Postoperative imaging surveillance in pediatric pilocytic astrocytomas

Currently there is no consensus regarding the frequency of neuroimaging following gross-total resection (GTR) of pilocytic astrocytoma (PA) in children. Whereas several reports recommend no postoperative imaging, one study proposed surveillance MR imaging studies to detect delayed recurrences.

The records of 40 consecutive pediatric patients who underwent GTR of infratentorial PAs were examined. All had follow-up duration of ≥ 2 years. Patients underwent early (< 48 hours) postoperative MR imaging, followed by surveillance imaging at 3-6 months, 1 year, and variably thereafter. The classification of GTR was based on a lack of nodular enhancement on early postoperative MR imaging. Demographic, clinical, and pathological variables were analyzed with respect to recurrence status. Univariate and multivariate analyses were performed to evaluate the association between pathological variables and recurrence-free survival (RFS).

Of 13 patients demonstrating new nodular enhancement on MR imaging at 3-6 months, the disease progressed in 10, with a median time to recurrence of 6.4 months (range 2-48.2 months). At last follow-up, 29 patients had no recurrence, whereas in 1 additional patient the tumor recurred at 48 months, despite the absence of a new contrast-enhancing nodule at 3-6 months (for a total of 11 patients with recurrence). No demographic variable was associated with recurrence. Nodular enhancement on MR imaging at 3-6 months was significantly associated with recurrence in both univariate (p < 0.0001) and multivariate (p = 0.0015) analyses. Among the pathological variables, a high Ki 67 labeling index (LI) was similarly significantly associated with RFS in both univariate (p = 0.0016) and multivariate (p = 0.034) analyses. Multivariate models that significantly predicted RFS included a risk score incorporating Ki 67 LI and CD68 positivity (p = 0.0022), and a similar risk score combining high Ki 67 LI with the presence of nodular enhancement on initial surveillance MR imaging (p < 0.0001).

Surveillance MR imaging at 3-6 months after resection predicts tumor recurrence following GTR. One patient suffered delayed recurrence, arguing against a "no imaging" philosophy. The data also highlight the pathological variables that can help categorize patients into groups with high or low risk for recurrence. Larger series are needed to confirm these associations.