EC Paediatrics

T-cell acute lymphoblastic leukemia (T-ALL) is a malignant hematologic disorder that may be complicated by extramedullary involvement, particularly within the central nervous system. Leukemic infiltration of the optic nerve is rare and usually occurs in association with orbital, meningeal, or vascular involvement. Isolated bilateral optic nerve infiltration remains exceptional and represents a diagnostic pitfall, particularly when presenting with clinical features mimicking inflammatory optic neuritis. We report the case of a 5-year-old child with T-ALL in complete remission for five months after chemotherapy, admitted for progressive bilateral blindness associated with headaches. Ophthalmologic examination was strictly normal. Complete blood count revealed hyperleukocytosis associated with bicytopenia. Brain computed tomography demonstrated bilateral optic nerve thickening without associated cerebral parenchymal abnormalities. Orbito-cerebral MRI revealed diffuse and marked thickening of both optic nerves along their entire course, appearing isointense on T2-weighted images, hypointense on STIR sequences, with intense and homogeneous enhancement after gadolinium administration. No intraconal fat infiltration or chiasmatic involvement was observed. Diffusion-weighted imaging was not contributive. Cerebrospinal fluid analysis and bone marrow aspiration confirmed leukemic relapse by demonstrating blast cells. Leukemic optic nerve involvement represents a rare extramedullary localization and may constitute a diagnostic challenge for radiologists. MRI plays a pivotal role in differentiating tumor infiltration from other causes of optic nerve involvement. Any optic nerve involvement in a pediatric patient with acute lymphoblastic leukemia, even during apparent remission, should raise suspicion for leukemic relapse. Prompt multidisciplinary management is essential to preserve visual function and overall prognosis.

 Keywords: Optic Nerve Leukemic Infiltration; Acute Lymphoblastic Leukemia; Bilateral Blindness; Orbito-Cerebral MRI; Orbital Radiotherapy

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