gms | German Medical Science

Objective: There is increasing evidence that patients with Chiari Malformations (CMs) also have disorders of intracranial pressure (ICP). The generally accepted treatment for patients with symptomatic CM is foramen magnum decompression (FMD). FMD carries a high rate of failure and complication. ICP dynamics in patients with persistent symptoms despite FMD have not been characterised. We sought to characterise the ICP dynamics of CM patients with persistent symptoms despite previous FMD.

Methods: Retrospective observational case-control study looking at ICP dynamics in patients with symptomatic CM, with and without previous FMD. All patients with CM were extracted from our department’s ICP database. Patients were divided into two groups: Virgin Chiari Malformation (VCM) and failed Foramen Magnum Decompression (fFMD). Both groups were compared with a control group consisting of patients with normal ICP dynamics. We excluded patients with a CSF shunt system. Median ICP (mICP) and median pulse amplitude (mPA) were compared between the three groups.

Results: We identified 45 patients with Chiari malformations and ICP monitoring data. 12 were excluded for having an existing CSF diverting shunt. Of the 33 patients included, 22 were assigned to the VCM group and 11 were assigned to the fFMD group. All 11 fFMD patients were undergoing investigation for persistent symptoms. The control group consisted of 42 patients. mICP in the control group was 3.24 ± 2.99mmHg (mean ± standard deviation). mICP in the VCM group was 3.82 ± 3.74mmHg (no significant difference to controls). mICP in the fFMD group was 3.04 ± 8.26mmHg (no significant difference to controls). mPA in the control group was 4.14 ± 1.30mmHg. mPA in the VCM group was 5.50 ± 2.06mmHg (significantly higher than the control group t=3.24, 95% CI = 0.52 – 2.20mmHg, p=0.002). mPA in the fFMD group was 5.47 ± 1.81mmHg (significantly higher than the control group t=2.79, 95% CI = 0.37 – 2.29mmHg, p=0.007).

Conclusions: Patients with CM exhibit increased ICP pulsatility, which is a measure of compliance. Untreated CM patients have similar overall mICP to normal patients, but significantly higher mPA. Whether increased mPA is part of the underlying pathophysiology of the development of CMs, or is a consequence of a posterior fossa anatomical variation, is yet to be established. It is possible that a spectrum exists between the two scenarios. Patients with persistent symptoms following FMD demonstrate persistently raised mPA, implying that either FMD has been inadequate or that despite adequate decompression, there is an ongoing persistent underlying abnormality of mPA. Whether the increased pulsatility is responsible for ongoing symptoms or not is yet to be investigated. CSF diversion may be a potential primary or secondary intervention to reduce mPA in patients with CM. Further research is required to see if this correlates to symptomatic improvement.