[Spontaneous syncope as the only sign of Arnold-Chiari type I malformations].

We present a patient suffering from spontaneous recurrent syncopes as the sole symptom of Arnold-Chiari type I malformation. The syncopes were attributed to transient compression of neural and/or vascular structures at the cranio-cervical junction by the descended cerebellar tonsils, triggered by an increase in intracranial pressure. The disappearance of symptoms after posterior fossa decompression confirmed our hypothesis.