Defining sexual dimorphism in masculinizing chest surgery using 3-dimensional imaging.

There is no consensus on the ideal scar location and inframammary fold (IMF) placement in the gender-affirming double-incision mastectomy technique. Recent advances in imaging technology have facilitated noninvasive investigations into anatomic variability, in many cases, obviating the traditional approach of cadaveric dissection to answer anatomic questions. A better understanding of chest wall sexual dimorphism may allow surgeons who perform gender-affirming procedures to achieve more natural-appearing results. A total of 60 chests were analyzed using either cadaveric dissection (n = 30) or virtual dissection with 3-dimensional (3-D) reconstructions of computed tomography (CT) images (n = 30) using the Vitrea® software. Chest proportions were recorded using each technique, correlating surface anatomy with muscular and bony landmarks. Cadaveric and 3-D radiography chest analysis revealed that natal male chest walls are, on average, wider and longer than natal female chest walls. The pectoralis major muscle dimensions and the location of its insertion were not found to significantly differ between male and female chests. The male nipple-areolar complex (NAC) tended to be narrower in length and width, with a less projecting nipple than the female NAC. Finally, the IMF was found to lie over the interspace between the fifth and sixth rib in both male and female chests. Our findings confirm natal male and female IMF are positioned between the 5th and 6th ribs. This fact affirms the senior author's technique of masculinizing the chest, keeping the masculinized IMF at approximately the same level as the natal female IMF and following the pectoralis major muscle edges to define the resulting scar in a way that differs from previously reported techniques.