Ocular Pathology

Anatomy and pathology of the human eye. Use it to review eye pathology for Ophthalmology Board Review or OKAP.

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Saturday, March 04, 2006

What is a phakomatous choristoma?

Definition: Phakomatous choristoma is considered a lens anlage tumor described in 1971 by Zimmerman (also coined Zimmerman’s tumor). The tumor is formed of proliferating tissue that recapitulates the lens in development. It may occur in the eyelid or orbit.

Epidemiology: The tumor occurs in infants and generally presents prior to 6 months of age (mean age at surgery=6.3 months). The oldest patient reported was operated at 13 months.

Etiology: Theories of pathogenesis include
1. surface ectoderm "dipping down" into the mesoderm of the developing eyelid,
2. migration of putative lens tissue through the closing optic fissure, and
3. the site of origin of the invaginating lens being located in the area destined to form the nasal lower lid
Histopathology: The tumor is composed of cuboidal (lens type) epithelium (#2 in the figure) that forms ducts in a fibrous stroma. There is exuberant basement membrane material reminiscent of lens capsule. This basement membrane material (recapitulating the lens capsule) lines the external surface of most of the ducts (arrowheads at 4 enclose). In addition the ducts may contain in their lumen proteinaceous material that include lens crystallins (#3 in figure). In addition you may be able to find calcific foci in the stroma (#1 in the figure). The basement membrane material is PAS positive and characteristic. There may be degenerate areas reminiscent of the Wedl or "bladder-like" cells of cataract. Previously reported cases have shown immunohistochemical staining for lens crystallins and ultrastructural appearances that feature interdigitating plasma membranes (folded plasmallema).
Clinical: Only about 20 cases have been reported in the literature and most are located in the inferior nasal aspect of the eyelid but at least one has been reported primarily in the orbit. One of the previously reported cases had a colobomatous hypoplastic optic disc with staphyloma, and severe myopia suggestive of abnormality of closure of the optic fissure. Other cases showed astigmatism or epiphora attributable to eyelid lesions that resolved postoperatively.
Prognosis: The cases in the literature have all behaved quite benignly. In fact even tumors that were incompletely excised (2) did not recur.

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