Orbital lymphoma presenting as preseptal cellulitis in a child with ataxia-telangiectasia.

Ataxia-telangiectasia (AT) is a rare autosomal recessive disorder associated with immunodeficiency and an increased risk of malignancy. We report a young child with AT and severe combined immunodeficiency who initially presented with left periorbital swelling and was treated for a presumed periorbital infection. She later presented with fever and was diagnosed with pneumonia, requiring admission. Despite antimicrobial therapy and surgical drainage, the swelling persisted and progressed rapidly.MRI of the brain and orbits demonstrated complicated sinusitis with a medial extraconal lesion, suggesting an infectious process. However, there was no sustained clinical response, and microbiological studies remained negative. Repeat MRI showed a persistent lesion with extension into adjacent structures. Histopathological examination confirmed non-Hodgkin B-cell lymphoma with a high proliferative index (Ki-67~80%).This case highlights the importance of early reassessment in immunocompromised patients with an atypical clinical course.