Medulloepithelioma is a neuroepithelial tumor arising from primitive medullary epithelium (ie, the inner layer of the optic cup). This tumor usually arises from the ciliary epithelium but has been documented in the retina and optic nerve in rare instances. In the ciliary body, medulloepithelioma may appear clinically as a lightly pigmented or white cystic mass with erosion into the anterior chamber and iris root (see Chapter 19, Fig 19-15). Within the tumor, undifferentiated round-to-oval cells with little cytoplasm are organized into ribbonlike structures that have a distinct cellular polarity (Fig 11-49). Cell nuclei are stratified in 3–5 layers, and the entire structure is lined on one side by a thin basement membrane. One surface secretes a mucinous substance, rich in hyaluronic acid, that resembles vitreous. Stratified sheets of cells are capable of forming mucinous cysts that are clinically characteristic. Homer Wright and Flexner-Wintersteiner rosettes may also be present.
Medulloepitheliomas that contain solid masses of neuroblastic cells indistinguishable from retinoblastomas are more difficult to classify. Heteroplastic tissue, such as cartilage or smooth muscle, may be found in medulloepitheliomas. This variant of the tumor, composed of cells from 2 different embryonic germ layers, is referred to as teratoid medulloepithelioma. Medulloepitheliomas that have substantial numbers of undifferentiated cells with high mitotic rates and demonstrate tissue invasion are considered malignant; however, patients treated with enucleation have high survival rates, and “malignant” medulloepithelioma typically follows a relatively benign course if the tumor remains confined to the eye.
A, Low-magnification photomicrograph of Fuchs adenoma (asterisk) arising from the nonpigmented ciliary body epithelium (arrow). Note the pigmented layer of the ciliary body epithelium surrounding the tumor. B, High magnification reveals interweaving trabeculae of bland nonpigmented ciliary epithelial cells surrounding eosinophilic hyaline material.
(Courtesy of Nasreen A. Syed, MD.)
In rare cases, ciliary body medulloepithelioma presents in association with pleuropulmonary blastoma as part of a familial tumor syndrome. In these cases, tumors are typically secondary to a germline mutation in the DICER1 gene.
Schultz KA, Yang J, Doros L, et al. DICER1-pleuropulmonary blastoma familial tumor predisposition syndrome: a unique constellation of neoplastic conditions. Pathol Case Rev. 2014;19(2):90–100.
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.