Cyst-like recurrence of retinoblastoma diagnosed by multimodal imaging

Purpose: To illustrate the diagnosis and management of an atypical, cyst-like recurrence of retinoblastoma. Observations: A 4-month-old boy was diagnosed with Group B retinoblastoma in the right eye, consisting of a 10 x 9 × 3.6 mm retinal tumor temporal to the macula. He was treated with one session of intra-arterial ophthalmic artery chemotherapy using melphalan, followed by three sessions of diode laser transpupillary thermotherapy (TTT), after which complete tumor regression was achieved. 45 weeks after initial treatment, a cystic lesion was detected adjacent to superior margin of the regressed tumor scar. The differential diagnosis included pigment epithelial detachment, retinal gliosis, secondary retinoschisis, and local tumor recurrence. Multimodal imaging including OCT angiography confirmed the diagnosis of local recurrence manifesting as a vascularized cyst-like lesion. Two additional sessions of TTT achieved sustained tumor regression through 16 months of additional follow-up. Conclusions and Importance: Recurrence of retinoblastoma following chemotherapy typically manifests as enlargement of a previously regressed tumor, or seeding into the vitreous or subretinal space. An unusual cyst-like recurrence of retinoblastoma at the margin of a previously regressed tumor was diagnosed by multimodal imaging. Focal diode laser transpupillary thermotherapy was curative.