A Rare Incidentally Discovered Solitary Extramedullary Plasmacytoma of The Orbit and Meninges

Introduction: Orbital plasmacytomas are rare hematologic malignancies, accounting for less than 1% of all orbital tumors. Approximately 50-65% of patients with orbital plasmacytomas have known multiple myeloma (MM) at the time of diagnosis, and of those without known systemic disease, further workup identifies occult MM in 20-37% of patients. Solitary orbital plasmacytomas represent an exceedingly rare subtype not associated with systemic myeloma, and of those reported in the literature, patients presented with visual complaints including unilateral proptosis, a palpable lump, diplopia, blurred vision, orbital pain, ptosis, and eye redness. The authors present a case of an impressive asymptomatic solitary orbital and meningeal plasmacytoma identified on routine neuroimaging following head trauma. Methods: This is a case report. The patient's medical record, imaging studies and pathology findings were reviewed. Results: A 71-year-old male presented to the emergency room after a fall while intoxicated. Head CT scan, and further clarifying Magnetic Resonance Imaging (MRI), demonstrated unilateral left extraocular muscles, optic nerve, perineural, and pachymeningeal enhancement with radiographic orbital apex congestion ([ Fig. 1 ]). He denied any visual complaints such as diplopia, orbital pain, or blurry vision. Vision was 20/25 in both eyes with full motility and no pupil defects. 3mm of incidental relative left proptosis was measured on exophthalmometry, however no other orbital signs were present and comprehensive dilated ophthalmic exam was otherwise normal ([ Fig. 2 ]). Complete inflammatory and infectious workup was normal. Oncologic workup identified a monoclonal IgG kappa gammopathy on serology and CSF analysis. Meningeal biopsy was pursued to reduce potential visual morbidity associated with a deep orbit biopsy in an otherwise asymptomatic eye. Meningeal tissue demonstrated a lesion rich in plasma cells on hematoxylin and eosin ([ Fig. 3 ], panel A) staining positive for CD38 ([ Fig. 3 ], panel B) and CD138 and with kappa clonality on in-situ hybridization ([ Fig. 3 ], panel C+D), confirming a final diagnosis of plasmacytoma. Bone marrow biopsy showed no evidence of plasma cell neoplasm. PET/CT showed no evidence of metabolic active malignancy except known left orbital/cavernous sinus extramedullary plasmacytoma. The patient received 45 Gy of fractionated radiation with significant radiographic response of the lesion at six month following treatment ([ Fig. 4 ]). He maintained excellent 20/25 visual acuity, full motility with no diplopia, and no evidence of optic neuropathy despite his initial impressive radiographic orbital apex congestion and remained free of multiple myeloma on close systemic surveillance one year post treatment. Conclusion: Solitary orbital plasmacytomas may mimic a wide differential including orbital inflammatory syndrome, thyroid eyes disease, or metastatic disease on imaging. In this case, comprehensive serologic workup, thoughtful tissue biopsy to reduce risk of visual morbidity, and complete oncologic evaluation for underlying multiple myeloma was crucial in both diagnosis and treatment of this unusual orbital process. The case represents an extremely rare asymptomatic presentation of an impressive solitary orbital plasmacytoma whose prompt multi-disciplinary treatment preserved vision and highlights the importance of systemic monitoring for multiple myeloma. Fig. 1 Fig. 2 Fig. 3 Fig. 4 Publication History Article published online: 27 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany