RESUMEN
AIMS AND BACKGROUND: To report an extremely rare case of Ewing's sarcoma located in the rectovaginal septum. Ewing's sarcoma is a highly malignant neoplasm of bone, which usually occurs during childhood. Common extraosseous localizations of Ewing's sarcoma include the trunk, extremities, uterus, cervix and vagina. METHODS: A 45-year-old woman presented to us with a six-month history of pain in the lower abdomen during intercourse. Pelvic examination was performed and a palpable mass was found. The mass had a size of 9 x 6 cm, a soft tissue consistency, was partially movable and the patient felt the pain during palpation. Examination of the inguinal lymph nodes revealed no signs of inguinal adenopathy. The results of laboratory tests, rectoscopy, chest X-rays, barium enema and bone scan were normal. Computed tomography (CT) showed an inhomogeneous expansive mass in the rectovaginal septum measuring 8.7 x 6.1 cm, without any signs of rectum or bladder invasion. The vascular structures of the pelvis were normal. At laparotomy the process was judged inoperable and only biopsy of the tumor mass was carried out. Histology showed a neoplasm with small, round to oval cells with scarce cytoplasm. Immunohistology with the monoclonal antibody CD99 (MIC-2 gene product, Ewing's sarcoma marker, clone 12E7, DAKO A/S, Glostrup, Denmark) revealed an extraosseous Ewing's sarcoma. The patient was treated with chemotherapy followed by whole-pelvis external beam radiation and intracavitary brachytherapy. RESULTS: A residual mass measuring 3.5 x 2.5 cm was visible on a control CT scan 18 months after treatment; however, the patient was feeling well and refused surgery to remove the residual mass. CONCLUSIONS: To our knowledge this is the first reported case of extraosseous Ewing's sarcoma in the rectovaginal septum.