Objective:The aim of this study was to study the clinicopathological and immunohistochemical features of pilomyxoid astrocytoma(PMA).Methods:The clinical and pathologic features in six cases of PMA were analyzed.Immunohistochemical staining for glial fibrillary acidic protein(GFAP),synaptophysin(Syn),Chromogranin A(CgA),cytokeratin(AE1/AE3),epithelial membrane antigen(EMA)and Ki67 was performed on paraffin-embedded sections.Results:Among the six cases,five occurred in female patients,one was male,the age at diagnosis ranged from 2 to 15 years.Four cases were located in the hypothalamic area and optic pathway,one case in the third ventricle,and one case in left parietal lobe.On imaging,PMAs often appears as well-circumscribed mass.Microscopically,the tumor was composed of monomorphous bipolar(piloid)cells setting in a prominent myxoid background with an angiocentric radiating growth pattern in some areas.PMA lacked biphasic pattern,Rosenthal fibers and eosinophilic granular bodies which were usually typical in a classic pilocytic astrocytoma(PA).Immunohistochemcal study showed that the tumor cells were diffusely positive for GFAP.Syn positive staining was observed in one case.The Ki67 labeling index measured less than 5%.Conclusion:PMA is a distinct aggressive variant of pilocytic astrocytoma with special histological and immunohistochemical features.It is typically a rare tumor of early childhood.Immunohistochemical staining for GFAP and Syn is helpful in differential diagnosis.
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