Malignant choroid plexus papilloma of the IV ventricle.

We report a case of malignant choroid plexus papilloma (MCPP) of the IV ventricle in a child with prominent extraventricular expansive growth, mostly into the cerebellopontine angle. Interestingly enough, the tumor was entirely covered by thin, smooth, membranous, fibrous tissue, probably derived from the pia mater. In addition, hydrocephalus was not observed. The reason for the lack of hydrocephalus remains speculative, but it is possible that the presence of pure, nonexpansive, fibrous covering on the tumor might have suppressed the tumor growth to some extent, resulting in progressively increased intratumoral pressure. This, in turn, caused the suppression of excessive cerebrospinal fluid production by the tumor cells. From the diagnostic standpoint, immunohistochemical studies, using antiepithelial membrane antigen (EMA) and antitissue polypeptide antigen (TPA), were demonstrated to be useful for diagnosing the tumor.