Table 2. Staging and risk stratification of medulloblastomas.

Modified Chang Staging
T stage		M stage
T1	Tumor <3 cm in diameter	M0	No evidence of gross subarachnoid or hematogenous metastasis
T2	Tumor ≥3 cm in diameter	M1	Microscopic tumor cells found in CSF
T3a	Tumor >3 cm and with extension into aqueduct of Sylvius or foramen of Luschka	M2	Gross nodular seeding intracranially beyond the primary site (in cerebellar/cerebral subarachnoid space or in third or lateral ventricle)
T3b	Tumor >3 cm and with unequivocal extension into brainstem	M3	Gross nodular seeding in spinal subarachnoid space
T4	Tumor >3 cm with extension past aqueduct of Sylvius or down past foramen magnum	M4	Metastasis outside cerebrospinal axis
Risk Stratification
Standard (Average) Risk (66%)		High Risk (34%)
>3 years old		<3 years old
<1.5 cm 2 residual disease after resection		Subtotal resection, >1.5 cm 2 residual tumor
M0 by craniospinal MRI and CSF		M+, leptomeningeal seeding, and location outside of the posterior fossa

CSF, cerebrospinal fluid; MRI, magnetic resonance imaging.