Ocular adnexal lymphomas: A comprehensive review with emphasis on histopathologic and magnetic resonance imaging appearance.

Ocular adnexal lymphomas (OALs) are a heterogeneous group of malignant lymphoproliferative tumors originating from clonal proliferations of lymphocytes, with a multifactorial etiopathogenesis. They can be distinguished in primary, involving ocular adnexa, and secondary, affecting also an additional site. Pathologically OALs encompass four histological subtypes with different biological behaviour and prognosis. The diagnosis relies on clinical manifestations, imaging and histopathological examinations. Clinical symptoms are classified in ophthalmologic, often nonspecific, and constitutional, indicating a systemic involvement. As regards cross-sectional imaging, computed tomography (CT) and magnetic resonance imaging (MRI) play a complementary role, nevertheless MRI outperforms other imaging methods due to the possibility to perform functional techniques such as diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI). At conventional MRI, OALs demonstrate iso- or hypointensity on T1-weighted and T2-weighted sequences relative to cerebral cortex; enhancement is usually homogeneous. PWI and particularly DWI can be useful in discriminating OALs from benign orbital lymphoproliferative disorders (OLPDs) and from other malignant intraorbital tumors, since OALs, due to their high cellularity, demonstrate diffusion restriction with considerably low apparent diffusion coefficient value. Biopsy is needed for final diagnosis and accurate subtyping and grading. Differential diagnosis of OALs, in addition to benign OLPDs, includes granulomatous diseases, metabolic diseases, epithelial neoplasms and metastases. Structured report can be useful to make reporting of imaging findings more accurate and to improve communication between ophthalmologist and radiologist; moreover, it can represent a valuable decision‑supporting tool to assist the multidisciplinary management of the disease. Treatment options include systemic chemotherapy, radiotherapy, immunotherapy and surgical excision.