眼窩横紋筋肉腫の微細構造

Ultrastructure of Rhabdomyosarcoma of the Orbit

緒言

　横紋筋肉腫は小児の眼窩内悪性腫瘍のうち頻度の高いものの1つであり，眼窩は好発部位の1つである。しかし光学顕微鏡では横紋の確認が比較的困難なため，現在までわが国での報告例は，著者らの集計では22例にすぎない。

　近年，電子顕微鏡を用い，比較的容易に細胞内筋線維が証明されるようになつたが，その微細構造は眼窩部^{1）〜3）5）31）}，耳^4），骨格筋^5）6）（顔面，四肢），前立腺^7）に原発した横紋筋肉腫で報告されている。

An ultrastructural study of three cases of embryonal rhabdomyosarcoma arising from orbi-tal region of a 8-year-old girl, 2-year-old and 5-year-old boys is reported. Cross striations in neoplastic cells were found in a case of 8-year-old girl under the light microscope and not in the other two cases.

The electron microscopy, however, revealed not only well arranged myofilaments in the first case but also undifferentiated poorly form-ed fibers in the latter two cases. Myofibrils in the cytoplasm were of two types : one typewas thick and the other was thin.