Ovary : Leiomyoma
The muscle cells have elongated blunt-ended or cigar-shaped nuclei lacking cytologic atypia. Mitotic activity is not increased, except in mitotically-active leiomyomas which may have up to 15 mitoses/10 HPF (no atypical mitoses). Some leiomyomas have extensive hyalinization or epithelioid cells and may be misdiagnosed as sex cord-stromal tumors. The criteria for separating leiomyomas from leiomyosarcomas are similar to those used in the uterus. The presence of necrosis, severe cytologic atypia, and infiltrative margins favor leiomyosarcoma. The differential diagnosis includes fibroma (which is much more common than leiomyoma in the ovaries) and metastatic GIST. Ovarian leiomyomas can show infarction, hyalinization, cyst formation, and cellular and mitotically active areas similar to those seen in the uterine leiomyomas.