Can Enhancement Pattern in Normal Sized Optic Nerves on MRI Better PredictTumor Invasion in Retinoblastoma Eyes?

INTRODUCTION:Optic nerve enhancement alone without optic nerve thickening on CE-MRI can be associated with post-laminar optic nerve invasion (PLONI) in eyes with group E retinoblastoma. A few case reports and retrospective studies in the literature show a poor correlation between optic nerve enhancement on MRI and optic nerve invasion on histopathological examination (HPE). There is no universal consensus on the management of such cases. It is desirable that the presence and extent of a true optic nerve invasion are reliably picked up before planning upfront enucleation in order to avoid stage II disease. METHODS:In a prospective study conducted at a tertiary eye care center in North India, all retinoblastoma patients presenting with optic nerve enhancement on imaging were evaluated. Demographic and imaging details, histopathological findings, and treatment details were recorded. Length and pattern of enhancement noted on MRI were correlated with histopathology. Follow-up was done till the end of the study period.RESULTS:Six Group E retinoblastoma eyes were evaluated. 3 eyes (50%) showed solid enhancement, 2 eyes (33.33%) had tram track pattern and 1 eye showed (16.66%) punctate enhancement pattern on CE-MRI. On histopathology, 5 (83.33%) cases showed PLONI and all 6 (100%) had optic nerve head infiltration. The cut end of optic nerve was free in all cases. On correlating MRI and HPE, all eyes with solid enhancement pattern showed PLONI, of which (2/3, 66.6%) had diffuse ON infiltration. Only 50% of eyes with tram track patterns showed PLONI. The case which showed a punctate enhancement pattern showed focal infiltration by tumor cells with vacuolated cytoplasm on HPE. At last follow-up, all patients are alive and free of disease.CONCLUSION:-Optic nerve enhancement patterns may make it more predictive for PLONI on HPE. Solid enhancement pattern appears to correlate better with the extent of ON invasion on HPE and longer lengths of solid optic nerve enhancement may be considered for neoadjuvant chemotherapy rather than upfront enucleation.