Choroid plexus carcinomas show papillary architecture in better differentiated foci (as shown in this image). Poorly-differentiated areas are generally solid and composed of highly atypical cells arranged in sheets. The hallmarks of malignancy include at least 4 of the following features: nuclear pleomorphism, >5 mitoses/10 HFP, increased cellularity, necrosis, solid architecture, and invasion of brain parenchyma. Most cases of choroid plexus carcinoma are seen in children and they usually present before 3 yrs. of age.