Atypical central neurocytoma.

The proliferative potential of central neurocytomas was determined in a biopsy series of 36 cases and compared with clinical outcome. The mean size of the growth fraction, as determined by MIB-1 labeling index (MIB-1 LI) at first biopsy, was 2.8 +/- 2.5 with a range of 0.1 to 8.6%. Neurocytomas with an MIB-1 LI > 2% comprised 39% of cases and showed a close correlation with the presence of vascular proliferation (p = 0.0006). The Kaplan-Meier analysis showed a highly significant difference in disease-free survival between the 2 groups (p = 0.0068). Over an observation time of 150 months, there was a 22% relapse among patients with an MIB-1 LI less than 2% and a 63% chance of relapse among those with an MIB-1 LI greater than 2%. We propose the term "atypical central neurocytoma" for the latter subset, corresponding to WHO grade II.