The fine structure of choroid plexus carcinoma.

The ultrastructural findings of two cases of choroid plexus carcinoma occurring in infants 11 and 24 months old are discussed. Both had a similar ultrastructural pattern which demonstrated a clear polygonal cytoplasm, cell polarity towards the lumina, junctional complexes and evidence of a basement membrane, all of which point to an epithelial origin for the proliferating cells. Abundant immature cellular characters such as polyribosomes, glycogen granules and hypertrophied rough endoplasmic reticulum were found. The importance of the differential diagnosis from ependymoblastoma and benign choroid plexus papilloma is emphasized. In the former, the major differentiating features are the existence of abundant glial neuropil and cellular characters of glial differentiation, whilst in the latter, cytoplasmic features demonstrate cellular maturity.