ESPE Abstracts

Introduction: X-linked hypophosphatemic rickets (XLHR) represents the most common form of genetic hypophosphatemia and causes rickets in children because of increased FGF23 secretion and renal phosphate wasting. Even though cranial vault an craniovertebral anomalies of potential neurosurgical interest, namely early closure of the cranial sutures and Chiari type I malformation (CM-I), have been observed in children with XLH, their actual incidence and characteristics are not established.

Aim: The main aim of this study was to analyse the prevalence of cranial and CM-I in children with XLH and to identify the predictive factors of these anomalies. The secondary aim of this study was to verify the usefulness of MRI specific scans as an alternative tool to CT for the diagnosis of these anomalies.

Material and methods: We prospectively performed Neuroradiological evaluation in nine of the eleven XLH children followed at our Pediatric Clinic: 9 Children (five females and four males, mean age 8,5 ± 5 years at the radiological evaluation, all were on burosumab treatment since mean age of 5,8 ± 4,2 years) underwent CT scans of head and skull; moreover three children also underwent MRI “black bone” sequences and two children underwent MR-Angiography (MRA). We found that 44% of XLH children had a complete or partial fusion of the sagittal suture and 33% of XLH children showed protrusion of the cerebellar tonsils. The male sex was associated with craniosynostosis (P<0.01), and craniosynostosis was associated with abnormal descent of cerebellar tonsils (P<0.01). All the patients with radiological diagnosis of CM-I showed symptoms (headache). Three patients with no craniosynostosis underwent MRI with black bone sequences to evaluate the visibility of the sutures: all the cranial sutures were consistently identified on "Black Bone" MRI. One patient with cranial synostosis and CM-I, diagnosed on skull CT, underwent MRA, showing absence of flow in the transverse venous sinuses.

Conclusions: This study highlights that sagittal suture fusion and CM-I is a frequent complications of XLH. Male sex was a strong predictor of craniosynostosis. All patients were on burosumab and the impact of a very precious start of this treatment on this complication has to be clarified. Because diagnosis of craniovertebral anomalies can be underestimated on a purely clinical basis, radiological studies should be considered in XLHR children. This study highlights that MRI with Black bone sequences are demonstrating considerable clinical potential as a non-ionizing alternative to CT in the diagnosis of craniosynostosis.