Note the orderly arrangement of epithelial cells around fibrovascular cores. Cytologic atypia is absent and mitotic activity is not increased. Choroid plexus papillomas are low-grade tumors (WHO Grade 1) and cured by total resection (100% 5-yr survival). The differential diagnosis in children includes papillary ependymoma and this distinction may be difficult in some cases. In older patients, metastatic papillary carcinomas should be ruled out. Choroid plexus papillomas with at least 2 mitotic figures/ 10 HPF are defined as Atypical Choroid Plexus Papillomas (WHO Grade II tumor). They may also contain areas of hypercellularity, cytologic atypia, and necrosis.