Impact of Surgical Resection on Tumor Growth Dynamics in Pediatric Pilocytic Astrocytomas

INTRODUCTION Pilocytic astrocytoma (PA) is the most common pediatric brain tumor and generally exhibits slow growth and favorable outcomes. However, postoperative growth behavior of residual or recurrent tumors remains variable and not well quantified. This retrospective study aims to quantify the tumor growth velocity (TGV) of PAs in a pediatric population and estimate the influence of surgery on these values. We also aimed to determine the impact of absolute and relative measurements on these conclusions. METHODS Only pediatric patients with a histopathologically confirmed diagnosis of PA and with at least two consecutive MRI scans performed at an interval of at least 3 months were included in this study. Patients were excluded if the quality of their imaging data was poor or if additional treatments (e.g. chemotherapy or radiotherapy) were administered. Absence of residual tumor was an exclusion criterion, as visual tumor is necessary for the calculation of growth velocity. Thus, patients who underwent gross total resection (GTR) could be included in the preoperative cohort, but were excluded for the postoperative timepoints. Tumor sizes were measured on T1+Gd MRI images, using 3D Slicer software. Absolute (ATGV) and relative (RTGV) growth velocity were calculated between scans. ATGV was expressed as ml/day, RTGV as percentage of total tumor volume per day. Kruskal-Wallis and Wilcoxon signed-rank tests were used to compare TGV across three timepoints: before surgery, after the first surgery, and after the second surgery. RESULTS MRI scans of 37 patients were analyzed. Not every patient had data available for every timepoint (some had only 1 pre-operative scan, others had no postoperative follow-up scans). In the subgroup of 14 patients with data available for at least two timepoints , ATGV significantly decreased between the post-first-surgery and post-second-surgery periods (p = 0.047). RTGV demonstrated a near-significant decline (p = 0.084). In the total cohort, a decreasing trend in relative TGV was noted between the post-first-surgery and post-second-surgery periods, but without statistical significance (p = 0.095). Intra-patient analyses showed a consistent decrease in TGV after surgery. Spearman correlation showed volume dependency of ATGV, but not of RTGV. CONCLUSION Reduced TGV was observed after surgical resection, with the most pronounced decreases observed after a second resection in patients with longitudinal follow-up. The parallel findings for absolute and relative growth velocity suggest that this effect may not be explained solely by tumor volume reduction. These findings should be considered hypothesis-generating and require confirmation in larger prospective studies.