There is no fusion fascia in the abdomen and extraperitoneal fascia always surrounds the mesentery.

Toldt's fascia has always been described as a fusion fascia formed by two layers of visceral peritoneum when the mesentery attaches to the posterior abdominal wall. However, there is still no consensus about the mesentery and its surrounding fascia based on the current anatomic theories. This study aimed to determine the anatomical structures of the abdomen and provide a correct surgical plane for mesenteric‐based surgery. Surgical videos of 121 patients who underwent laparoscopic operations of the digestive tract were reviewed to identify and compare the anatomical structures of the mesentery and associated fascia. Twenty‐one postoperative specimens were stained with hematoxylin and eosin to indicate the histological appearance of the mesentery and its surrounding fascia. Furthermore, dynamic models had been established to explain the formation mechanism of the associated histological structures in different regions during the progression of mesenteric attachment. The fasciae surrounding the mesentery, including the submesothelial connective tissue, the subserosal connective tissue, Toldt's fascia, and "angel hair," have the same histological characteristic to extraperitoneal fascia. The general anatomical structure of the abdomen can be divided into three layers (abdominal wall, urogenital system, and digestive system) and two interlayers (transversalis fascia and extraperitoneal fascia). The extraperitoneal fascia surrounds the entire digestive system and is the natural layer separating adjacent structures from each other. Typical histological structures in the regions of posterior attachment include the fascia propria of the mesentery, mesofascial plane, extraperitoneal fascia, retrofascial plane, and anterior renal fascia. The urogenital system is surrounded by similar histological structures. There is no fusion fascia in the abdomen due to retreat of the visceral peritoneum, and all of the fasciae surrounding the mesentery are extraperitoneal fascia. This study demonstrates that the typical histological structures in the regions of attachment and mesofascial plane are the correct anatomic interface for mesenteric‐based surgery. [ABSTRACT FROM AUTHOR]