• Edward W Dyson, Aswin Chari, Ahmed K Toma, Lewis W Thorne, and Laurence D Watkins.
• Victor Horsley Department of Neurosurgery, National Hospital for Neurology and Neurosurgery, Queen Square, London, United Kingdom.
• Neurosurgery. 2020 Jun 1; 86 (6): E552-E557.

BackgroundThe standard treatment for symptomatic Chiari malformation (CM) I is foramen magnum decompression (FMD) to facilitate cerebral spinal fluid flow through the foramen magnum, improve intracranial compliance, and alleviate symptoms (commonly headache). This procedure has a variable success rate, with a significant proportion of patients having persistent symptoms after surgery.ObjectiveTo investigate intracranial pressure (ICP) hydrodynamics in symptomatic surgery-naïve patients with CM I and symptomatic patients who have had prior FMD.MethodsWe undertook a retrospective, observational cohort study, extracting data from our departmental ICP database. Patients with untreated ("Virgin") Chiari malformations (VCM), patients with previous "failed" FMD (ie, with persistent classical Chiari symptoms) (fFMD) and a normal control group, all with existing continuous ICP monitoring date were included. Median ICP (mICP) and median pulse amplitude (mPA) were compared between the groups.ResultsA total of 33 CM patients (22 VCM and 11 fFMD) and 42 normal controls were included for analysis. mICP did not differ significantly between the normal control, VCM, and fFMD groups. mPA in the VCM and fFMD groups was significantly higher than the control group (P < .01 and P < .05, respectively).ConclusionIn this cohort, patients with persistent symptoms after FMD have persistently impaired intracranial compliance, similar to patients who have not undergone surgery at all when compared with a control group. The reasons for this are not clear, and further research is required to establish the causation and optimum management for failed FMD.Copyright © 2020 by the Congress of Neurological Surgeons.

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