Central neurocytoma: histologic atypia, proliferation potential, and clinical outcome

BACKGROUND: Although central neurocytomas are considered benign, recent reports suggest that some patients with histologic atypia and/or elevated proliferation potential may have a poor outcome. METHODS: A retrospective review identified 15 cases of central neurocytoma. Clinical follow-up was available for 14 patients. Each tumor was evaluated for the presence of atypical histologic features, including cellular pleomorphism, endothelial proliferation, and necrosis. The proliferation potential was assessed by MIB-1 immunohistochemistry. The correlation among histology, MIB-1 labeling index (MIB-1 LI), and clinical outcome was evaluated. RESULTS: Histologic atypia was identified in 3 tumors (20%). The MIB-1 LI ranged from 0.1% to 6.0%, and 5 cases (33%) had an MIB-1 LI >2%. The correlation between histologic atypia and MIB-1 LI was poor, with only 1 tumor having both atypia and MIB-1 LI >2%. Clinical follow-up ranged from 13 to 255 months postoperatively (mean, 68 months). Although most patients were alive and well at last follow-up, three developed symptomatic recurrence and one died as a result of increased tumor growth. The tumors from all 4 patients with a poor outcome had MIB-1 LI >2%, but only 1 had histologic atypia. CONCLUSIONS: The proliferation potential of central neurocytoma is a useful predictor of clinical outcome, whereas histologic atypia alone is not prognostically significant. It would be appropriate to recognize a subgroup of central neurocytomas with elevated proliferation potential as WHO Grade 2 lesions. The terms "atypical" and "anaplastic" are not appropriate to describe these lesions, as they imply a certain histologic appearance. The most accurate designation would be "proliferating neurocytoma."