Proliferative activity and histopathological features in diffuse grade II astrocytomas

Due to the heterogeneous histopathology of diffuse astrocytomas we wanted to investigate the frequency of various histological features in grade II tumours. Herein we present the results of a microscopical examination and revision of 109 consecutively operated grade II tumours. The most frequent subtype was fibrillary astrocytoma (87%), whereas the gemistocytic and protoplasmic subtypes constituted 12% and 1% respectively. Cell density was subjectively classified and ranged from low to high; most cases were judged as low to moderate (approx. 90%). Cellular/nuclear atypia was assessed as mild, moderate and severe, and was in the majority of cases mild to moderate (96%). Mitoses were observed in about 25% of the cases with a median of 0 (range 0-3). Apoptotic figures, microcystic changes, Rosenthal fibres, microcalcification and eosinophilic bodies were identified in approx. 45%, 38%, 7%, 5% and 2% of the cases respectively. In about 60% of the cases so called secondary changes of Scherer were seen. Significant correlations between features related to malignancy, such as mitotic activity, apoptoses and high cell density, were established. Further, Ki-67/MIB-1 proliferation indices corresponded significantly with mitoses, apoptoses, atypia and high cell density. Accordingly, the variegated histopathological appearance of diffuse astrocytomas makes the diagnosis of these tumours challenging. Accordingly, it is essential to know and be aware of this morphological diversity in the daily routine. The use of Ki-67/MIB-1 immunostaining may improve the diagnostic accuracy.