A 64-Year-Old Man Presenting With Diplopia and Right Orbital Swelling Due to Mucosa-Associated Lymphoid Tissue Lymphoma.

BACKGROUND Non-Hodgkin lymphoma (NHL) is the most common primary cancerous tumor of the orbit in adults. Orbital mucosa-associated lymphoid tissue (MALT) lymphoma is a slow-growing, low-grade B-cell NHL that typically presents as painless swelling or diplopia, with a favorable prognosis. These tumors often arise from acquired lymphoid tissue and may be associated with chronic inflammatory or autoimmune conditions. This report describes a 64-year-old man who presented with diplopia and right orbital swelling caused by orbital MALT lymphoma. He was treated with surgical excision followed by radiotherapy. This case highlights the clinical presentation, diagnostic process, and therapeutic response of localized orbital MALT lymphoma. CASE REPORT A 64-year-old man presented with a gradually enlarging right orbital swelling over several years, with increased diplopia over the last year. The patient denied pain, vision loss, or systemic symptoms such as weight loss, fever, or night sweats. Examination found a firm superonasal orbital mass, mild eyelid drooping, and limited upward movement of the eye. Visual acuity and pupillary reactions were preserved. A computed tomography (CT) scan revealed a soft-tissue lesion involving the superior rectus muscle, with no evidence of bony erosion. A biopsy identified low-grade MALT lymphoma based on histopathological and immunohistochemical findings. Systemic staging showed no evidence of metastasis or extraorbital involvement. The patient was treated with surgery and radiotherapy, resulting in a significant decrease in the orbital mass and minimal residual diplopia after 3 months. The patient tolerated the treatment well, and there were no major complications. CONCLUSIONS Orbital MALT lymphoma can develop subtly and may mimic benign orbital conditions, leading to delays in diagnosis. Early detection relies on comprehensive imaging and histopathological evaluation. Localized cancerous disease typically responds well to radiotherapy, as demonstrated in this case. This underscores the importance of prompt diagnosis and treatment to achieve the best outcomes and preserve visual function.