The many faces of smooth muscle neoplasms in a gynecological sampling: an ultrastructural study

Smooth muscle neoplasms may have a variety of light microscopic and ultrastructural appearances. On one extreme, a spindle cell mass with a fascicular pattern, located in the myometrium, usually does not need electron microscopy or immunohistochemistry to confirm its smooth muscle nature. However, at the other end of a spectrum is an epithelioid neoplasm of the extrauterine pelvic tissues that could be composed of any of several cell types if routine light microscopy, alone, were used in studying it. In this report, some of these variants of smooth muscle neoplasms are exemplified, including myxomatous, fibroblast-like, nondescript, epithelioid, granular cell, and clear cell types. The main purpose has been to address, in particular, the ultrastructure of these unusual neoplasms, but, at the same time, not to ignore or downplay the contributory role of immunohistochemistry in making a final diagnosis, in some cases. Especially intriguing were the ultrastructural characteristics of leiomyomatous granular cell and clear cell neoplasms. A paucity or absence of filaments and dense bodies in samplings of these lesions makes the reliance on other ultrastructural features extremely useful.