Criteria
World Health Organization (WHO) classification of tumors of the central nervous system (2021)[4]
Diagnosis is based on the pathologist's review of the gross specimen, the microscopic findings, and immunohistochemical staining.[4] In rare cases in which histopathology is not clearly diagnostic, tumor DNA/RNA sequencing and DNA methylation analysis can be used to confirm diagnosis and further classify the tumor molecular subgroup and clinical risk.[36]
Modified Chang classification[37][38]
No longer used alone but, particularly the M stage, can help inform treatment decisions and prognosis when considered alongside other factors including the age of patient, completeness of resection, histologic subtype, and genetic markers.[39]
Primary tumor
TX - Primary tumor cannot be assessed
T0 - No evidence of primary tumor
T1 - <3 cm in diameter
T2 - ≥3 cm with no evidence of extension
T3a - >3 cm with extension into aqueduct of Sylvius or foramen of Luschka
T3b - >3 cm with spread into brain stem
T4 - >3 cm with extension past aqueduct of Sylvius or foramen magnum.
Distant metastases
M0 - No dissemination
M1 - Microscopic tumor cells present in the cerebrospinal fluid (CSF)
M2 - Gross nodular seeding intracranially beyond the primary tumor site (cerebellum, cerebral subarachnoid space, or in the third or fourth ventricles)
M3 - Gross nodular seeding in the spinal subarachnoid space
M4 - Metastasis outside the cerebrospinal axis.
Clinical classification of medulloblastoma
Average-risk tumor
ages ≥3 years without evidence of metastatic spread and having ≤1.5 cm² (maximum cross-sectional area) of residual disease after surgery and no histologic or molecular high-risk factors (below).[3][40]
High-risk tumor
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