The pilomyxoid astrocytoma and its relationship to pilocytic astrocytoma: report of a case and a critical review of the entity.

Pilomyxoid astrocytoma (PMA) is a rare glioma that shares histopathological similarities with pilocytic astrocytoma (PA). Yet, typical examples of both can be distinguished on clinical and histological grounds. The reported aggressive behavior of PMA provides a rationale for distinguishing this entity from typical PA. We report a 6(1/2) -year-old girl who had suffered poor weight gain, irritability and progressively worsening abnormal eye movements since approximately 2 months of age. Radiographic studies at 6 months of age (age at initial presentation) revealed a large hypothalamic lesion occupying proximal portions of the optic nerves, chiasm and right posterior optic tract. The first biopsy obtained after two chemotherapy regimens was consistent with a diagnosis of PMA. The patient suffered multiple recurrences, and underwent three subsequent surgical procedures. The last two surgical specimens revealed a tumor with histopathological features of PA. She is alive with residual disease 6 years after initial presentation. While earlier studies focused on the similarities between PA and PMA, considering the latter as the "infantile" form of the former, subsequent work outlined their histological and clinical differences. Some even suggested a different cell type, such as the tanycytic cell as the origin for PMA. This report provides evidence in favor of the earlier argument that there is a close relationship between PA and PMA, and presents a rare "maturation" phenomenon, at least from a morphological perspective. More systematic review of such cases will provide a better answer for the origin of PMA, and its relation to PA.