Changes in ventricular size after endoscopic third ventriculostomy

Background. There is general consensus that a successful endoscopic third ventriculostomy is usually followed by a decrease of ventricular size without reaching their normal size. This study was performed to determine how the change related to clinical outcome, how it developed chronologically and whether the change in ventricular size was different in acute and chronic forms of hydrocephalus. Method. Fifty-five of 74 patients who had undergone endoscopic third ventriculostomy during the period 1997-2004 were selected by the criterion that they had both pre-operative and post-operative films and no neurosurgical manoeuvre other than a surgically successful endoscopic third ventriculostomy in the time span between both radiological studies. Ventricular size was measured with the Evans index, third ventricle index, cella media index and ventricular score. Median age was 51 years (interquartile range, 27-65 years). Results. The change in ventricular size detected shortly after surgery is related to clinical outcome for all ventricular ratios, except the cella media index (p = 0.08). When third ventriculostomy is clinically successful, there is a gradual decrease of ventricular size over a period of more than three months (p < 0.0001 for all ventricular ratios). The reduction is more prominent in acute hydrocephalus than in chronic forms for all ventricular ratios, except the Evans index (p = 0.12). The third ventricle exhibits the greatest reduction (25% with a 95% confidence interval: 15.4-34.5) and determines a different pattern of change in ventricular size after endoscopic third ventriculostomy between acute and chronic hydrocephalus. Conclusions. A decrease of the ventricular size detected soon after endoscopic third ventriculostomy is associated with a satisfactory clinical outcome. This response continues during the first few months after surgery. The reduction is more prominent in acute forms of hydrocephalus.