Staging involves:
1. MR of the craniospinal axis to exclude subarachnoid metastasis:
- Preferably prior to surgery or at least 21 days after surgery
2. Post-op CT or MR of the head to determine if there is any gross residual disease:
- Preferably prior to surgery or less than 24 to 48 hours after surgery
3. Lumbar puncture for CSF cytology:
- A minimum of 10 days after surgery
Chang Staging System:
The Chang system was published in 1969 and was the most widespread classification system for the staging of medulloblastomas. However, it is really no longer used regularly in clinical practice.
This staging system was developed in the pre-CT era and is based on:
- Size and invasiveness of the primary tumor at surgery, denoted as the “T stage” or tumor stage.
- Evidence of spread outside the posterior fossa, marked as the“M stage” or metastatic stage.
Chang staging system for medulloblastoma:
|
T1 |
Tumor <3 cm in diameter |
T2 |
Tumor >3 cm in diameter |
T3a |
Tumor >3 cm in diameter with extension |
T3b |
Tumor >3 cm in diameter with unequivocal extension into the brainstem |
T4 |
Tumor >3 cm in diameter with extension up past the aqueduct of Sylvius and/or down past the foramen magnum (ie. Beyond the posterior fossa) |
M0 |
No evidence of subarachnoid or hematogenous metastasis |
M1 |
Tumor cells found in cerebrospinal fluid |
M2 |
Intracranial tumor beyond primary site |
M3 |
Gross nodular seeding in spinal subarachnoid space |
M4 |
Metastasis outside the cerebrospinal axis (especially to bone marrow, bone) |
(Source: Pediatric Radiation Oncology; Halperin, Constine, Tarbell, Kun)
According to the above system, an increase in tumor size and invasion of the brainstem define aggressive behavior of the tumor. These are classified as T1 to T4.
Several pediatric studies have shown that the M stage, the amount of residual disease after surgery and the age of the child are more predictive of outcome.
Extraneural disease is very rare, found in less than 2% of cases, and is most often in the bone marrow in the setting of widespread intracranial and spinal disease.
M stage:
- Based on subarachnoid metastases, coding for the progressive appearance of tumor in cerebrospinal fluid (M1), in the cranium (M2) or in the spine (M3).
- The M stage continues to be a highly significant prognostic factor in determining the intensity of therapy that is appropriate as well as predicting the outcome for the patient.
Risk Category:
Current protocols for clinical trials and and patient management across North America groups patients into categories of “average risk” and “high risk”.
This grouping principle allows for the treatment to be more precisely tailored to the extent of disease.
Average risk children are those older than 3 years with no detectable metastatic disease after near total or total resection.
High-risk patients are those with overt metastatic disease based on CSF cytology or neuroimaging. All children under 3 years of age are now classified as high risk due to the predictions of outcome studies.
Risk Category |
Characteristics |
Average (also sometimes called good or standard risk) |
>3 years
Near or total resection (less than 1.5 cm2 of residual disease)
|
High (also sometimes called poor risk) |
<3 years
Gross residual disease (more than or equal to 1.5 cm2 of residual disease)
|
External Link:
Staging of CNS Embryonal Tumors at the National Cancer Institute
