"Atypical choroid plexus papillomas are considered WHO grade 2 tumours in the 2021 WHO classification of CNS tumours 2. They are distinguished from choroid plexus papillomas primarily on the basis of increased mitotic activity (≥2 mitoses per 10 high-power fields; choroid plexus carcinomas have ≥5 mitoses per 10 high-power fields) 1."