ESPE Abstracts

Background: X-linked hypophosphatemic rickets (XLHR) represents the most common form of genetic hypophosphatemia. Even though skull and cranio-vertebral anomalies of potential neurosurgical interest are observed in children with XLHR, their actual incidence and characteristics are not well established. We aimed to analyze the incidence of Chiari type I anomalies in children with XLHR

Methods and materials: Our retrospective monocentric study in XLHR patients followed at the French National Reference Center for Rare Diseases of the Calcium and Phosphate Metabolism analysescranial and spinal CT and MRI

Results: Fifty-six children(35 girls) with XLHR were included. Age at initial MRI was 9.1 ± 3.8 years (range 3 to 19 years). On sagittal reconstructions, a clear descent of cerebellar tonsils was identified in 32 (57%) of the patients. Among them, 16 patients presented with low-lying tonsils (benign tonsillar ectopia < 5mm) and 16 patients with Chiari I (> 5 mm). Among Chiari I patients, 9 patients (56%) also presented a brainstem descent. Syringomyelia was detected in four patients with a Chiari I > 5 mm. Four - out of 16 (25%) patients with a Chiari I malformation required neurosurgery, three of which also had syringomyelia. Previous brain/skull CT scans were available in 32 patients. CT scan was interpreted as normal in three patients who had a Chiari I and in six patients who had low-lying tonsils on MRI. Follow-up MRIs were available in 39 patients (interval between two MRI 3-8 years). Among the 30 patients who had a normal initial MRI, one patient showed a Chiari I anomaly six years after initial evaluation (not necessitating surgery). The nine patients diagnosed with a Chiari I initially showed no progression on follow-up MRI and none of the patients had neurosurgery.

Conclusion: Our study of 56 young XLHR patients confirms the high incidence of protrusion of the cerebellar tonsils and Chiari I anomalies in this rare disease. In this study based on MRIs the incidence of Chiari I is higher than that observed in our previous study on CT scans, 28.5% vs 16%. Follow-up MRI were reassuring, no progression of Chiari I anomaly was noted and only one patient developed Chiari I anomaly during follow-up.