Pseudotumor cerebri a major factor in failure following surgery for the Chiari I malformation

Improving treatment outcome in the Chiari I malformation (CM1) depends on many factors; among the most important is the recognition of associated co-morbidities. A common associated condition is idiopathic intracranial hypertension, also known as pseudotumor cerebri (PTC).

In 2006, Fagan et al. of The University of Chicago Children’s Hospital in Chicago, Illinois published a milestone study recognizing the importance of considering this disorder in patients with CM1, especially as the body mass index of the U.S. population continues to increase.

The authors defined the problem and goal of their study –

“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.”

The records of 192 patients with CMI previously treated by posterior fossa decompression were reviewed. The 36 patients failing surgery had a lumbar puncture performed to measure their spinal fluid pressure. Of these, 15 patients (42%) were found to have elevated intracranial pressure consistent with pseudotumor cerebri; a high number that should serve to get this disorder on the radar of all healthcare providers caring with persons with CM1.

Of the 15 patients found to have the Chiari pseudotumor cerebri syndrome, 14 required subsequent treatment with a CSF shunt. Outcome following shunt placement varied depending on age of the patient: “Seven of 9 pediatric patients had significant symptom resolution while 6/6 adult patients remained variably symptomatic.”

The author’s concluded:  

“CM1 and PTC co-exist in a surprising percentage of failed operative CM1 patients and present with a syndrome that is difficult to treat.” (emphasis added)

Future posts will look further at this important syndrome including its presentation, diagnosis and treatment.


Fagan LH, Ferguson S, Yassari R, Frim DM.
The Chiari pseudotumor cerebri syndrome: symptom recurrence after decompressive surgery for Chiari malformation type I
Pediatr Neurosurg. 2006;42(1):14-9