Inferiorly-Directed Posterior Cranial Vault Distraction for Treatment of Chiari Malformations

Purpose

Chiari I malformations involve a small posterior fossa and subsequent herniation of the hindbrain, causing altered cerebrospinal fluid flow and intracranial hypertension (Figure 1). Traditional decompressive management uses posterior fossa craniectomy, which has significant limitations and complication risks, including over-correction. A large single-stage craniectomy can lead to cerebellar ptosis and new or recurrent symptoms. Distraction of the posterior vault has been effective for relieving intracranial pressure in small case series. The authors present the largest series of patients with Chiari I malformations treated with posterior cranial vault distraction osteogenesis. Also introduced is a previously unpublished technique utilizing a vertical distraction vector for appropriate vault expansion while mitigating the risks of scaphocephaly and cerebellar ptosis.

Methods

This multi-center study included patients with syndromic and non-syndromic Chiari I malformations treated with vertical-vector distraction osteogenesis of the posterior cranial vault from 2008 to 2014. All patients had at least 1 year of follow-up except one who completed distraction but is currently in the consolidation phase. Demographic data, pre- and post-operative clinical symptoms, and perioperative details were assessed. Postoperative outcomes regarding aesthetics, complications, and symptomatic improvement were evaluated with neurosurgery.

Results

Nine patients were identified. Five had known syndromes, two likely had unidentified syndromes, and two were non-syndromic. Seven had prior Chiari-related surgeries. Most presented with hydrocephalus, motor symptoms, and developmental delay. Operatively, 2-3 internal distraction fixators were applied such that the vector of distraction followed a cephalad-caudad axis. Devices were activated on POD5 and distracted 1 mm/day. Three post-operative complications included a dislodged distraction arm, a device extrusion, and a local cellulitis. No complications affected the clinical outcome. All patients completed the distraction protocol. Radiographic follow-up showed excellent bone formation, decompression of the posterior fossa, and no cerebellar ptosis (Figure 2). Neurological surveillance showed improvement in intracranial pressure, hydrocephalus, motor symptoms, and behavioral problems.

Conclusion

The authors have presented here the largest experience to date of patients with Chiari I malformations treated with distraction osteogenesis, along with a novel technique to safely and effectively expand the posterior fossa while minimizing risk of cerebellar ptosis. Given the excellent functional, aesthetic, and clinical outcomes of this technique, it appears valuable as an initial or secondary operation for symptomatic Chiari I malformations.

Figure 1 Preoperative MRI

Figure 2: Post-Operative MRI