Atypical choroid plexus papilloma

Last revised by Assoc Prof Frank Gaillard on 19 Oct 2021

Atypical choroid plexus papillomas are WHO grade 2 tumors derived from choroid plexus epithelium with intermediate clinical and pathological features between more indolent choroid plexus papillomas and more aggressive choroid plexus carcinomas.

As clinically, and on imaging, they are difficult to distinguish from choroid plexus papillomas and therefore their description is not repeated here. 

Pathology

Atypical choroid plexus papillomas are considered WHO grade 2 tumors in the current (2021) WHO classification of CNS tumors 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

Other features that may be present include 1:

  • increased cellularity
  • nuclear pleomorphism
  • more solid growth pattern with blurring of papillary pattern
  • necrosis

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