To evaluate the clinical features of developmental cysts of the orbit. Retrospective study of patients who had excision of cysts between 1992 and 2020. Three hundred and 58 patients (189 male; 53%) with orbital developmental cysts were identified, all being unilateral. Age at surgery varied from birth to 77 years (mean 17, median 18 years) and the average symptom duration was 5 years (median 18 months; range 1 day-50 years). The commonest presenting features were a peribulbar lump or upper lid swelling, followed by proptosis, pain, diplopia and reduced vision. Most patients (82%) had a palpable mass, with epidermoids, sebaceous dermoids and keratinised dermoids commonly affecting the superotemporal quadrant, and conjunctiva-containing cysts usually being biased to a medial location. Cysts were lined by keratinised epithelium with dermal structures (224/358; 63%), non-keratinised epithelium with dermal structures (69/358; 19%), epidermis without identifiable dermal structures (19/358 'epidermoids'; 5%), conjunctiva (12/358; 3%), respiratory epithelium (4/358; 1%), or mixed dermal and conjunctival epithelia (30/358 'dermo-conjunctival' cysts; 8%). Overall, two-thirds (242/358; 66%) had histological evidence of chronic intramural inflammation, and a half of cysts showed granuloma formation (178/358 cysts). Chronic inflammation was less common with conjunctival cysts (54%, 7/12 patients) and none showed granuloma formation. Developmental cysts of the orbit vary from the relatively common dermoid cysts to the extremely rare respiratory epithelial-lined cysts. Respiratory cysts, being deeper, may present late in life and cysts containing conjunctival epithelium tend to be less inflamed and typically favour the superonasal quadrant.
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