Dynamic Tumor Volume Changes after Debulking Surgery of Optic Hypothalamus Pilocytic Astrocytoma.

Debulking surgery is a treatment option for optic hypothalamic pilocytic astrocytoma. This study aimed to clarify the changes in magnetic resonance imaging following debulking surgery. We retrospectively reviewed the clinical and magnetic resonance imaging data of patients with optic hypothalamic pilocytic astrocytoma who underwent debulking surgery at Tohoku University Neurosurgery between January 2008 and August 2024. Tumor volume was measured using two-dimensional contrast-enhanced T1-weighted images before surgery, immediately postoperatively, up to 6 months, and beyond 6 months after surgery. These volumes were designated as V1, V2, V3, and V4 (mL), respectively. Time intervals from the day of surgery to the days when V2, V3, and V4 were assessed were defined as T2, T3, and T4 (days). An increase in tumor volume of 140% or greater compared with V2 was classified as enlargement according to the Response Assessment in Neuro-Oncology criteria 2.0. Nineteen debulking surgeries were performed on 10 patients. The median extent of resection was 55.6%. In nine of 14 surgeries without immediate adjuvant therapy, the ratio V3/V2 exceeded 140%. Despite this enlargement, no neurological deficits developed in these patients between T2 and T3. 5 patients were monitored without additional treatment, and 3 exhibited spontaneous tumor volume reductions by T4. In conclusion, early tumor enlargement commonly occurs within 6 months following debulking surgery for optic hypothalamic pilocytic astrocytoma; however, this enlargement can be transient in some cases. These findings suggest that a watchful waiting approach is a viable option for asymptomatic early enlargement after debulking surgery for OHPA.