Chiari I malformation: association with hypophosphatemic rickets and MR imaging appearance.

Abstract

To evaluate for an association between familial hypophosphatemic rickets (FHR) and Chiari I malformation (CM1). Sixteen patients with FHR underwent magnetic resonance (MR) imaging of the cervicomedullary junction. Images were analyzed by three radiologists for cerebellar tonsillar ectopia, syringohydromyelia, calvarial bone thickening, a flat posterior fossa, and cervical spinal stenosis. Final diagnoses were made by means of consensus. Tonsillar ectopia of 4 mm indicated CM1. Subjects underwent neurologic examination and completed a questionnaire. Medical records were retrospectively reviewed. A two-sided Fisher exact test was used to test for independence between CM1 and bone thickening or ventriculomegaly. Seven subjects (44%) had CM1. The more severe the bone thickening, the more likely that a CM1 was present. Four subjects (25%) had cervical spinal stenosis. Findings indicate that CM1 is associated with FHR and that the primary abnormality in patients with CM1 is a small posterior fossa caused by a bony malformation.