Optic Perineuritis Mimicking Optic Nerve Sheath Meningioma: A Case Series

Introduction: Optic perineuritis (OPN) can mimic optic nerve sheath meningioma (ONSM) both clinically and radiographically, which may lead to misdiagnosis and inappropriate treatment. Case Presentations: We describe two cases of autoimmune-related OPN that were initially presumed to be ONSM. The first case involves a 61-year-old African American woman with longstanding vision loss and optic nerve sheath enhancement thought to be sarcoidosis due to its steroid responsiveness and subsequent resolution of radiographic findings. The second case involves a 51-year-old woman with a history of triple-negative breast cancer presenting with monocular vision loss that underwent radiotherapy for presumed ONSM, without any visual improvement. She was later diagnosed with chronic relapsing inflammatory optic neuropathy (CRION) due to absence of malignancy on imaging, unremarkable workup, and steroid-dependent, relapsing course. Conclusion: In both patients, the tram-track sign was seen on MRI, complicating the diagnostic process. These cases emphasize the importance of recognizing inflammatory optic neuropathies that can masquerade as neoplastic processes. Sarcoidosis is known to mimic ONSM, however there are currently no reports of CRION mimicking ONSM to our review. Given the therapeutic implications, including the potential for unnecessary radiation as in the second presented case, a thorough diagnostic workup is essential prior to initiating definitive treatment.