Immunophenotype of myxopapillary ependymomas.

Myxopapillary ependymoma (MPE) is a slow-growing tumor occurring almost exclusively in the region of conus medullaris, cauda equina, and filum terminale. On microscopic examination, some of these tumors show solid sheets of cells with an epithelioid morphology mimicking a metastatic carcinoma. Several immunohistochemical studies addressed this issue with discordant results. We report the immunohistochemical findings of 9 additional cases of MPE. From 2004 to 2011, a total of 9 cases of MPE were recorded in our surgical pathology files. The histologic material and clinical data were reviewed for each case. There were 6 female and 3 male patients. The ages ranged from 15 to 58 years (mean, 31 y). Eight cases were intradural, lumbosacral (L1-S1), and 1 case was located in the sacrum. All tumors expressed CD99 and GFAP (100%). Eight tumors were positive for CD56 (89%). All tumors (100%) expressed focally CKAE1/AE3. One tumor (11%) was focally positive for CK8/18 and CK7. D2-40 was focally positive in 1 case (11%). PLAP and AFP were both negative in all cases. Synaptophysin was focally positive in 1 case. NSE was positive in all cases. All tumors were negative for CK5/6, CK20, E-cadherin, and TTF-1. Our study shows that the vast majority of MPE are positive for CD99, CD56, and GFAP. In selective cases, especially when the material obtained for pathologic evaluation is scanty and the tumor displays epithelioid appearance, the diagnosis may be challenging owing to cytokeratin positivity suggesting metastatic carcinoma. However, the clinical and radiologic features in addition to the positivity for GFAP should prompt pathologists to consider MPE in the differential diagnosis of such cases. Interestingly, we found that MPE are positive for NSE, which suggests a neuroglial differentiation.