Sagittal suture fusion and Chiari type 1 malformation are commonly observed complications of X-linked hypophosphatemic rickets (XLHR), and because the presence of craniovertebral anomalies can be underestimated, radiologic imaging should be considered in this population to ensure an accurate diagnosis, according to study findings published in the Journal of Bone and Mineral Research.
XLHR is the most common type of genetic hypophosphatemia and causes rickets and osteomalacia in children due to elevated secretion of fibroblast growth factor 23 and renal phosphate wasting. While cranial vault and craniovertebral anomalies have been observed in children with XLHR, the incidence and characteristics have not been well defined. In this study, researchers examined the incidence of cranial and cervico-occipital junction anomalies in 44 children with XLHR who underwent computed tomography (CT) scans of the head and skull and were followed at the Reference Centre for Rare Diseases of the Calcium and Phosphate Metabolism in Paris, France.
Craniosynostosis was identified in 26 children with XLHR (59%) and involved the sagittal suture in all cases, which was completely fused in 18 patients and partially fused in 8. A cranial index <75% was observed in 16 patients (36%) and mesocephaly in 18 patients (41%), while the remaining 10 patients (23%) had a normal cranial index >80%. In assessing for Chiari type 1 malformation, 5 patients were unable to undergo radiologic interpretation. A quarter of the cohort had protrusion of the cerebellar tonsils (descent <5 mm), and a history of dental abscesses was linked with craniosynostosis, which was associated with abnormal descent of cerebellar tonsils.
“This study highlights that sagittal suture fusion, ie, craniosynostosis and Chiari 1 malformation, are  common complications that are associated with the severity of disease in children with XLHR,” concluded the researchers, adding that their results demonstrate that a “radiological evaluation should be considered in [children with XLHR] if a proper diagnosis is warranted because cranial vault and craniovertebral anomalies are underestimated by clinical evaluation only.”
Rothenbuhler A, Fadel N, Debza Y, et al. High incidence of cranial synostosis and Chiari I malformation in children with x-linked hypophosphatemic rickets (XLHR). J Bone Miner Res. 2018;33:1-7.