Ancillary Imaging
In the initial staging EUA, patients with retinoblastoma may receive fundus photography, fluorescein angiography (FA), handheld optical coherence tomography (OCT), and B-scan ultrasonography. Results of color fundus photography enable documentation of the appearance and location of retinal tumors and the sites of vitreous and subretinal seeding; serial images over time are helpful for determining treatment efficacy and disease recurrence. Common findings of retinoblastoma on FA include retinal vascular dilatation, capillary telangiectasia, intrinsic tumor vessel formation, and retinal venous leakage; subclinical iris neovascularization may also be seen.
In eyes with small tumors or a visible macula, OCT with a handheld device can be helpful in assessing macular anatomy and in identifying and monitoring retinal tumors. Small retinoblastoma tumors are smooth, round, cream-colored, homogeneous, and isodense on OCT. Small tumors may involve the inner nuclear layer (INL) and the outer nuclear layer (ONL), whereas very small tumors have been described as limited to the ONL, with draping of the overlying inner retinal layers beginning with the outer plexiform layer (Fig 19-8). So-called invisible tumors that are very early may be detected on OCT before ophthalmoscopic visualization is possible. OCT also can be used to evaluate the extent and morphology of vitreous seeds (Fig 19-9). Ultrasonographic findings of a dome-shaped retinal lesion with scattered intratumoral calcifications are critical for diagnosing retinoblastoma, particularly when ophthalmoscopic visualization of the tumor is limited (Fig 19-10). Results of EUA are used to classify each eye, as discussed in the Retinoblastoma Classification section. The group classification is useful in determining therapeutic options, visual prognosis, and potential for ocular salvage.
Retinoblastoma may invade the optic nerve head and spread through the lamina cribrosa into the central nervous system (CNS). Rarely, in bilateral cases, retinoblastoma can be associated with a separate CNS tumor called a pinealoblastoma (a condition referred to as trilateral retinoblastoma; Fig 19-11). Hence, imaging studies of the optic nerve, orbits, and brain are essential for complete staging of a child with retinoblastoma. Magnetic resonance imaging (MRI) is the preferred diagnostic modality for this purpose. MRI enables better soft-tissue resolution than does computed tomography (CT) and does not expose the patient to potentially harmful radiation, which is especially important in children with a genetic cancer syndrome (see the Genetic Counseling section). Aside from MRI of the brain, systemic metastatic evaluation with bone marrow and lumbar puncture is not indicated in children without neurologic abnormalities or evidence of extraocular extension. If extension of the retinoblastoma into the retrobulbar optic nerve is suspected, lumbar puncture and bone marrow biopsy may be performed as part of the workup, but they should not delay definitive enucleation or neoadjuvant chemotherapy.
In the United States, patients rarely present with metastases or intracranial extension at the time of diagnosis; in contrast, advanced presentations are common in resource-limited countries. The most frequently identified sites of metastatic involvement in children with retinoblastoma are the orbit, brain, distal bones, lymph nodes, skull bones, spinal cord, and abdominal viscera. Retinoblastoma cells may escape the eye by invading the optic nerve and extending into the cerebrospinal fluid. In addition, tumor cells may massively invade the choroid before traversing emissary canals, thereby spreading hematogenously or eroding through the sclera to enter the orbit. Extraocular extension may result in proptosis as the tumor grows in the orbit (Fig 19-12). In the anterior chamber, tumor cells may invade the trabecular meshwork, gaining access to the conjunctival lymphatics. Subsequently, palpable preauricular and cervical lymph nodes may develop.
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Kim JW, Ngai LK, Sadda S, Murakami Y, Lee DK, Murphree AL. Retcam fluorescein angiography findings in eyes with advanced retinoblastoma. Br J Ophthalmol. 2014;98(12):1666–1671.
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.