Chiari I malformation: a rare cause of noncommunicating hydrocephalus treated by third ventriculostomy

Object. Hydrocephalus associated with Chiari I malformation is a rare entit y related to an obstruction in the flow of cerebrospinal fluid (CSF) in the foramen of Magendie. Like all forms of noncommunicating hydrocephalus, it can be treated by endoscopic third ventriculostomy (ETV). The object of thi s study is to report a series of five cases of hydrocephalus associated wit h Chiari I malformation and to evaluate the use of ETV in the treatment of this anomaly. Methods, Five patients (four women and one man with a mean age of 29.6 year s) underwent ETV for hydrocephalus associated with Chiari I malformation be tween April 1991 and February 1997. All patients had presented with paroxys mal headaches, which in two cases were associated with visual disorders. Al l patients had also presented with hydrocephalus (mean transverse diameter of the third ventricle 12.79 mm; mean sagittal diameter of the fourth ventr icle 18.27 mm) with a mean herniation of the cerebellar tonsils at 13.75 mi n below the basion-opisthion line. Surgery was performed in all patients by using a rigid endoscope. No complications occurred either during or after the procedure, except in one patient who experienced a wound infection that was treated by antibiotic medications. The mean duration of follow up in this study was 50.39 months. Four patient s became completely asymptomatic and remained stable throughout the follow- up period. One patient required an additional third ventriculostomy after 1 year, due to secondary closure, and has remained stable since that time. P ostoperative magnetic resonance images demonstrated a significant reduction in the extent of hydrocephalus in all patients (mean transverse diameter o f the third ventricle 6.9 nun [p = 0.0035]; mean sagittal diameter of the f ourth ventricle 10.32 nun [p = 0.007]), with a mean ascent of the cerebella r tonsils from 13.75 nun below the basion-opisthion line to 7.76 nun below it (p = 0.01). In addition, CSF flow was identified on either side of the o rifice of the third ventriculostomy in all patients postoperatively. Conclusions. Results in this series confirm the efficacy of ETV in the trea tment of hydrocephalus associated with Chiari I malformation. It is a relia ble, minimally invasive technique that also provides a better understanding of the pathophysiology of this malformation.