Primary cerebellar pilocytic astrocytoma with anaplastic features: a case report

Introduction Pilocytic astrocytoma (PA), a grade I glioma, rarely occurs in adults sporadically. Presenting anaplastic features within PA are uncommon and we report such a patient. Case report A 57-year-old woman presented with headache and ataxia. Magnetic resonance imaging (MRI) of the brain showed a 3 cm heterogeneous-enhancing mass harbouring cystic component in the right cerebellar hemisphere. Histological examination of the tumour exhibited that it was mostly composed of compact piloid astrocytes and microcystic changes typical of PA with scattered eosinophilic granular bodies and Rosenthal fibres. Presence of coagulative necrosis, marked pleomorphism, focal vascular endo-thelial proliferation and multiple mitosis was consistent with anaplastic features. Ki-67 was 5% and p53 stained in >50% of cells. She received post-operative radiation therapy and the tumour relapsed 8 months later. Discussion The rarity of pilocytic astrocytoma in adults accounts for difficulties in diagnosing anaplastic features and distinguishing it from glioblastoma and degenerative PA. There are specific histological criteria for diagnosis of PA with anaplastic features including presence of coagulative/pseudopalisading necrosis, hypercellularity, cytological atypia and brisk mitotic activity in addition to typical features of PA. Studies show that such tumours, specifically when necrosis presents, behave in a more aggressive manner, analogous to grade III astrocytoma, but with better behaviour than grade IV astrocytoma.