Chiari 1 malformation and holocord syringomyelia in hunter syndrome.

Compressive cervical myelopathy is a well-known life-threatening complication in mucopolysaccharidosis (MPS) patients. Glycosaminoglycan accumulation in the growing cartilage results in dens dysplasia, atlanto-axial instability, and subsequent periodontoid fibrocartilaginous tissue deposition with upper cervical stenosis.Chiari malformation type 1 (CM1) is a congenital downward cerebellar tonsil ectopia determined by clivus and posterior cranial fossa underdevelopment, possibly leading to progressive spinal cord cavitation (syringomyelia) and severe neurological impairment.We present a boy affected with Hunter syndrome (MPS II) and cerebellar tonsil ectopia who developed a holocord syringomyelia at the age of 6 years. The child underwent atlanto-occipital decompressive surgery with rapid clinical and neuroimaging improvement.Sharing a primary mesenchymal involvement of the cervical-occipital region, the coexistence of CM1 in MPS might be not unexpected and complicate further the disease course. In these patients, strict monitoring and prompt treatment might be of foremost importance for preventing major neurological complications.