A prospective natural history study of nonoperatively managed Chiari I malformation: does follow-up MRI surveillance alter surgical decision making?

OBJECT Chiari malformation Type I (CM-I) in children is a common incidental finding. Resolution of cerebellar tonsil ectopia has been reported, but no studies have followed tonsil position over regular intervals throughout childhood. To better elucidate the clinical and radiological natural history of CM-I in children, the authors prospectively followed up children with nonoperatively managed CM-I for up to 7 years. METHODS The study included all children evaluated for CM-I over a period of 12 years for whom surgery was not initially recommended. The study excluded patients with associated conditions, including syringomyelia and hydrocephalus. For all patients, initial management was nonoperative, and follow-up management consisted of annual cervical spine or brain MRI and clinical examination. At each follow-up examination, the neurological examination findings, subjective symptoms, and the position of the cerebellar tonsils on MR images were recorded. An alteration in tonsillar descent of 2 mm or greater was considered a change. RESULTS Neurological examination findings did not change over the course of the study in the 52 children who met the inclusion criteria. Although radiological changes were common, no surgeries were performed solely because of radiological change. Overall, tonsil position on radiological images remained stable in 50% of patients, was reduced in 38%, and increased in 12%. Resolution was seen in 12% of patients. Radiological changes in tonsil position were seen during every year of follow-up. On average, in any given year, 24% of images showed some form of change in tonsil position. A total of 3 patients, for whom no changes were seen on MR images, ultimately underwent surgery for subjective clinical reasons. CONCLUSIONS CM-I in children is not a radiologically static entity but rather is a dynamic one. Radiological changes were seen throughout the 7 years of follow-up. A reduction in tonsillar descent was substantially more common than an increase. Radiological changes did not correlate with neurological examination finding changes, symptom development, or the need for future surgery. Follow-up imaging of asymptomatic children with CM-I did not alter treatment for any patient. It would be reasonable to follow these children with clinical examinations but without regular surveillance MRI.