The Chiari malformation is an infrequently detected congenital anomaly characterized by the downward displacement of the cerebellum with a tonsillar herniation below the foramen magnum that may be accompanied by either syringomyelia or hydrocephalus. Surgery, such as foramen magnum decompression, is indicated for a symptomatic Chiari malformation, although an incidental lesion may be followed-up without further treatment. Infrequently, increased intracranial pressure emerges due to hyperthyroidism. A nineteen-year-old girl visited our outpatient clinic presented with a headache, nausea and vomiting. A brain and spinal magnetic resonance image study (MRI) indicated that the patient had a Chiari I malformation without syringomyelia or hydrocephalus. An enlarged thyroid gland was detected on a physical examination, and serum markers indicated Graves' disease. The patient started anti-hyperthyroid medical treatment. Subsequently, the headache disappeared after the medical treatment of hyperthyroidism without surgical intervention for the Chiari malformation. A symptomatic Chiari malformation is indicated for surgery, but a surgeon should investigate other potential causes of the symptoms of the Chiari malformation to avoid unnecessary surgery.
Keywords: Chiari malformation; Headach; Hyperthyroidism; Intracranial hypertension.