Supplementary Material for: Histopathological Analysis of an Acquired Vitreous Cyst with Pigmented Epiretinal Membrane Following Vitrectomy: A Case Report

Introduction: In this study, we report a case of an acquired fixed vitreous cyst associated with a pigmented epiretinal membrane (ERM) that developed approximately 10 years after vitrectomy for vitreous hemorrhage (VH) secondary to branch retinal vein occlusion (BRVO). Case Presentation: In this study involved an 85-year-old male who had previously undergone a vitrectomy in November 2014 for a VH caused by BRVO. The patient's postoperative recovery was favorable, however, at a follow-up visit in January 2023 a pigmented ERM was observed, along with an adjacent cyst approximately one-third optic-disc diameter. Initially, the lesion presented as cystoid macular edema (CME) with multiple cystoid spaces, one of which that had gradually enlarged and eventually formed into a pigmented vitreous cyst of approximately two optic-disc diameters in size by January 2025. The cyst was surgically excised, and histological analysis revealed that the cyst wall demonstrated a bilayered structure; i.e., the outer layer consisting of retinal pigment epithelial (RPE), while the inner layer being composed of glial lineage cells. Conclusion: Based on our findings, we hypothesize that the wall of a cystoid space in CME formed a protrusion from the retina into the vitreous cavity, which subsequently developed into a vitreous cyst through migration and proliferation of reactive Müller cells and RPE cells due to structural compromise of the retina.