Cellular Leiomyomas and Highly Cellular Leiomyomas

• These tumors grossly may resemble typical leiomyomas but often have a fleshier, soft, yellow or brown sectioned surface, sometimes with hemorrhage and/or necrosis. They may be less well circumscribed than typical leiomyomas.
• Cellular leimyomas are defined as leiomyomas that are 'significantly' more cellular than the normal myometrium but which are otherwise typical.
• Highly cellular leimyomas (HCL) are characterized by a cellularity similar to that of an endometrial stromal tumor (EST), and may be misdiahnosed as an endometrial stromal nodule when well circumscribed.
• Features that facilitate the distinction of HCLs from an EST and include a fascicular growth pattern, spindle-shaped tumor cells, blood vessels with thick muscular walls, cleft-like spaces, and immunoreactivity for desmin and h-caldesmon. About 40% of HCLs are CD10 positive, but CD10- negativity favors HCL over an EST.
• Recently described markers that are expressed in smooth muscle tumors but not stromal tumors that may also aid this differantial are indicated elsewhere.
• The differantial of CLs also includes focal hypercellularity of the myometrium. This finding is more common in postmenopausal women and tends to involve superficial myometrium immediately subjacent to the endometrium. The absence of a mass, the sometimes band-like arrangement, and merging with normal myometrium facilitate the diagnosis.