OBJECTIVE: Pilocytic astrocytoma (PA) is a common type of pediatric brain tumor that can arise within the hypothalamic/chiasmatic region and typically has an excellent outcome. We identified a group of tumors, previously classified as PAs, with unique histological features and aggressive behavior. This article describes the clinicopathological features of these unusual neoplasms, which are currently known as pilomyxoid astrocytomas (PMAs), to better differentiate them from typical PAs.
METHODS: Medical information and surgical specimens were obtained for 42 PA cases and 21 PMA cases. Patient demographic features, treatment modalities, progression-free survival (PFS) times, overall survival (OS) times, and outcomes were compared between the groups with nonparametric tests.
RESULTS: The PMA group included 12 male and 9 female patients. The PA group included 27 male and 15 female patients. The mean ages at diagnosis for the PMA and PA groups were 18 months (range, 2–84 mo) and 58 months (range, 4–189 mo), respectively (P < 0.01). The mean PFS times for the PMA and PA groups were 26 and 147 months, respectively (P < 0.001). The mean OS times for the PMA and PA groups were 63 and 213 months, respectively (P < 0.001). Sixteen patients with PMAs (76%) experienced local recurrence, and three of those patients demonstrated evidence of cerebrospinal fluid dissemination. Twenty-one patients with PAs (50%) experienced local recurrence, none with evidence of cerebrospinal fluid dissemination. Within the follow-up period, seven patients with PMAs (33%) and seven patients with PAs (17%) died as a result of their disease. In an age-matched set, the mean PFS times for the PMA and PA groups were 25 and 163 months, respectively (P < 0.01), and the mean OS times for the PMA and PA groups were 60 and 233 months, respectively (P < 0.001).
CONCLUSION: Hypothalamic/chiasmatic PMAs occurred in a significantly younger population and were associated with substantially shorter PFS and OS times than were typical PAs. Increased recognition of these lesions could affect the prognosis and treatment of pediatric astrocytomas.