The Chiari pseudotumor cerebri syndrome: symptom recurrence after decompressive surgery for Chiari malformation type I

Introduction: The etiology of Chiari malformation type I (CM1) as well as other anomalies associated with CM1 remains poorly defined. We have noted the presence of elevated CSF pressures with small ventricles, consistent with the pseudotumor cerebri (PTC) syndrome in a group of CM1 patients that did not respond over the long term to posterior fossa decompression. In order to better understand this association, we reviewed a series of CM1 patients treated by posterior fossa decompression to define the prevalence and nature of post-Chiari PTC.

Methods: We performed a retrospective chart review of 192 patients diagnosed with CM1 and treated by posterior fossa decompression. Patients who failed to respond to surgery were evaluated by CINE MR flow studies to assess presence of CSF flow at the foramen magnum and then by lumbar puncture if flow was present. The diagnosis of Chiari PTC was defined by recurrence of Chiari-like symptoms after decompression, elevated lumbar CSF pressure in the absence of ventriculomegaly, and transient resolution of symptoms with large volume lumbar CSF drainage.

Results: Thirty-six of 192 patients did not improve with surgical decompression. Fifteen of 36 operative CM1 patients (41.6%) were found to have Chiari PTC. The most frequent symptoms of CM1/PTC patients were head pain, body aches, and balance difficulties. Three patients also experienced visual complaints. The mean maximum lumbar CSF pressure documented in this cohort was 26 cm of water in adults and 25.3 in children. All patients received treatment for the CM1/PTC that culminated with CSF shunt placement in 14/15. Seven of 9 pediatric patients had significant symptom resolution while 6/6 adult patients remained variably symptomatic.

Conclusion: CM1 and PTC co-exist in a surprising percentage of failed operative CM1 patients and present with a syndrome that is difficult to treat. The etiology of this association after Chiari decompression is unclear, though perhaps posterior fossa surgery in the setting of abnormal anatomy and potentially anomalous CSF flow dynamics contributes to CSF malabsorption and resultant or coexistant PTC.