A case of choroid plexus papilloma with stromal sclerosis and indistinct papillary structures.

We present a case of choroid plexus papilloma with unusual histopathological findings. A 41-year-old Japanese man presented with dizziness. Brain magnetic resonance imaging scan showed a distinct mass in the fourth ventricle. Histopathological examination showed proliferation of cuboidal cells forming irregular trabeculae, small nests, and pseudoglandular and indistinct papillary structures, accompanied by a variable degree of stromal sclerosis. The tissue sections also showed rare mitotic activity, no hypercellularity, cellular pleomorphism, or necrosis. The immunohistochemical findings were tumor cells positive for cytokeratin 7, vimentin, S-100 protein, and transthyretin but negative for cytokeratin 20, BerEP4 and carcinoembryonic antigen. These findings were consistent with choroid plexus papilloma. The combination of these immunohistochemical markers was helpful in establishing the diagnosis, although the morphological finding of stromal sclerosis is rare for choroid plexus papilloma.