The Role of Glial Fibrillary Acidic Protein (GFAP) and Epithelial Membrane Antigen (EMA) in the Differentiation and Diagnosis of Glial Tumors

Background: CNS tumors diagnosis represents a challenge in histopathological examination. EMA and GFAP are widely used markers in neurosurgical pathology that help in the diagnosis of many commonly occurring tumors and differentiating them from other mimickers.Aim of study: To assess the value of EMA and GFAP in the diagnosis of ependymal tumors compared with other glial tumors. Evaluate the pattern of expression of these markers. The value of glial fibrillary acidic protein positivity in the diagnosis of ependymoma and diffuse fibrillary astrocytoma.Materials and method: The present study is a retrospective study over a period of one year, the paraffin blocks were collected from the archive of the department of pathology, Ghazi Al –Hariri specialized surgical hospital, over the period of 4 years, from March 2015 to October 2019, they included 15 cases of ependymoma and 15 cases of diffuse fibrillary astrocytoma. Total number was 30 cases. The markers used were EMA, and GFAP. The manual method of staining was used in this study.Result: Both markers showed positivity in studied cases, the finding of 5 EMA dots/ high-power field was associated with a sensitivity of 86% and a specificity of 80%. The presence of ring-like EMA positive structures was less sensitive (33%), but highly specific (100%). GFAP was useful in highlighting the growth pattern of these tumors, and in ependymoma it was mostly expressed in cells and fibrillary processes around vessels (pseudorosettes) and in true rosettes.Conclusion: Distinct punctate and ring like EMA staining might serve as sensitive and specific markers of ependymal differentiation in glial tumors and, thus, may aid the diagnosis of ependymoma. As for GFAP marker, although it was expressed in both ependymoma and glial tumors, it can provide significant value in highlighting the growth pattern of these tumors, and in excluding other mimickers.