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HIGHLY CELLULAR LEIOMYOMA
Comment:
The differential diagnosis is between an endometrial stromal tumor (endometrial stromal nodule, endometrial stromal sarcoma) and a highly cellular leiomyoma. Although the immunohistochemical stains can be helpful if CD10 negative, a high percentage of cellular leiomyoma mark with CD10, a stain traditionally assumed to mark stromal tumors. Conversely, endometrial stromal neoplasms with smooth muscle differentiation will mark with muscle markers.
The characteristic features of highly cellular leiomyoma are the cleft like spaces at the edge of the tumor, the thick-walled vessels within the tumor, and the "spindled" spindle cells as opposed to rounded spindled cells. They also lack the spiral arterioles characteristic of endometrial stromal neoplasms. The edge of a cellular leiomyoma is often irregular, sometimes raising concern not for an endometrial stromal nodule (which if misdiagnosed as, has no clinical implications) but for an endometrial stromal sarcoma (which does have prognostic and surgical implications). The irregular tongues of tumor in cellular leiomyoma are generally small, do not extend for more than a few millimeters beyond the tumor and "fade" into the surrounding myometrium; whereas these tongues are sharply circumscribed in endometrial stromal sarcoma.
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