Unusual presentation of a retrobulbar optic nerve sheath meningioma: a case report.

Introduction: We report a case of a slowly progressive unilateral visual field defect associated with an atypical retrobulbar optic nerve sheath lesion in the context of concurrent breast cancer, which was ultimately diagnosed as meningothelial meningioma. Case description: A 50-year-old woman presented with a 2-year history of painless, progressive visual impairment and a perceived altitudinal visual field defect in the left eye, with MRI revealing a retrobulbar T2-weighted hyperintense lesion of unclear nature in the setting of a recent diagnosis of breast carcinoma. Neuro-ophthalmic evaluation showed superonasal parapapillary retinoschisis, inferotemporal ganglion cell loss on OCT, and absolute superior scotoma on static perimetry, with preserved central visual acuity. To exclude metastatic disease and confirm the suspected diagnosis, an optic nerve sheath biopsy was performed, revealing WHO grade I meningothelial meningioma. Postoperatively, the visual field defect initially appeared enlarged. At the 1-week follow-up, there was reduced visual acuity and OCT findings consistent with a microvascular ischemic event, whereas the visual field defect returned to its preoperative pattern. Conclusion: This case highlights the diagnostic challenges of atypical retrobulbar optic nerve sheath lesions in the context of concurrent malignancy and underscores the feasibility and value of tissue diagnosis in selected patients to guide management.