Ependymomas 
– most cases present in children < 10 years old and are located in the 4th ventricle 
– will have prominent perivascular pseduorosettes (fibrillary processes surrounding a vessel, creating a clearing between the tumor nuclei and the blood vessel) 

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Medulloblastomas present in the 4th ventricle as well but will typically have hypercellular, tightly packed neoplastic cells and Homer-Wright rosettes