An unusual fibro-osseous component in intracranial lesions

An unusual fibro-osseous component has been identified in intracranial lesions. Ultrastructurally this component appears to represent stages of membranous bone formation, but of an atypical and incomplete sort. The fibroosseous component may be an aberrant type of bony metaplasia and is seen in several lesions all of which probably do not share the same etiology although in each case meningeal or choroid plexus stroma appears to be involved.