Phakomatous choristoma is a rare lesion that generally occurs on or near the eyelid and is often mistaken as a cyst or other type of lesion (or tumor). The lesion is usually congenital, which means that it is present at birth, though it may not be apparent until shortly after birth. Phakomatous choristoma is also known as Zimmerman’s tumor, named for the first person who described it in 1971. The tumor is benign, meaning that it does not lead to cancer, and according to the Diagnostic Atlas of Common Eye Diseases it is more common among males.
Causes of phakomatous choristoma
The origin of the cells that contribute to the growth was suspected, based on microscopic investigations, to be the lens since the lesion's discovery. Histological studies, such as that carried out by Lee et al. in 2004 (published in Ophthalmology), have found that the tumor expresses lens-specific proteins, including crystalline, confirming the suspicions about its origin. Lee at al. also identified that it is a lens fiber tumor, rather than a lens epithelium tumor, though more recent reports refer to the bladder cell-like appearance of swollen epithelial cells in the mass.
It is thought that fibrous stromal cells from the lens proliferate, enlarging to create the mass. The origin of the cells outside the lens is due to some of the lens cells migrating to the eyelid or surrounding structures, such as the ocular orbit, during embryonic development, which may be the underlying cause of their inappropriate growth and proliferation.
Treatment of phakomatous choristoma
When a Zimmerman’s tumor is present, doctors use imaging to determine the boundaries of the lesion, and then it is surgically removed. Histology and immunochemistry can then be performed to confirm the diagnosis. Because this is such a rare tumor, with approximately 20 cases reported in the literature according to Benshek and Leatherbarrow in their 2005 comment to the British Journal of Ophthalmology, there is no established guideline for the diagnosis or treatment of the lesion. However, a phakomatous choristoma generally appears as a firm or rubbery subcutaneous mass in the lower eyelid. However, a few cases of the lesion occurring in the eye socket or obstructing the lacrimal-nasal duct have been reported.
The lesion is generally not associated with complications after removal as long as the surgery is conservative and avoids damage to the lacrimal ducts. Benshak and Leatherbarrow were the first to report other eye conditions in the presence of a phakomatous choristoma. They suspect that the etiology of the lesion, that is, at what point in development and why exactly it formed, determines whether additional cases will present with similar problems.
Prognosis of Zimmerman’s tumor
This rare lesion is not well studied because of its infrequent occurrence, but the cases reported to date have had good prognoses and outcomes. The lesion is surgically removed mainly for diagnostic purposes, and very few associated complications have been reported. Because the mass is caused by inappropriate migration and proliferation of lens cells during development, the tumor cannot be prevented, but it is easily treated once its appearance is recognized.