2026 年 13 巻 p. 167-174
Chiari malformation type I is a structural anomaly of the posterior fossa characterized by cerebellar tonsillar herniation through the foramen magnum, often associated with disrupted cerebrospinal fluid dynamics and elevated intracranial pressure. Papilledema is a rare ophthalmic manifestation in Chiari malformation type I, typically linked to increased intracranial pressure. Isolated visual symptoms without signs of intracranial pressure in pediatric Chiari malformation type I are particularly rare and poorly understood. We report a rare pediatric case of Chiari malformation type I in a 9-year-old girl presenting solely with bilateral papilledema and visual impairment, without typical symptoms of raised intracranial pressure such as headache. Magnetic resonance imaging revealed cerebellar tonsillar descent and cervical syringomyelia. Due to progressive visual decline and the absence of alternative diagnoses, the patient underwent foramen magnum decompression with C1 laminectomy. Postoperatively, visual acuity significantly improved, although papilledema persisted at 9 months. This case challenges the conventional view that papilledema in Chiari malformation type I is solely caused by elevated intracranial pressure. Alternative mechanisms, such as localized venous congestion, mechanical stress on the optic nerve, or regional cerebrospinal fluid flow disturbances, may contribute to papilledema. Persistent papilledema despite clinical improvement supports the hypothesis of localized rather than global intracranial pressure elevation. Pediatric presentations may differ from adult cases in symptomatology and pathophysiology, requiring careful diagnostic and therapeutic considerations. Surgical decompression may lead to functional visual recovery even if anatomical signs such as papilledema persist. This case underscores the need for further research into atypical presentations and underlying mechanisms of Chiari malformation type I, especially in pediatric populations.
