Villous hypertrophy versus choroid plexus papilloma: a case report demonstrating a diagnostic role for the proliferation index. 
Diffuse bilateral enlargement of the choroid plexus has long been appreciated as a cause of shunt-resistant hydrocephalus in infants, most often secondary to cerebrospinal fluid overproduction.  Despite the fact that such lesions have interchangeably been termed 'villous hypertrophy' (VH) or 'bilateral choroid plexus papilloma' (CPP), little attention has been paid to the pathological distinctions that characterize these two entities.  We present a case of presumed VH in a 2-week-old female presenting with cerebrospinal fluid production-dependent hydrocephalus that ultimately required bilateral surgical ablation of the choroid plexus.  Although the preoperative radiological diagnosis was consistent with VH, postoperative histological analysis suggested bilateral CPP.  The neoplastic nature of the lesion was confirmed by specific staining for the proliferation index, showing an MIB-1 labeling index of 4%, characteristic of papilloma.  Routine imaging and histological grading of choroid plexus hypertrophy and papilloma have not provided a reliable means of predicting malignant behavior or recurrence after surgical resection.  Moreover, none of the previously reported cases of VH in the literature have analyzed pathological specimens for cellular proliferative potential.  Therefore, we review the literature on VH and bilateral CPP and discuss the diagnostic and possible prognostic implications of distinguishing these variants by utilizing the MIB-1 marker for the proliferation index.