1288. Acquired cerebellar tonsillar herniation after cystoperitoneal shunting of cranial arachnoid cysts in pediatrics

Authors: Muhammad Burhan Ud Din Janjua, MD; OF Owagbemi, MD; Dale Swift, MD (Dallas, TX)

Introduction: Cerebellar tonsil herniation (CTH, Chiari I malformation) has been reported as acquired condition following shunt placement for intracranial arachnoid cysts. The incidence and predictive variables of this unusual complication have not been determined. Methods: We reviewed the medical records of 59 patients who underwent shunting procedures for intracranial arachnoid cysts to determine if CTH developed post-operatively. Measured variables included patient age, cyst size and location, shunt valve pressure, intracranial catheter location (within the cyst versus subdural) and degree of cyst reduction. Paired and upaired t-tests were utilized for statistical analysis. Results: Of 59 patients who underwent shunt procedures for arachnoid cysts, 45 (76%) had the proximal catheter placed within the cyst (CPS), and 12 (21%) had the proximal catheter placed in the subdural space (SDS). (Two patients (3%) had ventriculoperitoneal shunts placed.) The patients who received SDS all had pre-operative subdural fluid collections either from spontaneous rupture of the arachnoid cyst (10 patients, 83%) or as a result of prior operative fenestration (2 patients, 17%).None of the patients undergoing SDS developed CTH. Sixteen of the patients (36%) who received CPS developed CTH. CTH was generally apparent by one year post-operatively.Interestingly in 3 (8%) patients, reduction in CTH was observed in cases of CPS occlusion. Conclusion: The development of CTH roughly correlated with the degree of cyst reduction and younger patient age. Cerebellar tonsil herniation (acquired Chiari malformation) may occur more frequently than previously appreciated after cystoperitoneal shunt placement. CSF overdrainage may play a significant role in this pathogenesis.