Occurrence and distribution of pilomyxoid astrocytoma

Purpose. To know the occurrence and distribution of Pilomyxoid Astrocytomas amongst tumours previously diagnosed histologically as Pilocytic Astrocytoma and to assess the clinical impact of this new entity. Methods. Retrospective Diagnostic review of all cases histologically diagnosed as WHO Grade I Astrocytoma at a single Neurosurgical unit between 1990 and 2003. Results. Of a total of 91 cases identified, 9 were found to have Pilomyxoid histology. Of these, 8 were children (mean age 3.33 years) and 1 adult. 6 tumours were hypothalamochiasmatic in location. The clinical course of Pilomyxoid tumours was aggressive marked by maturation, multiple recurrences and disease control was rarely achieved with single treatment modality as opposed to typical pilocytics. The overall survival of the pilomyxoid group was not statistically different from the pilocytic tumours. Conclusions. Encompassing all age-groups and locations, Pilomyxoid Astrocytomas constitute about 10% of all tumours previously diagnosed as Pilocytic Astrocytoma. Nearly two-thirds are hypothalamo-chiasmatic in location. Knowledge of this entity is essential for appropriate aggressive treatment and follow-up.