Tumeurs perlées, as described by Cruveilhier1 in 1829, are among the more rare intracranial neoplasms, comprising less than 1 per cent of the total number of the latter. The use of the term dermoid or epidermoid2 is preferable to that of cholesteatoma, as it indicates the epithelial nature of the tumors and distinguishes them from the "cholesteatomas" of middle ear origin. Their lustrous "mother-of-pearl" appearance makes them easy to recognize. Not infrequently they are cystic.
Epidermoids differ from dermoids in that they contain only squamous or basal epithelium, while dermoids also have epithelial appendages, such as hair and sebaceous glands. Approximately 150 cases of pearly tumors have been reported in the literature; the location was chiefly in the pia mater at the base of the brain. Chiasmal syndromes occur; the tumor may extend into the cerebellopontile angle, or, as in 2 of Cushing's cases reported by Bailey,3