Influence of the shunt type in the difference in reduction of volume between the two lateral ventricles in shunted hydrocephalic children.

Introduction: After shunt insertion there is commonly a disproportionate reduction in size of the lateral ventricle containing the catheter (shunted lateral ventricle), which is almost certainly related to shunt function. To explore the difference between two shunt types, the Differential Pressure Medium Pressure cylindrical (M.P.) and Delta 1.5 valves (manufactured by P.S. Medical, Goleta, CA, USA), we measured lateral ventricle volumes preoperatively and after 3 months, using segmentation techniques on CT or MR scans.

Materials And Methods: There were 40 patients (mean age 65.7 months), 17 with M.P. and 23 with Delta valves. There were 22 new shunts (8 M.P. and 14 Delta), and 18 revisions (9 M.P. and 9 Delta). Shunted to non-shunted ventricle volume ratios and the difference in ratios (preoperative to 3 months) was calculated. A ratio considerably less than 1 would indicate disproportionate reduction in the volume of the shunted ventricle in comparison to the non-shunted one.

Results: In the new shunt group, the preoperative ratio was 1.63 for M.P. and 1.07 for Delta (p=0.148, one-way ANOVA). The 3-month ratio was 0.71 for M.P. and 1.44 for Delta. The difference in ratios was 0.91 for M.P. and -0.36 for Delta (p=0.042, one-way ANOVA). There were 4 shunt obstructions in this group (3 with M.P. and 1 with the Delta valve). In the revision group, the preoperative ratio was 0.85 for M.P. and 0.88 for Delta (p=0.859, one-way ANOVA). The 3-month ratio was 0.74 for M.P. and 0.60 for Delta. The difference in ratios was 0.11 for M.P. and 0.27 for Delta (p=0.274, one-way ANOVA). There were 5 shunt obstructions in this group (2 with M.P. and 3 with the Delta valve). No correlation was found between incidence of shunt obstruction and shunt type or ventricular volume ratio difference (preoperative to 3 months) in either of the two operation groups.

Conclusions: Following new shunt insertion, the presence of a differential pressure valve results in early significant reduction in the shunted lateral ventricle volume. This may predispose to shunt obstruction although this study has not proven this. This effect was not observed with the Delta valve after 3 months. Following shunt revision, no difference between the two valve types was observed. This may indicate a chronic effect of the presence of a shunt on the ventricular system size, obviating the effect of different shunt types.