Hepatobiliary Rhabdomyosarcoma RMS

Although RMS is the most common neoplasm of the biliary tree in children, it is a rare disease, accounting for approximately 1 % of all RMS in pedi-atric patients. RMS usually occurs in children of about three years of age and is rarely seen after the first decade of life. There may be a slight predominance among males [84].

Although the early histological classification of RMS was different in the United States [37] and Europe [12], a universal classification now exists [66]. Hepatobiliary RMS in childhood can be of the embryonal or botryoid types [84]. It may arise in the liver or intrahepatic bile ducts [54] in intra-hepatic cysts [85], the gallbladder [60], the cystic duct [49], the extrahepatic bile duct [49], the ampulla [14], or in choledochal cysts [73].

Microscopically, RMS contains spindle cell tumors in a myxoid stroma. A few cells have eosinophilic cytoplasmic tails resembling rhab-domyoblasts with or without cross striations [38]. Macroscopically, RMS tends to be well-demarcated from the surrounding tissue with a "pushing" margin. The mean diameter at diagnosis is usually about 8 cm [38,84].

The most common clinical features are jaundice and abdominal distension. Pain, nausea, vomiting and fever are less frequent. AFP values are normal [84,85].

US typically reveals biliary dilatation and an in-traductal mass [28, 32]. Although the portal vein may be displaced by a large tumor, portal vein thrombosis has not been described. Larger masses may have fluid, cystic areas within them, possibly reflecting tumor necrosis [63]. When the tumor arises in the liver, there may be no distinguishing US features (Fig. 15). Color Doppler US may reveal numerous abnormal tumor arteries with low resistive index [79]. The same is seen on catheter angiography, indicating a malignant neoplasm (Fig. 16).

CT also reveals an intraductal mass with or without biliary dilatation (Fig. 17). Hypodense and heterogeneous attenuation patterns have been described [32] and areas of low attenuation within the tumor may be present [14, 54, 63, 73]. Enhancement patterns after the administration of contrast material have been described as strong heterogeneous, incomplete globular, mild and none [79], indicating that enhancement may be variable.

RMS is generally hypointense on unenhanced T1-weighted MR images and moderately or markedly hyperintense on T2-weighted images.

Fig.15. Hepatobiliary rhabdomyosarcoma. US reveals a large mass with internal cystic areas (arrows) that reflect tumor necrosis and dilated bile ducts

Fig. 16. Hepatobiliary rhabdomyosarcoma. Catheter angiography demonstrates numerous abnormal tumor vessels, indicative of a malignant liver tumor, within a hepatobiliary rhabdomyosarcoma

Fig.15. Hepatobiliary rhabdomyosarcoma. US reveals a large mass with internal cystic areas (arrows) that reflect tumor necrosis and dilated bile ducts

Fig. 16. Hepatobiliary rhabdomyosarcoma. Catheter angiography demonstrates numerous abnormal tumor vessels, indicative of a malignant liver tumor, within a hepatobiliary rhabdomyosarcoma

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Fig. 17a-c. Hepatobiliary rhabdomyosarcoma. The unenhanced CT image (a) shows a hypodense tumor with heterogeneous attenuation pattern. Low attenuation areas are apparent within the tumor. Following the injection of contrast medium, the tumor shows heterogeneous enhancement in the arterial phase (b) with depiction of multiple irregular vessels within the tumor. In the portal-venous phase (c) most of the tumor shows wash-out of contrast medium resulting in a more heterogeneous appearance. Multiple cystic areas within the tumor (arrows) and displacement of the portal vein by the tumor (arrowheads) can be noted

Fig. 18a-e. Hepatobiliary rhabdomyosarcoma. Same case as shown in Fig. 17. The unenhanced T2-weighted HASTE images in axial (a) and coronal (b) orientation show a large hyperintense tumor with heterogeneous SI and multiple cystic areas. The corresponding unenhanced Tl-weighted image (c) reveals a tumor with low SI in which areas of bright signal (arrows) indicate intratumoral hemorrhage. Following the injection of contrast agent (d, e), the solid portions of the tumor show homogeneous enhancement whereas the cystic areas remain hypointense. Note again that the tumor has displaced the portal vein and is sharply demarcated from the surrounding liver tissue

Fig. 18a-e. Hepatobiliary rhabdomyosarcoma. Same case as shown in Fig. 17. The unenhanced T2-weighted HASTE images in axial (a) and coronal (b) orientation show a large hyperintense tumor with heterogeneous SI and multiple cystic areas. The corresponding unenhanced Tl-weighted image (c) reveals a tumor with low SI in which areas of bright signal (arrows) indicate intratumoral hemorrhage. Following the injection of contrast agent (d, e), the solid portions of the tumor show homogeneous enhancement whereas the cystic areas remain hypointense. Note again that the tumor has displaced the portal vein and is sharply demarcated from the surrounding liver tissue

Following the administration of a Gd contrast agent, intense but inhomogeneous contrast enhancement is usually seen (Fig. 18) [79].

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