ABSTRACT
The hallmark of the Chiari I malformation is herniation of the cerebellar tonsils below the level of the foramen magnum. Slight tonsillar ectopia is common, but descent greater than 5 mm is considered signicant. Symptoms associated with this anomaly are related to spinal cord and/or cerebellar compromise and alteration of cerebrospinal uid dynamics, and usually become manifest in early adulthood. However, cough headache may be the only symptom. Despite caudal elongation of the tonsils, the fourth ventricle remains in its normal position. Associated anomalies include Klippel-Feil syndrome (block vertebrae).
