Sometimes called a Zimmerman's tumor, a phakomatous choristoma, is a very rare tumor that presents itself in infants. These tumors occur in the eyelid and and more rarely in the orbit of the eye. They are composed of proliferating, or growing, ocular lens (cuboida) tissue. The condition normally shows up before the baby is six months of age if it is going to appear at all. In some cases it is congenital and the baby is born with the tumor or tumors. The oldest patient ever recorded was thirteen months old. In most cases the tumor was located on or near the lower lid on the innermost part of the eye, sometimes obstructing the duct. All cases of these tumors have been benign and almost all of them were easily removed. Even in instances where the full tumor could not be removed the condition did not recur. There have only been about twenty cases reported, total.
A phakomatous choristoma will look like a slight, abnormal bulge in the eyelid. It will be hard to the touch and very similar to a dermoid cyst. They are composed of a densely fibrotic stroma creating the hard bulging tissue. They can also be accompanied by eosinophilic membrane-like material, psammoma body-like calcifications and intraluminal degenerated ghost cells. If present from birth they most often remain unchanged. The affected child's eye is typically normal and the tumor does not cause any problems aside from the bulge presenting itself.
It is possible that these tumors are sometimes misidentified as dermoid cysts or even cutaneous adnexal neoplasms or ocular adnexal oncocytomas. Dr. Lorenz Zimmerman first realized that they were not cysts and that they were abnormal lens tissue in 1971. Correct identification is important to avoid more aggressive excision methods. Unlike the similar lesions, phakomatous choristomas are extremely easy to remove.
What causes a phakomatous choristoma?
The exact cause of a phakomatous choristoma tumor is still unknown because it is so rare, but there are several theories that have been present to explain why they develop. They are possibly the result of the outmost layer of skin of the eyelid dipping downward too far while the eyelid is developing, resulting in abnormal cuboida tissue growth within the eyelid rather than just in the eye. It is also possible that during the development of the eye and the closing of the optic fissure, the lens migrates through it, resulting in abnormal eye development and the production of extra lens tissue that then grows separately in the lid. The last possible reason for growth of a phakomatous choristoma involves some of the lens tissue beginning to form inside out. That tissue then migrates toward the lower lid nearest the nose, growing there and forming a tumor.
From a histopathological perspective, the formation of a phakomatous chorisoma is very similar to congenital cataracts, but they form on the eyelid instead of directly in the eye. They are composed of the same tissue with neither cytokeratin nor epithelial membrane antigens. They both have very immunoreactive lens proteins.