A rare case of orbital mantle cell lymphoma presenting as a well-demarcated mass on magnetic resonance imaging.

A 71-year-old male presented with painless and slowly progressive proptosis of the right eye. The patient had no history of cancer and was in good health. Orbital magnetic resonance imaging showed a well-demarcated, slightly lobulated intraconal orbital mass hypo-isointense on T1- weighted and isointense on T2-weighted images, demonstrating contrast enhancement in the right orbit. The lesion had a central cavitary region. An anterior orbitotomy with lower lid crease incision was performed and the lesion was excised in toto. Histopathologic examination revealed diffuse infiltration of monomorphic population of small lymphoid cells. Immunohistochemical staining demonstrated diffuse and strong positivity for CD20, CD5, and cyclin D1. Histopathological and immunohistochemical findings were consistent with mantle cell lymphoma. Positron emission tomography-computed tomography did not show systemic involvement. The patient underwent orbital external beam radiotherapy (36 Gy). There was no recurrence and/or systemic involvement at 2.5 years follow-up.