MRI Surveillance Timing After Craniospinal Irradiation in Pediatric Patients
Follow-up brain MRI should be performed every 2 cycles during therapy (but no less frequently than every 3 months), with surveillance spine imaging done concurrently with brain imaging in patients who had initially positive radiographic findings or positive CSF cytology at baseline. 1
Brain MRI Surveillance Schedule
During Active Treatment:
- Perform brain MRI every 2 cycles of chemotherapy, with an absolute minimum frequency of every 3 months 1
- This surveillance begins after the baseline postoperative imaging and continues throughout the chemotherapy phase that follows craniospinal irradiation 1
Post-Treatment Surveillance:
- Continue regular brain MRI surveillance with decreased frequency after completion of therapy, though the guidelines acknowledge institutional variation in exact timing 1
- The evidence supports that most recurrences occur within the first 3-4 years after diagnosis, making this the critical surveillance window 1
Spine MRI Surveillance Schedule
High-Risk Patients (M+ disease or positive CSF cytology at baseline):
- Perform spine MRI concurrently with every brain MRI during and after treatment 1
- This approach is justified because up to 20% of medulloblastoma patients may develop isolated spinal metastasis, and most are asymptomatic 1
Average-Risk Patients (M0 disease, negative CSF):
- The guidelines acknowledge significant practice variation, with some centers performing spine surveillance less frequently than brain imaging 1
- European practice typically performs spine screening only at diagnosis, with follow-up reserved for patients who develop new spine symptoms or have metastasis detected by CSF 1
- However, given that 5-7% of patients may develop isolated spinal leptomeningeal metastasis (often asymptomatic), risk-stratified spinal surveillance MRI is recommended, particularly during the first 3-4 years after diagnosis 1
Critical Timing Considerations
Baseline Post-Radiation Imaging:
- The first surveillance MRI after completing craniospinal irradiation should align with the start of chemotherapy, which begins 6 weeks after radiation completion 2
- This timing allows assessment of response before initiating systemic therapy 2
Molecular Subtype Considerations:
- Sonic hedgehog subgroup patients have higher propensity for local recurrence, while Groups 3 and 4 have more frequent leptomeningeal recurrences 1
- Despite these differences, isolated spinal metastases occur in all subgroups and may recur relatively late, supporting continued surveillance across all molecular subtypes 1
Technical Imaging Requirements
Essential Sequences:
- Include diffusion-weighted sequences at every timepoint, as hypercellular tumors like medulloblastoma present with hyperintense signal that helps identify both primary site and metastatic deposits 1
- Obtain contrast-enhanced T2 FLAIR images after contrast administration, as these are highly sensitive for leptomeningeal disease 1
- Use postcontrast 3D T1-weighted fast spin echo sequences (SPACE/Cube/VISTA) to minimize vascular signal artifacts 1
Common Pitfalls to Avoid
Do not perform spine MRI immediately after surgery (within 72 hours) if extensive postoperative enhancing subdural effusions are present, as these can obscure metastases; instead, delay spine MRI for 2-3 weeks post-surgery to avoid false-positive findings from blood products 1, 2, 3, 4
Do not reduce surveillance frequency prematurely in the first 3-4 years after diagnosis, as this is when most recurrences occur, including asymptomatic isolated spinal metastases 1
Do not rely solely on symptoms to trigger spine imaging in high-risk patients, as studies show that only 7 of 19 patients (37%) with leptomeningeal recurrence were symptomatic 1
Do not skip concurrent spine imaging in patients with initially positive radiographic findings or positive CSF cytology, as these patients require comprehensive craniospinal surveillance 1