Intravascular large B-cell lymphoma mimicking an orbital mass lesion and bilateral cavernous sinus syndrome: A case report.

Intravascular large B-cell lymphoma (IVLBCL) is a rare entity that can present with atypical extranodal manifestations, often mimicking other orbital or neurological conditions. A 69-year-old woman presented with rapidly progressive left ptosis and diplopia, which progressed to complete bilateral ophthalmoplegia within several weeks. Magnetic resonance imaging revealed a previously unreported right orbital mass accompanied by bilateral cavernous sinus (CS) enhancement, representing a novel imaging feature of IVLBCL. The diagnosis was established by sphenoid sinus biopsy. The patient achieved near-clinical remission, with almost complete resolution of the orbital mass, following rituximab, cyclophosphamide, doxorubicin, vincristine and prednisolone (R-CHOP) chemotherapy combined with a Bruton tyrosine kinase inhibitor and intravenous high-dose methotrexate. However, diplopia recurred at 3 months post-treatment, indicating that although the patient initially responded well to R-CHOP-based combination therapy, more effective maintenance or consolidation strategies should be actively explored for patients with IVLBCL involving the central nervous system. Clinically, various lymphoma subtypes should be considered in the differential diagnosis of patients presenting with CS and intraorbital lesions.