[Choroidal epithelial cyst of the quadrigeminal plate]

A case of choroidal epithelial cyst of the quadrigeminal plate is reported. A twenty-five-year-old man was admitted to our department because of Parinaud's sign and intermittent headache. CT and MRI showed a cyst in the posterior part of the third ventricle. Left occipital transtentorial approach was carried out and the wall of the cyst was subtotally removed. The cyst contained watery clear fluid. On light microscopy, the cyst wall consisted of a single layer, flat epithelial cells and thick collagenous connective tissue. An electronmicroscopic study revealed that the epithelial cells rested on a basement membrane separating them from the underlying collagenous tissue. Microvilli without coating material were presented on the surface of the cells. With this data in hand, the cyst was considered to originate from the developing choroid plexus.