Metastatic unilateral retinoblastoma to the contralateral orbital optic nerve presenting with optic disc edema

Retinoblastoma (Rb) is a malignant eye tumor that poses a significant risk of mortality once metastasized. We present the case of a 30-month-old girl with left-sided Rb who underwent primary enucleation with pathology-confirmed diagnosis without high-risk pathologic features. Therefore she did not receive adjuvant chemotherapy. Six months later, the patient developed skull bone and bone marrow metastasis, which were treated with systemic chemotherapy, excision of bone metastasis, focal radiation treatment to the site of osseous metastasis, and bone marrow transplantation. Follow-up for two years was unremarkable until she presented with vision loss in the remaining contralateral eye. Ophthalmic examination revealed severe optic disc edema without intraocular masses, initially thought to be optic neuritis. However, the patient did not respond to steroids, and the initial cerebrospinal fluid (CSF) analysis was negative. This was repeated based on high clinical suspicion of metastasis, revealing only a few malignant cells. The presentation and appearance of the optic nerve were considered metastasis-related and treated with radiation therapy, which resulted in dramatic clinical and radiological improvement. Unfortunately, a few weeks later, the patient developed lower limb weakness, and imaging showed diffuse leptomeningeal metastasis, confirmed by CSF findings. This case represents the first documented isolated contralateral optic nerve metastasis in Rb.