Figure 8-8 A calcific plaque of the sclera. A, Calcific plaques (arrow) are typically located just anterior to the insertion of the medial and lateral rectus muscles. B, Basophilic calcific deposits are noted in the sclera (arrowheads) anterior to the rectus

muscle insertion (arrow). (Part A courtesy of Vinay A. Shah, MBBS; part B courtesy of Tatyana Milman, MD.)

Scleral Staphyloma

Scleral staphylomas are scleral ectasias that are lined internally by uveal tissue and that may occur at points of weakness in the scleral shell, either in inherently thin areas (such as posterior to the rectus muscle insertions; Fig 8-9) or in areas weakened by tissue destruction (as in scleritis; see Fig 8-7). In children, staphylomas may occur as a result of long-standing increased intraocular pressure or axial myopia, owing to the relative distensibility of the sclera in the young. Location and age at onset, therefore, vary according to the underlying etiology. Histologic examination invariably reveals thinned sclera, with or without fibrosis and scarring, again depending on the cause.

Neoplasia

Neoplasms of the sclera are exceedingly rare. Tumors originate predominantly in the episclera or Tenon capsule rather than in the sclera proper.

Figure 8-9 Scleral staphylomas. Several regions of scleral thinning (arrows), which appear blue because of the underlying uveal tissue, are present posterior to the rectus muscle insertions (arrowheads) and in the equatorial sclera. (Courtesy of

Nasreen A. Syed, MD.)

Fibrous Histiocytoma

Fibrous histiocytoma, also known as fibroxanthoma or fibrohistiocytic tumor, is a benign soft-tissue tumor with fibrous differentiation, formed by a proliferation of fibrocytes and histiocytes, characteristically in a whorled (storiform) pattern (see Chapter 14, Fig 14-11). Though more common in the orbit, it may occasionally involve the sclera, particularly the corneoscleral limbus (Fig 8-10). Malignant fibrous histiocytoma (atypical fibroxanthoma) of the corneoscleral limbus demonstrates increased mitotic activity, nuclear pleomorphism, necrosis, and an invasive growth pattern. Although malignant fibrous histiocytoma of the corneoscleral limbus can be locally aggressive, the tumor generally does not metastasize.

Figure 8-10 Fibrous histiocytoma of the corneoscleral limbus. A, A gelatinous, gray, vascularized, dome-shaped nodule extends into the corneal stroma. B, Microscopic evaluation reveals a proliferation of spindle fibroblasts, rounded histiocytes, and occasional multinucleated giant cells (arrow); scattered lymphocytes are also seen (arrowheads). (Part A courtesy of Ira J.

Udell; part B courtesy of Tatyana Milman, MD.)

Nodular Fasciitis

Nodular fasciitis is a reactive process that may, in rare instances, cause a tumefaction in the episclera. The disease usually affects young adults as a rapidly growing, round to oval, firm white-gray nodule that measures 0.5–1.5 cm and appears at the limbus or anterior to a rectus muscle insertion. Antecedent trauma has been implicated as an etiologic factor for the development of nodular fasciitis in other body sites, but such an association is infrequent in the sclera. Though self-limited, nodular fasciitis is usually excised because of its rapid growth.

Histologic examination reveals a circumscribed spindle cell proliferation in which the appearance of individual cells resembles that of fibroblasts growing in tissue culture. These spindle cells aggregate in short fascicles, admixed with a chronic inflammatory infiltrate, in a vascular, myxoid stroma (Fig 8-11). Older lesions may show foci of dense collagen deposition. Although mitotic figures may be present, unbalanced (eg, tripolar) mitoses are absent. Because of the cellular nature of these proliferations and the presence of mitotic figures, nodular fasciitis may be misinterpreted histologically as sarcoma (soft-tissue malignancy), a pitfall to avoid.

Figure 8-11 Nodular fasciitis. Activated spindled fibroblasts are loosely arranged in short fascicles (between arrowheads). A prominent capillary network (arrows) and chronic inflammatory infiltrate are also observed.