A choristoma is a benign developmental proliferation of histologically mature tissue in an abnormal location. On the ocular surface, choristomatous lesions range from simple to complex forms.
Epibulbar dermoids are firm, dome-shaped, noncystic (solid) white-yellow nodules typically found at or straddling the limbus, most commonly in the inferotemporal quadrant (Fig 5-2A, B). Dermoids may occur in isolation or, particularly when bilateral, as a manifestation of a developmental syndrome such as linear nevus sebaceous syndrome (ie, an oculoneurocutaneous disorder) or Goldenhar syndrome (ie, oculoauriculovertebral dysgenesis). The latter is characterized by upper eyelid coloboma, preauricular skin tags, and vertebral anomalies in addition to epibulbar dermoid.
Dermolipomas are choristomas containing a substantial amount of mature adipose tissue, which makes them softer and yellower than dermoids. Like dermoids, dermolipomas may be associated with Goldenhar syndrome or linear nevus sebaceous syndrome. Unlike dermoids, dermolipomas occur more commonly in the superotemporal quadrant, toward the fornix; they may also extend posteriorly into the orbit.
The common histologic feature of epibulbar dermoids and dermolipomas is dense, obliquely arranged bundles of collagen in the substantia propria. Dermal adnexal structures are often present, and the surface epithelium may or may not be keratinized (Fig 5-2C, D). However, in dermolipomas, adipose tissue is present deep to the dense collagenous tissue in the stroma.
Clinically, complex choristomas are often indistinguishable from dermoids or dermolipomas. They may also be associated with linear nevus sebaceous syndrome. The histologic features of complex choristomas overlap with those of epibulbar dermoids or dermolipomas. However, complex choristomas contain other tissues such as bone (osseous choristoma), cartilage, lacrimal tissue, or neural tissue (Fig 5-2E). See also BCSC Section 6, Pediatric Ophthalmology and Strabismus.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.