Duplication of 9P and hyperplasia of the choroid plexus: a pathologic, radiologic, and molecular cytogenetics study.

Duplication of the short arm of chromosome 9 is a rare constitutional abnormality, and the presence of pathologically confirmed hyperplasia of the choroid plexus in one of two cases, and a choroid plexus papilloma in another, raises the possibility of a relationship between the 9p abnormality and abnormal growth of the choroid plexus. Molecular cytogenetic analysis using fluorescence in situ hybridization was used for detection of chromosome 9-derived material in various formalin-fixed choroid plexus abnormalities. Extra copies of chromosome 9-derived material was found in the hyperplastic choroid plexus and in a choroid plexus carcinoma. These findings suggest that there may be an association between duplication of chromosome 9 material and abnormal development of the choroid plexus.