The prevalence and characteristics of ocular adnexal lymphomas of the conjunctiva and orbit

Purpose: Ocular adnexal lymphoma (OAL) most commonly affects the orbit and conjunctiva. There exist numerous subtypes of lymphoma that carry different risks and prognoses. When it affects the conjunctive, the most common site of adnexal lymphoma, it typically presents as a unilateral, slightly elevated, well-circumscribed salmon-patch lesion. Usually, there are no systemic manifestations other than the extranodal site. When it affects the orbit, it can present with proptosis, ptosis, and decreased extraocular movements. On histopathology, both will appear as a diffuse or nodular proliferation of small lymphocytes with mild-to-moderate atypia, few mitotic figures, and numerous Dutcher and Russell bodies. An immunohistochemical (IHC) panel is essential to differentiate the subtype of lymphomas from each other and their benign counterpart, lymphoid hyperplasia (LH). The aim of the study is to determine the frequency and characteristics of OAL of the orbit and conjunctiva. Methods: Fifty-eight patients with lymphoid tumors between 2006 and 2024 were studied at the McGill Ocular Pathology and Translational Research Laboratory. Statistical analysis of the data was done using GraphPad Prism. Results: Fifty-eight patients were included in this study, among which 32 lymphomas and 26 LHs. Among the lymphomas, the conjunctiva and orbit were by far the most common sites with 40.6% and 43.8% of cases affecting each respective location. Analysis of the IHC data was done in the orbital and conjunctival lymphoma cases, n = 27. Ki-67 expression was statistically higher in high-grade lymphomas than their low-grade counterparts ( P = 0.0182). Although lymphoma cases were both mono- and polyclonal, LH was found to be only polyclonal (100%, n = 18 / 18). Conclusions: OAL most commonly affects the conjunctiva and orbit, and is most commonly of B-cell lineage. An IHC panel and expert pathologist analysis are necessary to make the final diagnosis of the lymphoma subtype. Meanwhile, LH is predominantly polyclonal, with both B- and T-cell lineage. The differential diagnosis is clinicopathological but relies on immunohistochemistry to identify malignant lymphoid tumors.