A Comparison of Manual and Three-Dimensional Modalities in Predicting Nellix Polymer Volume.

Purpose: Achieving an effective seal with the Nellix endovascular aneurysm system is dependent on filling the stent bags with an appropriate volume of polymer. Calculating this volume preoperatively is essential and can be performed manually or using three-dimensional (3D) software. The aim of this project was to compare the accuracy of these two methods relative to the actual polymer volume used.

Materials and Methods: Consecutive patients undergoing Nellix aneurysm repair were included in this retrospective study. Operation notes were analysed for the polymer volume used intra-operatively. Predicted volumes for all patients had been calculated on picture archiving and communication system (PACS) using a manual 'segmental cylinder' method. Computed tomography angiograms were then re-analysed using the Synapse 3D PACS update. The difference between groups was assessed using a paired t-test.

Results: Twenty-eight patients were included in the analysis; 26 men (92.9%) and 2 women (7.1%); median age 80.9 years (interquartile range, 72.5-84.5 years). The mean volume of polymer used was 103 mL. The mean manual-derived prediction was 100.1 mL (P=0.365) and 3D-derived prediction 110.2 mL (P<0.001). Manual prediction led to an average 2.8% underestimate of polymer volume whilst 3D prediction led to an average 7.0% overestimate.

Conclusion: Calculating predicted polymer volume for the Nellix system is more accurate using a manual approach then the 3D alternative. Whilst this method is more time-consuming, there is no significant difference when compared to the actual volume used. Quicker 3D software predictions can be utilised, but their tendency to overestimate should be recognized and taken into account during planning.