present in 90% of cases and will be helpful in following the patient. Weight loss, fever, and loss of appetite are other symptoms. When metastases occur, the lungs and regional lymph nodes are commonly involved, but also the skeleton, ovaries, brain, and eyes.

Abdominal radiography may show hepatomegaly as evidenced by elevation ofthe right hemidiaphragm and displacement of intraluminal air by an enlarged liver (Fig. 4.9a). Although not diagnostically specific, coarse, stippled and solid hepatic calcifications may be present in the right upper quadrant. Chest radiography may demonstrate pulmonary metastases and can aid in the differential diagnosis. Plain films cannot localize the tumor to the liver definitively, distinguish between the solid or cystic nature of a neoplasm, or provide information regarding tumor vascularity (Kuhn et al. 2004).

An hepatoblastoma can present as a solitary mass, with or without satellite lesion or as multiple nodules throughout the liver (Roebuck 2006). On US, hepatoblastoma presents as a mass with ill-defined borders, and heterogeneous echogenicity, showing slightly more echogenic areas compared to the surrounding parenchyma and anechoic areas that correspond to necrosis or hemorrhage. Calcifications can also be present (Fig. 4.9b).

Visualization and evaluation of intrahepatic vascular structures is important because hepatoblas-tomas can invade or compress the portal and the hepatic veins. Absence of the portal branch or presence of a thrombus supports portal vein invasion. Although the inferior vena cava can be invaded, US examination overestimates the incidence of obliteration of this vessel (SiEgEL 2001a; Kuhn et al. 2004).

Sulfur-colloid liver scintigraphy may show large filling defects in the hepatic parenchyma, with prominent tracer avidity at the site of the tumor within a few seconds of the appearance of the bolus in the abdominal aorta. This increased activity persists into the venous phase. Hepatoblastomas may demonstrate increased uptake on delayed imaging, but this is rare (SuCHy 2003).

On CT, the appearance of hepatoblastoma varies greatly. Prior to contrast administration, the tumor may appear as a, or multiple, homogeneous hypodense mass(es) (epithelial-type tumor); however, it may demonstrate a more heterogeneous appearance (mixed mesenchymal-epithelial tumor), corresponding to areas of necrosis or hemorrhage (Fig. 4.9c-g). Vascular compression and tumor extension is also well assessed. Calcifications may be present and follow-up CT after chemotherapy may

Fig. 4.8a-g. Focal nodular hyperplasia. a Area of decreased echogenicity in the left lobe ofthe liver (asterisk). b Enlarged view of (a) (arrowheads). c Low Doppler signal. d Arterial Doppler signal of same. e CT liver demonstrates enhancing of the lesion. f MR of FNH (arrows). g Pooling of contrast agent in FNH (arrows)

Fig. 4.8a-g. Focal nodular hyperplasia. a Area of decreased echogenicity in the left lobe ofthe liver (asterisk). b Enlarged view of (a) (arrowheads). c Low Doppler signal. d Arterial Doppler signal of same. e CT liver demonstrates enhancing of the lesion. f MR of FNH (arrows). g Pooling of contrast agent in FNH (arrows)

Fig. 4.9a-g. Hepatoblastoma. a Plain film demonstrates hepatomegaly and multiple round lesions in the chest. Patient with hepatoblastoma in which (b1): US shows highly echogenic lesion posteriorly in the liver; scar may be visible; and (b2): MR image of same, in the coronal plane. c-e CT of the abdomen depicts heterogeneous enhancement of multiple lesions, with tumor extension into the IVC (arrow). f,g CT of chest reveals multiple metastatic lesions f

Fig. 4.9a-g. Hepatoblastoma. a Plain film demonstrates hepatomegaly and multiple round lesions in the chest. Patient with hepatoblastoma in which (b1): US shows highly echogenic lesion posteriorly in the liver; scar may be visible; and (b2): MR image of same, in the coronal plane. c-e CT of the abdomen depicts heterogeneous enhancement of multiple lesions, with tumor extension into the IVC (arrow). f,g CT of chest reveals multiple metastatic lesions d e g show an increase in these calcifications as a normal finding (Kirks and Griscom 1998).

Following the injection of IV contrast, hepato-blastomas may demonstrate an inhomogeneous enhancement pattern, usually with a higher density compared to the surrounding liver parenchyma. A peripheral rim of enhancement, which corresponds to compressed parenchyma may be observed if imaging is performed during the early arterial phase. If peripheral enhancement is seen, delayed serial scans at a single level of the tumor can be performed to distinguish hepatoblastoma from heman-gioendothelioma.

On MRI, hepatoblastoma will have low signal intensity on T1-weighted images, and heterogeneous high signal intensity on T2. Sometimes high signal lesions can be seen on T1-weighted images and represent hemorrhage. Hypointense bands on T1- and T2-weighted images might also be seen and will correspond to fibrotic tissue. However, MRI has been used more in the evaluation of tumor extension, vascular compression, and complications than for diagnosis. In the evaluation of parenchymal extension of the tumor and lymph node infiltration, MRI, and STIR sequences in particular, have proved to be a useful tool. Although STIR is very effective in determining abnormal abdominal nodes, it cannot differentiate between reactive lymph node versus malignant infiltration (Kirks and Griscom 1998).

Evaluation of the hepatic vasculature is essential before tumor resection. MRI or CT can show vascular involvement even without contrast enhancement. Other modalities such as 3D MRA have been used for this purpose, with the advantage that the images can be studied in both the arterial and venous phases (Haliloglu et al. 2000).

In patients in whom noninvasive cross-sectional images fail to demonstrate crucial anatomy prior to resection or transplantation, angiography may be required. Sometimes a "spoke-wheel" arrangement of the arteries is present (Gazelle et al. 1998; Kirks and Griscom 1998).

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