Abstract
PURPOSE: To report a 65-year-old male patient with primary lateral rectus large B cell lymphoma. OBSERVATIONS: The patient had been referred because of progressive proptosis and limitation of ductions, especially abduction (ortho position at primary gaze) and conjunctival injection. Computerized tomography of the orbit and paranasal sinuses depicted a massive lateral rectus muscle enlargement without any other orbital involvement. Lateral orbitotomy and lateral rectus belly incisional biopsy was done, and histopathologic and immunohistochemical staining and systemic evaluations revealed the diagnosis of primary orbital large B-cell lymphoma. CONCLUSIONS AND IMPORTANCE: This case indicated that, though rare, extraocular muscle enlargement could be the main finding of primary orbital lymphoma. Large B-cell lymphoma could involve only the orbital tissues, although it is more prevalent with systemic involvement.