Introduction: Lumboperitoneal (LP) shunting has been used as a treatment option for cerebrospinal fluid (CSF) diversion in the setting of patients with pseudotumor cerebri also known as idiopathic intracranial hypertension (IIH). One of the potential complications with the procedure is the development of an acquired Chiari malformation, type I (CM).

Methods: A retrospective chart review of adult patients diagnosed with IIH who underwent an initial CSF shunt diversion surgery from from 2003 - 2008 was performed. We reviewed the incidence of acquired Chiari malformation in 35 consecutive patients who received lumboperitoneal shunts as part of their management. All had preoperative imaging showing normal anatomy at the foramen magnum with no evidence of cerebellar tonsilar descent.

Results: Ten of the 35 (29%) patients developed CM following shunt placement. Time to onset varied between 3 months and 6.5 years. Seven patients underwent further surgeries (range 1 to 14). Three patients did not. Five patients (14%) underwent sub occipital decompressions from 4 months to 4.7 years following radiographic diagnosis.

Conclusions: CSF diversion in patients with IIH is associated with a known potential for revision surgery. LP shunting is known to be a risk factor for development of CM. In our current small series, the incidence of radiographic CM was 29%. The incidence of symptomatic CM requiring suboccipital decompression was 14%. These figures should be taken into account when recommending CSF diversion in this patient population.

Patient Care: We hope to provide a measure of the risk for acquired Chiari malformation in patients undergoing LP shunts for IIH.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of potential development of the acquired Chiari malformation in patients with IIH treated with LP shunting

References: Chumas, PD et al (1993). Tonsillar herniation: The rule rather than the exception after lumboperitoneal shunting in the pediatric population. Journal of Neurosurgery, 78(4), 568-573. Payner, TD et al (1994). Acquired chiari malformations:Incidence, diagnosis, and management. Neurosurgery, 34(3), 429-434. Wang, VY et al (2007). Complications of lumboperitoneal shunts. Neurosurgery, 60(6), 1045-1048. McGirt MJ, et al. (2004) Cerebrospinal fluid shunt placement for pseudotumor cerebri-associated intractable headache: predictors of treatment response and an analysis of long-term outcomes. J Neurosurg. 101(4):627-32.