Differential expression of transthyretin in papillary tumors of the endolymphatic sac and choroid plexus.

Aggressive papillary tumors of the temporal bone, occurring sporadically or as part of von Hippel-Lindau disease, have been shown to originate within the endolymphatic sac or duct. Also implicated as a potential precursor from which some of these tumors may arise is ectopic choroid plexus epithelium. To aid in the differentiation between papillary tumors of endolymphatic sac and duct origin and those arising from choroid plexus, an immunohistochemical study using stains for transthyretin (TTR), cytokeratins, S-100 protein, epithelial membrane antigen (EMA), and glial fibrillary acidic protein (GFAP) was carried out on archival specimens of normal and neoplastic endolymphatic sac and duct and choroid plexus epithelium. Transthyretin, a marker for choroid plexus epithelium, was found to show differential expression between choroid plexus papillomas and aggressive papillary tumors of the endolymphatic sac or duct. Therefore the use of TTR in concert with other immunohistochemical stains appear to aid in the differentiation between intracranial and intratemporal papillary tumors arising from choroid plexus and endolymphatic sac or duct epithelium.