The triangular prism approximation method for volume estimation of deep inferior epigastric artery perforator flap in breast reconstruction

Background Many methods to predict the amount of tissue needed for breast reconstruction have been reported, but some require complicated software and special systems. The purpose of this report was to present a simpler method for predicting the volume required for deep inferior epigastric artery perforator (DIEP) flaps. The accuracy of this method was evaluated based on both actual flap design and computed tomography. Methods The weight and horizontal (x cm) and vertical (y cm) lengths of the DIEP flap were recorded, and the maximum thickness of subcutaneous tissue (z cm) was measured from computed tomography in 36 cases of breast reconstruction using DIEP flap in our hospital performed between January 2019 and December 2020. Flap volume was calculated using three methods of approximation: triangular prisms using physical and CT measurements (1/2xyz cm(3)); quadrangular and triangular prisms using physical and CT measurements (3/4xyz cm(3)); and a previously reported method using measurements from CT angiography alone and calculation with a standard mathematical formula. These three groups were compared using Bland-Altman plots and intraclass correlation coefficients (ICCs) to assess consistency between predicted and measured values. Results On Bland-Altman plots, values were distributed almost randomly around the average value of the difference, and no proportional error was evident in the methods. The ICC between predicted and actual values of triangular prisms using physical and CT measurements was largest: ICC (1, 2) = 0.978 (0.825-0.981; 95% confidence interval for ICC). A sufficient flap volume was able to be transplanted in all cases. Conclusion The methods presented appear useful to calculate flap volume closer to the measured value without complicated software systems. These results suggest that the method using two symmetric triangular prisms could predict volume more easily than previously reported methods and may facilitate good breast reconstruction.