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

PURPOSE: To evaluate for an association between familial hypophosphatemic rickets (FHR) and Chiari I malformation (CM1).

MATERIALS AND

METHODS

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.

RESULTS

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.

CONCLUSION

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.