Development of Progressive Chiari I Malformation in a Child with Unilateral Sporadic Retinoblastoma

PURPOSE: To report a case of progressive Chiari malformation type I (CIM) in a patient with unilateral sporadic retinoblastoma (RB) treated with intra-arterial chemotherapy (IAC) and enucleation. METHODS: A 5-year-old male patient with a history of RB in his left eye treated with IAC and enucleation presented to our clinic for routine RB surveillance. Radiotherapy had not been used for the treatment of his RB. RESULTS: A progressive herniation of cerebellar tonsils through the foramen magnum was detected on follow-up magnetic resonance imaging (MRI). Brain and cervical MRI revealed no central nervous system mass, hydrocephalus, or syringomyelia. There was no history of head trauma. CONCLUSION: Progressive CIM may occur in unilateral sporadic RB.