ATYPICAL CHORISTOMATOUS CYSTS OF THE ORBIT

Background: The commonest choristomatous cysts of the orbit are dermoi d and epidermoid cysts, which are lined by kerantinizing squamous epit helium. They typically occur in the superior orbit, most commonly supe rotemporally. Other types, lined by different epithelia, and other orb ital sites are much less common.Methods: Five cases of atypical orbita l cystic choristomas that presented over the part 6 years are reported . The clinical and radiological features, surgical approach and findin gs, and histology are described. Similar cases from the literature are reviewed, and possible aetiology discussed. Results: Four of the cyst s were lined by a non-keratinizing epithelium resembling conjunctiva; two had adnexal structures in their walls. Compared with typical dermo id and epidermoid cysts, these 'conjunctival dermoids' and 'conjunctiv al cysts' of the orbit tended to present later in life, none were asso ciated with bony defects, and three of the four occurred in the supero medial quadrant. One case occurred inferiorly, a rare site for orbital conjunctival dermoids and cysts, or typical dermoids and epidermoids. The fifth case, also inferior is an example of a cyst within choristo matous lacrimal tissue. Conclusion: Choristomatous cysts of the orbit may occur with non-keratinizing epithelial linings, and such cysts ten d to differ clinically from the commoner dermoids and epidennoids. The y may also occur in atypical sites such as the inferior orbit.