LAUSR

Abstract Pilocytic astrocytomas rarely present with oligodendroglioma-like morphological features, which gives rise to a diagnostic challenge. In this report we present a case of pilocytic astrocytoma harboring the FGFR1 mutation, accompanied with a predominant oligodendroglioma-like component, thus initially diagnosed as oligodendroglioma. A 14-year-old female presented with syncope and simple partial seizure involving her right upper limb. Contrast-enhanced MRI revealed an enhancing lesion with substantial cystic portion and perifocal edema in the left parietal lobe. Open surgery was performed and a gross total resection of the tumor was achieved. On initial histopathological diagnosis, tumor cells with monotonous round nuclei and perinuclear halo predominated with branching capillaries, which were strongly suggestive for oligodendroglioma. Immunohistochemically, IDH1 R132H was negative, and Ki-67 index was around 5%. The patient was thus initially diagnosed as oligodendroglioma, WHO grade II, based on the 2007 WHO classification criteria. However, histopathological re-review revealed a minor astrocytic component with Rosenthal fibers and rare eosinophilic granular bodies, thus the diagnosis was changed as pilocytic astrocytoma. FGFR1 K654E mutation was confirmed by Sanger sequencing. Although she postoperatively developed mild sensory disturbance in her right hands, finger agnosia, and left-right disorientation, her symptoms had gradually improved, and she was discharged on day 17 with a Karnofsky performance status (KPS) of 90 and no cognitive decline. Without any adjuvant therapies, she has remained recurrence-free for 85 months. While the diagnosis of pilocytic astrocytoma with predominant oligodendroglioma-like component can be challenging, analysis of IDH1 and FGFR1 mutations can be beneficial in certain cases.