Primary Peritoneal Ependymoma: A Case Report and Literature Review

Abstract Extra-axial ependymoma is a rare neoplasm. Reported anatomic sites include the ovary, para-ovarian tissues, pelvis, paracervical soft tissue, lung, omentum, small bowel, and posterior mediastinum. Primary peritoneal ependymomas are extremely rare. We report such an example in a 58-year-old woman who presented with abdominal pain, bloating, and history of a 70-lb weight loss over the prior year. Computed tomography scan showed a 20-cm pelvic mass extending into the abdomen and a 3.5-cm peritoneal-based right hepatic lobe/diaphragm mass. Histologic examination of the pelvic mass revealed an ovarian mucinous cystadenoma. The peritoneal mass showed a highly cellular solid neoplasm containing perivascular pseudorosettes and true ependymal rosettes. Tumor cell nuclei were rounded, oval, and elongated with coarse, granular chromatin and occasional small nucleoli. Mitoses were rare. Immunophenotype showed positive staining with bcl-2 and GFAP and scattered staining with keratins MNF116, CAM5.2, and cytokeratin AE1/AE3, along with chromogranin and EMA, but negative staining with inhibin, HMB45, SOX10, TLE-1, CD10, synaptophysin, Olig2, CD34, CD117, STAT-6, smooth muscle actin, and S-100. Conventional cytogenetic analysis showed normal chromosomes. Foundation One molecular profiling showed no actionable mutations. Ependymoma is an entity that rarely exists outside the central neuraxis having no connection with its central nervous system counterpart. Pathologic diagnosis is based primarily on presence of unequivocal ependymal differentiation.