| Histologic criteria | gr1 | gr2 | gr3 | gr4 |
| Lobular architecture | ++ | + | − | − |
| Neuropil | ++ | + | +/− | − |
| Rosettes | +/− | +/− | +/− | − |
| Necrosis | − | − | + | ++ |
| Pleomorphism | − | + | ++ | +++ |