Bone Abstracts

Background: X-linked hypophosphatemic rickets (XLHR) represents the most common form of hypophosphatemia.

Aim: The aim of this prospective study was to describe and analyze the incidence of cranial and cervico-occipital junction (COJ) anomalies in a series of children with XLHR.

Patients and methods: Seventeen children (13 girls, 4 boys, mean age 7.3 years) followed for XLHR at the French national reference center for rare diseases of the calcium and phosphate metabolism were included. All patients consented to the CT scan of the skull and MRI of the COJ. On CT, the patency of the sutures was noted. The cranial index was calculated as biparietal diameter divided by the occipitofrontal diameter and multiplied by 100. On MRI, the position of the cerebellar tonsils was analyzed. A Chiari type 1 malformation was considered when the cerebellar tonsils were lower than 5 mm from the foramen magnum edge on sagittal slices. The volume of the subarachnoid spaces and of the ventricles was also assessed.

Results: All children had a dolichocephalic deformation. In 12/17 children, a full or partial cranial synostosis of the sagittal suture was found. In two children, the right coronal suture was also partially affected with a plagiocephalic deviation of the forehead and of orbital bandeau. In one child, a closure of both lambdoids was associated to the loss of the sagittal suture. In nine children, we found a Chiari 1 malformation. All of them presented also a full or partial fusion of the sagittal suture. No child with an overt patent sagittal suture had a Chiari malformation. Children with Chiari 1 malformation had a smaller cranial index compared to those without (P=0.021).

Conclusions: This study highlights that cranial synostosis and Chiari 1 malformation are more frequent in XLHR than previously thought and related to the impaired growth of the cranial bones. It is still necessary to investigate further the clinical consequences of these findings and the modalities for their radiological follow-up to adjust indications for neurosurgery.

Disclosure: The authors declared no competing interests.