Pilocytic Astrocytoma Follow-Up Imaging: Recommendations Following Surgical Resection

Introduction: Pilocytic astrocytomas (PA) are the most common brain tumor in children, accounting for more than half of all primary childhood tumors of the CNS. However, there is no consensus on the frequency or duration of follow-up MRIs for patients with PAs after surgery. The authors aimed to establish a recommended framework for screening imaging following gross total resection (GTR) and subtotal resection (STR) of PAs.

Methods: Retrospective data analysis was performed for patients receiving GTR or STR for PA at our institution between 2006 and 2023. Demographics, clinical characteristics, MRI frequency during follow up period, treatment, and surgical history were collected. Recurrence and progression were defined by the year in which a radiologist noted this in a patient’s chart.

Results: Sixty-seven patients were included who received GTR (n=44; 40.9% female; mean age 9.5±5.23 years or STR (n=23; 35% female; mean age 6.64±5.1 years). Hydrocephalus was the most common presenting symptom (GTR – 65.9% and STR – 56%). For patients receiving GTR, the recurrence rates increased over the five-year follow up period (Y1 – 2.2%, Y2 – 2.2%, Y3 – 0%, Y4 – 2.2%, and Y5 – 6.8%). Annual imaging frequency decreased over the five-year period with many patients receiving only one MRI per year in years 3, 4, and 5. For patients with a STR, progression rates had a variable pattern over the five-year follow up period (Y1 – 17.3%, Y2 – 4.3%, Y3 – 0%, Y4 – 4.3%, and Y5 – 22%). Annual imaging frequency remained relatively consistent (3-month intervals) over the follow up period.

Conclusion : MRI frequency for PA should be based on trends in recurrence or progression. Our data suggests less frequent imaging is needed in the first three years for patients with a GTR, while more frequent imaging is needed for patients with a STR due to progression, especially within the first year.