Does an atypical choroid plexus papilloma exist?

The current WHO classification of tumours of the central nervous system lis ts two types of primary choroid plexus neoplasms: the choroid plexus papill oma (grade I WHO) and the choroid plexus carcinoma (grade III WHO). Sometim es individual cases, however, cannot be unequivocally classified into one o f these categories, but rather represent tumours of intermediate dignity. T his difficulty in grading of primary choroid plexus neoplasms is exemplifie d in a case report. Clinical findings: Nine-year old boy with a tumour in t he left lateral ventricle, local recurrence about one year following first surgery. Results: Histology of the first biopsy revealed in most parts a ra ther well-differentiated choroid plexus papilloma, but focally a marked cel lular pleomorphism and some mitoses were seen (MIB-1-proliferation index <1 0%). Classification as a choroid plexus papilloma (grade I WHO), but due to the increased proliferation index a close clinical follow-up was recommend ed. The recurrent tumour showed more obviously anaplastic histological feat ures with an increase in mitotic activity (MIB-1-proliferation index >10%) and focal necroses leading to classification as an anaplastic choroid plexu s tumour (grade III WHO). There were no significant differences in the morp hological appearance of the two biopsies using antibodies against prealbumi n/transthyretin, S-100 Protein, KL-1-cytokeratin. Conclusions: This case po ints to the problem of an only two-tired grading system of primary choroid plexus neoplasms, which sometimes may lead to discrepancies between the gra ding of the tumour and its actual biological behaviour. Therefore, consider ing relevant publications, we propose by analogy with the current three-tir ed WHO grading system of meningiomas the introduction of an "atypical choro id plexus papilloma" (corresponding to WHO grade II) with an increased tend ency for recurrence and for potentially anaplastic progression.