Bilateral Optic Disk Swelling and Peripheral Visual Field Defects as a Rare Initial Presentation of Primary Chiari I Malformation.

Chiari malformation 1 (CM1) is defined as a herniation of encephalon matter through the base of the skull. The amount of herniation is cited as greater than 3 mm or 5 mm, depending on the source of literature. We report a rare case of a 55-year-old male initially presenting with bilateral papilledema and monocular right lower quadrantanopia, found to have CM1. An MRI confirmed 4.87 mm herniation of the cerebellar tonsils at the foramen magnum, and he was diagnosed with CM1. He was later found to have a normal opening pressure on lumbar puncture at 10 cm H2O. This poses an interesting clinical question as papilledema is defined by elevated intracranial pressure. The ophthalmic defects of this patient with normal intracranial pressure and CM1 are explored in this report.