Epithelial rests found at sutural sites within the orbit can give rise to epithelial cysts. Cysts of the surface epithelium are further divided into simple epithelial cysts (epidermal, conjunctival, respiratory and apocrine gland), and dermoid cysts (epidermal and conjunctival). Epidermal dermoid cyst (dermoid) is by far the most common orbital cystic lesion in children, accounting for over 40% of all orbital lesions of childhood. Other developmental cysts are teratomatous cysts, neural cysts (congenital cystic eye and colobomatous cyst) and those associated with brain and meningeal tissue (encephalo-cele and optic nerve meningocele) . Developmental cysts have to be differentiated from secondary cysts, like mucocele and inflammatory cysts. Mucocele can occur in children with cystic fibrosis. Inflammatory cysts are generally due to parasitic infestations and are more common in tropical areas of the world. Furthermore, non-cystic tumourous lesions with a cystic component (like rhabdomyosarcoma and lymphangioma) can present as a cyst.
Optic nerve and meningeal tumours can spread into the orbit. Together they represent 8% of all orbital tumours.
The orbit is the most common location for metastases to the eye and adjacent structures in children (neuro blastoma), whereas the choroid is the predominant site in adults. Approximately 5% of all orbital tumour-like lesions are metastatic lesions. However, because malignancies are far more frequent in adults, most orbital metastatic lesions are found in elderly patients. The mean period of time between the onset of the primary disease and orbital manifestation is 5 years. The main primary symptoms are lid swelling, red eye, diplopia and proptosis. The most frequent primary tumour is a breast carcinoma, but many other carcinomas can metastasise to the orbit (Figs. 10.31, 10.32). Metastatic melanomas to the eye and orbit are rare and generally occur in patients with disseminated metastases during the terminal stages of the disease, with a short life expectancy.
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