8.4Scleral Tumors

Tumors of the sclera are exceptionally rare, but when they occur, they are usually the result of scleral extension of episcleral or conjunctival tumors; they also may appear secondary to intraocular or systemic neoplasms extending along vascular or neural intrascleral channels. Tumors of the episclera are more common than are tumors of the sclera; they may arise from episclera or from conjunctiva. Although some tumors have characteristic clinical appearance, diagnostic confirmation only can be obtained by biopsy.

The episclera and conjunctival tissues are composed of various elements, any one of which can form tumors. Examples of these elements and tumors are (1) epithelium (intraepithelial epitheliomas, carcinomas), (2) dense connective tissue (nodular fasciitis, fibromas, fibrous histiocytoma, sarcoma), blood and lymphatic vessels (angiomas, lymphangiomas), blood cells (leukemia, lymphoma, lymphosarcoma), nerves (neurofibroma, neurilemoma), and melanocytes (nevus, melanocytoma). Dermoid choristomas are composed of elements not normally present at the episclera or conjunctiva.

Episcleral and scleral tumors pose a challenge to the ophthalmologist, since they can be easily mistaken for inflammatory abnormalities of the episclera and sclera.

8.4.1Dermoid Choristomas

Epibulbar choristomas are easy to diagnose if they appear at the limbus in very young infants; however, choristomas occurring in the conjunctiva, episclera, or sclera are difficult to distinguish from other tumors. Epibulbar episcleral choristomas, usually occurring in the lower temporal quadrant, are characterized by isolated solid or cystic nodules of variable size which are adherent to the bulbar conjunctiva or to the sclera. They result from inclusions of epidermal and connective tissue at sites of closure of the fetal clefts which grow from birth and have a burst of activity at puberty; the connective tissue is covered by

stratified epithelium with keratin, hair follicles, and sebaceous glands [118].

Episcleral osseous choristomas usually occur in the upper temporal quadrant 5–10 mm behind the limbus [163] and are characterized by isolated nodules of variable size which are either freely moveable or adherent to the conjunctiva or to the sclera. They can grow very large. Although most of them are composed of mature bone, occasionally cartilage may be found; [164, 165] bone or cartilage are surrounded by connective tissue with other choristomatous elements, such as meningothelial cells or hematopoietic marrow [163, 166].

Episcleral lipodermoids (dermolipomas) are solid tumors which contain fatty tissue. They are true choristomas, since fatty tissue is not normally present anterior to the orbital septum. They are usually located laterally and may extend into the orbit. Since the excision is only for cosmetic reasons, only the superficial layer of the tumor must be removed.

8.4.2Epithelial Tumors

8.4.2.1 Papillomas or Intraepithelial Epitheliomas

Epithelial tumors of the conjunctiva, including papillomas or intraepithelial epithelioma (Bowen’s disease), tend to occur at the limbus, are confined to the superficial conjunctival layers without episcleral invasion, and ulcerate into the surface [38]. Occasionally, however, papillomas or epitheliomas can grow away from the limbus and deeply invade the episclera and sclera.

8.4.2.2 Squamous Cell Carcinoma

Intraocular invasion by squamous cell carcinoma of the conjunctiva may manifest as necrotizing scleritis, sometimes with scleral perforation and uveal prolapse [167–169]. Necrotizing scleritis appears adjacent to an enlarging, vascularized, elevated, conjunctival mass, close to the limbus. Diagnosis of the tumor is achieved after excisional biopsy of the mass. Squamous cell carcinomas have been associated with acquired immunodeficiency syndrome (AIDS), AIDS-related complex,