Tumors of the Striated Muscle Cell Lineage: Hepatobiliary Rhabdomyosarcoma and Rhabdomyoma

Abstract

Rhabdomyosarcomas (RMS) are a group of aggressive malignancies derived from a skeletal muscle cell lineage. These neoplasms occur in several distinct body regions in children and adults. One subset of RMA develops in the hepatobiliary tract, mainly in the pediatric age group, associated with a distinct clinical and radiological syndrome. Hepatobiliary RMS is defined as a mucosal-type RMS arising from the wall of intrahepatic or extrahepatic bile ducts. This neoplasm is the most common biliary tract tumor in children, but is overall rare, accounting for only 0.8 % of all RMS and 1.3 % of malignant liver tumors in childhood. The neoplasm can form polypoid masses that protrude into the bile ducts. Histologically, most hepatobiliary RMS are embryonal RMA, whereas alveolar RMS is a very rare hepatic malignancy. Histologically, embryonal RMA of the liver shows a loose neoplastic tissue with desmin-positive stellate cells and cells resembling rhabdomyoblasts. Frequently, a cellular layer is found underneath the biliary tract epithelium, the so-called cambium. RMS of the hepatobiliary tract can rarely also occur in adults.