Objective: The Chiari I malformation is defined as tonsillar herniation of at least 3 to 5 mm below the foramen magnum. Although Chiari I malformation is considered to derive from a mesodermal disorder resulting in underdevelopment of the posterior fossa relative to its content, evidence for a possible heterogeneous etiology also has been reported. The aim of the present study is to elucidate the relationship between Chiari I malformation and mental retardation, speech delay, and epilepsy to consider a possible specific pathogenetic background.
Methods: Thirty-five patients with Chiari I malformations were identified by use of magnetic resonance imaging during a period between 1993 and 1999. The study consisted of nine patients (four boys and five girls) who were affected by mental retardation, speech delay, and epilepsy. All patients underwent electroencephalography and brain and cervical spine magnetic resonance imaging.
Results: All patients were mentally retarded with a mean intelligence quotient of 50. Seven patients had a positive history for speech delay, and five were epileptic. Electroencephalograms demonstrated abnormalities in seven patients. The mean tonsillar displacement was 10.1 mm. A thin corpus callosum and a wide cavum septum pellucidum were present in three patients. Neither hydromyelia nor scoliosis was observed. No correlation between the degree of the ectopia and clinical manifestation was noted.
Conclusion: The association of Chiari I malformation with epilepsy, speech delay, and mental retardation may not be a mere incidental finding but may be a marker for a different pathogenetic background.