The aortic wall has a thin intima, a thick media, and a loose adventitia. The media is composed of dozens of parallel lamellar units. Each lamellar unit contains an elastic lamella and adjacent smooth muscle cells and matrix [1]. Aortic dissection is usually defined as the separation of the medial lamellar units (Fig. 1). In most cases of aortic dissection, there is a break in the intima and the inner medial layer. The break is called “intimal tear.”

The pathogenesis of aortic dissection is unclear. It is postulated that blood is pumped through the intimal tear into the media by pressure, and the aortic wall is separated into two layers along a dissection plane [2], [3], [4], [5]. We name this hypothesis the hypothesis of medial splitting.

Pathologists noticed that the dissection plane was usually located in the outer third of aortic media [6], [7]. However, to our knowledge, no study had ever precisely measured the depth of dissection plane. In this study, a survey was performed to investigate the distribution of the depth of dissection plane and its correlation with other clinical and pathological parameters to help understand and expand the current knowledge of aortic dissection.