Retinocytoma is a rare, highly differentiated retinoblastic tumor. The pathogenesis of this variant is the subject of debate. Some authors contend that the tumor is a fully differentiated form of retinoblastoma, whereas others argue that it is the benign counterpart of retinoblastoma. Retinocytoma is characterized histologically by numerous fleurettes admixed with individual cells that demonstrate varying degrees of photoreceptor differentiation (Fig 11-48). Retinocytoma differs from retinoblastoma in the following ways:
retinocytoma cells have more cytoplasm and more evenly dispersed nuclear chromatin
mitoses are not observed in retinocytomas
although calcification may be identified in retinocytomas, necrosis is usually absent
Retinocytoma should be distinguished from the spontaneous regression of retinoblastoma that is the end result of coagulative necrosis. See the discussion in Chapter 19.
Figure 11-46 Retinoblastoma optic nerve invasion. A, Gross examination of the globe reveals a large intraocular tumor in the posterior segment with bulbous enlargement of the optic nerve (arrow) caused by direct extension. B, Retinoblastoma has invaded the optic nerve and has extended posterior to the lamina cribrosa to the margin of surgical resection (arrow).C, Cross section through the optic nerve shows tumor (arrows) present at the surgical cut end (surgical margin). This finding portends a poor prognosis.
(Parts B and C courtesy of Nasreen A. Syed, MD.)
Figure 11-47 Retinoblastoma with the high-risk histologic feature of massive choroidal invasion (between arrowheads). Massive choroidal invasion is defined as an invasive focus of tumor with a diameter (in any dimension) of least 3 mm and a choroidal focus of tumor that reaches at least the inner fibers of the scleral tissue.
(Courtesy of Nasreen A. Syed, MD.)
Figure 11-48 Retinocytoma. Note the significant degree of photoreceptor differentiation with apparent stubby inner segments (arrow).
Figure 11-49 Medulloepithelioma. Photomicrograph shows a ciliary process (between arrows) surrounded by ribbons, cords, and small sheets of blue tumor cells with pockets of vitreous (asterisks) and occasional Flexner-Wintersteiner rosettes (arrowhead).
(Courtesy of George J. Harocopos, MD.)
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.