Aggressive papillary tumor of the temporal bone - New immunohistochemical evidence for endolymphatic sac origin

Three cases of aggressive papillary tumor of the temporal bone are presented. The tumors showed histologic and immunohistochemical resemblance to non-tumorous endolymphatic sac. They contained abundant glycogen, and immunohistochemistry showed consistent positive staining for vimentin and glial fibrillary acidic protein. A similar staining pattern was found in three normal endolymphatic sac samples, contrary to previous reports in which staining for glial fibrillary acidic protein has been negative. In contrast, normal and inflamed middle ear mucosa and normal ceruminous glands were consistently negative for vimentin and glial fibrillary acidic protein. Our histological and immunohistochemical studies suggest that the three tumors reported here originated from endolymphatic sac, and radiological findings in one case also supported endolymphatic sac origin. However, it is by no means certain that all reported cases of papillary tumor of the temporal bone are endolymphatic sac tumors, since there is significant variation in the immunohistochemical staining pattern in previously reported cases.