Pilomyxoid astrocytomas with rare rosenthal fibers

Pilomyxoid astrocytomas (PMAs) were first officially described in 2007. Since then, intermediate pilomyxoid tumors with histopathological features typical of both PMAs and pilocytic astrocytomas (PAs) have been described. However, we found evidence of tumors that are histologically like PMAs but contain rare Rosenthal fibers, which have been reported in PAs but not in PMAs. We retrospectively analyzed four such cases involving a 16-year-old adolescent with a 3-cm recurring suprasellar tumor, an 11-year-old boy with a nonrecurring 3-cm mass in the left cerebellum, an 18-year-old adolescent with a mass in the suprasellar cistern who died 2 days after total tumor resection, and a 26-year-old woman with a nonrecurring 2-cm mass in the right temporal lobe. Microscopically, the tumors were a monomorphous population of small bipolar cells in a prominent myxoid/mucoid background with rare Rosenthal fibers. The tumor cells infiltrated the adjacent brain parenchyma. Findings for glial fibrillary acidic protein and oligodendrocyte transcription factor were positive, and the Ki-67 protein proliferation index was about 2 %. Our findings document the existence of tumors that are histologically like PMAs but also have Rosenthal fibers. Studies of more such cases are needed for clarification of such tumors’ clinical features.