INTRODUCTION Phakomatous choristoma, also known as Zimmerman's tumor, is a benign congenital adnexal hamartoma of lens tissue. It is seen at birth or shortly thereafter and three-fourths of patients are male. It likely develops from an abnormal migration of cells from the lenticular anlage into the mesodermal structures of the eyelid. Inferior cells of this presumptive lens tissue may become displaced as choristomatous elements into the embryonic mesenchyme destined to become the lower eyelid or anterior orbit. Alternatively, it may represent an additional locus of lens vesicle in the primitive surface ectoderm. The lesion may initially enlarge in an abortive attempt to form a lens.
CLINICAL PRESENTATION Phakomatous choristoma appears in newborns or in young children usually within the first few months of life and not associated with other developmental abnormalities. It presents as a circumscribed firm to rubbery subcutaneous mass in the medial lower eyelid near the inner canthus and can occasionally occur in or extend to the anterior orbit. They may range up to several centimeters in size. When large there may be concern about amblyopia or astigmatism.
(Courtesy of Stefan Seregard, M.D. Source: From Seregard S. Phakomatous choristoma may be located in the eyelid or orbit or both. Acta Ophthal Scand 1999; 77: 343-346, with permission of Wiley-Blackwell Publishing, Oxford, U.K.)
HISTOPATHOLOGY Within dense collagenous tissue are nests and irregular islands of polygonal epithelial cells having lightly eosinophilic cytoplasm and round to oval nuclei without nucleoli. The nests and islands of epithelial cells are surrounded by basement membrane material that stains positively with periodic acid-Schiff reagent (PAS stain), and thick strands of PAS-positive material often accumulate between cells (shown below on the right). Swollen epithelial cells may resemble "bladder cells" occurring in cataractous crystalline lenses, and brightly eosinophilic material resembling cataractous lens fibers forms pools within the epithelial islands. Dystrophic calcification and psammoma bodies may be present.
DIFFERENTIAL DIAGNOSIS The differential diagnosis should consider any mass lesion that can occur in the medial canthus of young children. These include dacryocystocele, dermoid cyst, adnexal neoplasms, or cutaneous carcinomas.
TREATMENT Since phakomatous choristomas are completely benign and frequently stable in size, aggressive and potentially damaging surgery to the lacrimal drainage system is not indicated. Excision is usually performed for diagnostic purposes to rule out more serious conditions. Conservative excision is warranted in most cases. Even when incompletely removed lesions do not recur.
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