Pigmented tumors of choroid plexus (CP) origin have only been reported a few times (1,2,3,4,5). The first reported case (1) was a CP carcinoma in the right lateral ventricle of a 33 male with metastases in the CNS and other organs. Electron microscopy demonstrated melanosomes in the obviously malignant cells. In 1979, a second case was reported of CP carcinoma in the left lateral ventricle of a 3 1/2 year old male. The pigmented material stained positive by Fontana-Masson but there were no melanosomes by electron microscopy. The authors concluded that the pigment was neuromelanin derived from melanization of lipofuscin.
In 1987, the first pigmented CP papilloma was reported in the Japanese literature (3). This tumor occurred in a 45 year old man and arose in the left lateral ventricle. It was heavily calcified by CT scans and had the histology of a typical benign papilloma. The pigment was Fontana-Masson positive but electron microscopy failed to demonstrate melanosomes or pre-melanosomes and the authors concluded that the pigment was neuromelanin. In 1990, another case was reported in a 15 year old male(4) who had a 10 year history of seizures. The tumor was described grossly as being "orangish-brown". Microscopically both dark brown, Fontana-Masson positve pignment and more abundant golden-brown, Fontana-Masson negative pigment was reported. Electron microscopy showed lipid associated granular material consistent with lipofuscin and neuromelanin, but there were no melanosomes. In 1995, a 4th ventricle tumor was reported in a 64 year old woman. The gross tumor was dark brown and nodular. Microscopically it was entirely papillary with benign epithelial cells containing abundant pigment. The pigment was Fontana-Masson positive and there were no melanosomes by electron microscopy. This was the first case in which imunohistochemistry was reported. They found the tumor to be positive for S-100 and focally positive for GFAP. It was negative with stains for vimentin, EMA and HMB-45.
In this case, the pigmented, nodular appearance of the tumor did not suggest a choroid plexus papilloma by gross examination. Although the neurosugeon suggested progonoma as a possible diagnosis, the histology of that tumor is of primitive neuroblast-like cells in clusters with scattered pigment and often abundant mitoses. These tumors typically occur in the jaw, but rarely have been reported in the CNS. While the microscopic and staining characteristics unequivocally establish this tumor as being derived from choroid, it does exhibit an unusual "inverted" architecture. While inverted papillomas of epithelial structures in other areas have long been described, such a pattern is distinctly unusual in a choroid plexus tumor. The immunostaining by CAM 5.2 and not by the cytokeratin cocktail AE1/AE3 indicates that choroid expresses only a few cytokeratins. We also stained normal choroid and a typical choroid plexus papilloma with AE1/AE3 and there was no staining with appropriate controls. Because cytokeratin staining can help distinguish a papillary ependymoma from a choroid plexus papilloma, this limited expression of cytokeratin by CP papillomas should be kept in mind.
In addition, this case is the first to demonstrate melanosomes in a melanotic CP papilloma. Previously these had only been found in cases of CP carcinoma (1). Also of interest is the identification of numerous HMB-45 positive cells. HMB-45 has been considered to be a "melanoma-specific" antibody, however, occasional reports of other tumors with positive staining have been published. Melanotic CP papilloma should now be added to that list.
While the choroid plexus origin of this tumor and the benign histology along with the complete resection would suggest a good prognosis, experience with these pigmented tumors of the choroid plexus is extremely limited and the prognosis should be guarded in this case.
Contributed by Ronald Hamilton, M.D.