The most ideal surgery for rectal cancer is to eradicate the tumor and preserve the anus at the same time. However, traditional rectal cancer surgery emphasizes the distance between the lower edge of the tumor and the anal opening, and it is believed that any rectal cancer 5-6 cm away from the anal opening should be removed from the anus. Recently, European and American scholars have proposed two new concepts, total mesorectal excision (TME) and total rectal excision (TRE), which have revolutionized the surgical treatment of ultra-low rectal cancer (i.e., the lower end of the tumor is less than 4 cm from the anal opening) and enabled the majority of patients with ultra-low rectal cancer to preserve the anus. The theoretical basis of TRE surgery: (1) complete removal of the internal rectal sphincter (the thickened muscle layer of the lower rectum forms the internal rectal sphincter), as long as the external rectal sphincter is preserved, the normal defecation function of the anus can be preserved; (2) whether the anus can be preserved in low-grade rectal cancer is not related to the location of the tumor, regardless of how far the rectal tumor is from the anal opening, as long as the tumor does not penetrate the rectal ring (internal rectal sphincter), the anus can be preserved. ), the anus can be preserved. The anatomical basis of preserving the anus in low rectal cancer is explained by the following illustrations: Figure 1 The lower rectum is thickened into the internal sphincter, which can be partially or completely removed (left click on the picture to enlarge it, same as below) Figure 2 The external anal sphincter is divided into 3 parts, which form a ring-shaped structure called the rectal ring, and its integrity needs to be preserved during surgery Figure 3 The relationship between the external anal sphincter and the rectal anal canal Figure 4 The anatomical structure of the rectal anal canal Figure 5 Low rectal cancer invaded the sacrum but not the rectal ring, and successful anus-preserving surgery was performed