LAUSR

A 51yearold woman with a prior history of papillary thyroid carcinoma presented with hemoperitoneum and hypovolemic shock secondary to a ruptured pelvic mass. Total abdominal hysterectomy with bilateral salpingooophorectomy was performed and 1.5 L of blood were drained. Gross examination showed a 12 cm ruptured cystic mass appearing to originate from the left fallopian tube. The cyst was hemorrhagic with numerous blood clots admixed with tanwhite nodules measuring up to 2.8 cm. The left mesosalpinx and mesovarium were grossly involved but surface involvement of ovaries, uterus, and the right fallopian tube was not identifiable. Histopathological analysis showed solid sheets of small cells with uniform nuclei and stippled chromatin. Cytoplasm was scant but often included glycogenic droplets (Figure 1). Mitotic activity was brisk with atypical mitotic figures. Large hemorrhagic lakes and pools were identified among tumor cells giving rise to a ‘pseudovascular pattern’, concerning for angiosarcoma. However, the tumor also exhibited HomerWright rosettes, which consisted of palisaded cells around pink neurofibrillary processes (Figure 2). Presence of tumor within the left ovarian parenchyma made it difficult to distinguish a primary tubal or ovarian origin. Furthermore, tumor implants were identified at the serosal surfaces of the uterine cervix, uterine corpus, both ovaries as well as the left mesosalpinx and left mesovarium. There was no associated teratoma or malignant mullerian neoplasia within the tubes or ovaries. Immunohistochemical staining showed diffuse positivity for membranous CD99 (Figure 3) and nuclear FLI1. OCT 3/4, and S100 were also positive. Synaptophysin, CD56, chromogranin A and B, Melan A, MART1, HMB45, ER, calretinin, inhibin, AFP, cytokeratin AE1/AE3, BerEP4, EMA, SALL4, PAX2, p53, WT1, CD34, and factor VIIIrelated antigen were negative. Rare isolated cells stained for PAX8, GFAP, and PR. The histopathological and immunohistochemical findings were consistent with tuboovarian extraosseous Ewing sarcoma, which has historically been designated as peripheral primitive neuroectodermal