Imaging Features of Pediatric Primary Orbital Lymphomas: A Rare Case With Histopathological Correlation and Systematic Literature Review.

Pediatric primary orbital lymphomas are exceptionally rare entities and represent a very small subset of both childhood orbital tumors and extra-nodal non-Hodgkin lymphomas. They often present with non-specific clinical features that can closely mimic inflammatory or other malignant orbital conditions, thereby posing significant diagnostic challenges. We report a rare case of an orbital lymphoma in an infant presenting with rapidly progressive, painless unilateral eyelid swelling. Magnetic resonance imaging demonstrated a well-defined extraconal orbital mass that appeared isointense on T1-weighted images and iso- to hypointense on T2-weighted sequences, with homogeneous post-contrast enhancement. The lesion exhibited marked diffusion restriction with significantly reduced apparent diffusion coefficient (ADC) values, indicative of a highly cellular neoplasm and in this context, most favorable diagnosis of lymphoma was considered. Histopathological evaluation, supported by immunohistochemistry and flow cytometry, confirmed an aggressive B-cell lymphoma, and molecular analysis revealed features consistent with Burkitt lymphoma. Staging fluorodeoxyglucose positron emission tomography demonstrated residual metabolically active disease confined to the orbit without evidence of systemic involvement. The patient was initiated on intensive multi-agent chemotherapy with an early favorable clinical response. A systematic review of the literature was subsequently done, which highlighted the extreme rarity of primary pediatric orbital lymphomas, with a predominance of high-grade B-cell histology, particularly Burkitt lymphoma. This case highlights the critical role of diffusion-weighted imaging and low ADC values in differentiating orbital lymphomas from other pediatric orbital masses, thereby facilitating early diagnosis, accurate lesion characterization, and timely initiation of therapy. Radiological awareness of these characteristic imaging features is essential to avoid diagnostic delay and to improve clinical outcomes in this rare but aggressive disease, given its marked responsiveness to treatment.