Table 1.

Refined SIOP EPII definitions of residual tumors (specific criteria that apply only for early postoperative MRI).

R0	No residual tumor on postoperative MRI in accordance with the neurosurgical report.
R1	No residual tumor on MRI but description of a small residual tumor by the neurosurgeon or if the neurosurgical result is unknown.
R2	Small residual tumor on MRI with the maximum diameter below 5 mm in any direction.
R3	Residual tumor that can be measured in 3 planes.
R4	Size of the residual tumor not differing from the preoperative status (e.g., after biopsy).
RX	If imaging is inadequate or the surgical cavity is very confusing, the term “unclear” should be possible. Every effort should be attempted to clarify the conclusion. Sometimes the presence of blood can be ruled out and distinguished from tumor if the MRI is repeated after some days. Repetition of MRI also may help to distinguish operative changes from residual tumor on T2-weighted-Fluid-Attenuated Inversion Recovery (T2/FLAIR).