En-bloc posterior vault distraction including the foramen magnum for Chiari I malformation in severe syndromic craniosynostosis: First cases and literature review.

This case series describes two patients with severe Crouzon syndrome and persistent Chiari I malformation. Initial treatment with standard posterior vault distraction osteogenesis and frontoorbital advancement failed to resolve the patient's symptoms. One patient developed severe syringomyelia and myelopathy refractory even to standard suboccipital decompression. Given the persistent posterior fossa constriction, an en-bloc posterior vault distraction incorporating the foramen magnum was performed over 21 days, achieving an expansion of 20 mm. This approach resulted in complete symptom resolution in both patients, disappearance of syringomyelia, and normalization of posterior fossa anatomy. One procedure was guided by intraoperative cone-beam CT (Brainlab Loop-X) to optimize the distraction vector and ensure optimal ventricular catheter placement during the concomitant shunt revision. These are the first reported cases of en-bloc posterior vault distractions incorporating the foramen magnum to simultaneously address both posterior cranial restriction and secondary Chiari I malformation. They proof the feasibility of a mono-bloc technique to simultaneously distract the posterior cranial vault and the posterior fossa down to the foramen magnum.