Acute Lymphoblastic Leukemia (ALL) is the most common childhood malignancy. Despite advancements in therapy, approximately 20% of children with ALL experience a relapse. Isolated optic nerve (ON) relapse is rare in ALL. A delay in initiating treatment can damage the vascular supply to the ON or cause pressure necrosis of the nerve, leading to irreversible vision loss. We describe an emergency of ON compartment syndrome as a relapse of Ph-positive ALL.

An 11-year-old boy, previously treated for Ph-positive ALL with the IC BFM 2009 protocol and imatinib, was admitted 3 months after completing his therapy. He presented with acute holocranial headache, right-sided periorbital pain, and photophobia. A fundoscopy revealed edema of the right optic disc. MRI with contrast showed diffuse thickening of the right optic nerve extending to the chiasm, associated with signs of diffusion restriction, with extension to the cisternal portion of the left optic nerve. After the MRI, CSF was collected, revealing the presence of 541 cells, 0 red blood cells, and 95% B lymphoid lineage blasts by immunophenotyping through flow cytometry (FC). Manometry was performed with an entry pressure of 76 mmHg. No minimal residual disease by FC or BCR gene mutation was found in the bone marrow (BM), and the testis normal. Immediately, the patient received high-dose dexamethasone, dasatinib, intrathecal and systemic chemotherapy, and should receive a hematopoietic stem cell transplant after achieving CSF remission and resolution of optic nerve involvement.

The eye is considered a pharmacologic sanctuary, and ON infiltration represents an ophthalmic emergency requiring urgent intervention. The presentation of optic nerve involvement in leukemia is a visual emergency and may signal an isolated central nervous system relapse, even in the absence of abnormal CSF cytology. This case underscores the importance of recognizing optic nerve infiltration and promptly initiating treatment.