The Nature of Retinoblastoma. I. Photoreceptor Differentiation: A Clinical and Histopathologic Study

Current approaches to the diagnosis and management of retinoblastoma

• Six examples of a distinctive benign retinal tumor, occurring in five children and treated only by enucleation, were studied by light and electron microscopy and tested for S-100 protein, a glial-cell tissue marker. The small placoid, noninvasive lesions were composed entirely of benign-appearing cells with numerous fleurettes. These tumors showed no necrosis or mitotic activity. Ultrastructurally, they were composed predominantly of neuronal cells exhibiting photoreceptor differentiation. Some tumor cells had cytologic features of Muller's fibers and other glial cells that in one lesion stained positively for S-100 protein. In two patients there was a family history of retinoblastoma. All children were alive and well at follow-up examinations conducted three to 14 years after enucleation. To expand our concept of retinoblastoma to include this benign variant, we propose the term "retinocytoma." Although clinically and morphologically distinct from retinoblastoma, retinocytoma should carry the same genetic implication as its malignant counterpart.

Retinocytoma: A Benign Variant of Retinoblastoma

Tumors and tumorlike lesions of the globe and optic nerve in children represent a different histologic spectrum than in adults; the imaging appearances of these lesions reflect their pathologic features. Retinoblastoma is a tumor of infancy and the most common intraocular tumor in children. There are heritable and nonheritable forms. The most common clinical finding is leukocoria. The differential diagnoses of this sign include several nonneoplastic lesions: Persistent hyperplastic primary vitreous is a congenital persistence of an embryonic structure causing a retrolental mass. The primitive vasculature may produce a septum in the posterior chamber. Coats disease is a vascular malformation of the retina that produces a lipoproteinaceous subretinal exudate. The vascular malformation enhances with intravenous contrast material, and the fat-containing subretinal exudate does not. Larval endophthalmitis is a granulomatous reaction to the dead or dying larvae of Toxocara canis or T cati. The most important feature that allows differentiation of retinoblastoma from these so-called pseudoretinoblastomas is the presence of calcification in the former. Medulloepithelioma has two histologic forms; the teratoid type may contain calcifications, but it usually arises anteriorly from the ciliary body rather than posteriorly from the retina. Optic nerve glioma is the most common tumor of the optic nerve in children and is frequently associated with neurofibromatosis type 1. These gliomas are usually pilocytic astrocytomas and cause fusiform enlargement of the nerve.

https://pubs.rsna.org/doi/pdf/10.1148/rg.274075014

From the archives of the AFIP: Pediatric orbit tumors and tumorlike lesions: neuroepithelial lesions of the ocular globe and optic nerve.

Historic Review of Retinoblastoma

Differentiation of photoreceptor cell elements was observed in five retinoblastomas. These structures were studied by light and electron microscopy. Evidence of glial differentiation could not be found. The observations support the belief that the retinoblastoma is a distinctive neuronal neoplasm.

Lorenz E. Zimmerman

Papers

Photoreceptor Elements in Retinoblastoma: A Preliminary Report