Ultrastructure of botryoid sarcoma of the common bile duct

The ultrastructure of poorly differentiated rhabdomyosarcomas: a case report and literature review

The ultrastructure of a case of rhabdomyosarcoma is reported, and the world literature on the ultrastructure of rhabdomyosarcomas is reviewed. The reported case was first observed as an undifferentiated malignancy originating in the maxillary antrum of a 46-year-old white woman and later showed differentiated cells in metastatic sites. A specific feature of the sarcomere within a representative malignant cell is necessary and sufficient for diagnosis of rhabdomyosarcoma by ultrastructure. Examples of specific features include thick and thin filaments in a hexagonal array, an unambiguous Z line, or A bands with H and M bands. The presence of thick and thin filaments without additional features of the sarcomere indicate a myogenous origin, either leiomyosarcoma or rhabdomyosarcoma. Other ultrastructural features observed in rhabdomyosarcomas, for which the diagnosis is confirmed by the presence of diagnostic ultrastructural features or by the presence of cross-striations observed by light microscopy, include large irregularly shaped nuclei with projections and invaginations, free ribosomes closely associated with filaments, rough endoplasmic reticulum that is often dilated, glycogen, and external lamina, prominent nucleoli, and pleomorphic mitochondria. When this spectrum of features is present, the possibility of rhabdomyosarcoma cannot be excluded, and a diligent search for the diagnostic components of the sarcomere should be made. Small intercellular junctions, pinocytotic vesicles, and paranuclear cilia occurred in the poorly differentiated metastasis of this case; the presence of these nonspecific features permits neither diagnosis nor exclusion of rhabdomyosarcoma.

Morphological changes of myofibril in the carcinogenetic course of 20-methylcholanthrene-induced rhabdomyosarcoma

In this study 20-methylcholanthrene (MC) was embedded in skeletal muscle tissue of mice. The resulting morphological changes were observed by light and electron microscope until the occurrence of rhabdomyosarcoma. The injected region of the muscle tissue in which MC was embedded went through three stages: destruction and degeneration, repair and appearance of atypical cells. The morphologic figures of the myofibrils seen in the skeletal muscle cell during destruction and degeneration were similar to nonspecific. The muscle tissue then regenerated in the same manner as seen during experimentally induced muscle tissue regeneration in both humans and animals. Abnormal mitotic figures were found 60 to 70 days after the injection of MC. Immature muscle cells, with tuft-formed myofibrils present, underwent abnormal mitosis in which one of the nuclei divided. The rhabdomyosarcoma cells produced by this abnormal mitosis began to appear in the lesion 70 days after the initial embedding of MC. The rhabdomyosarcoma cells in the induced tumor formed undifferentiated myofibrils in various degrees of maturation, and were therefore considered to play a part in the abnormal myofibrillar formation.