Mesocolon

The mesocolon is a double layer of peritoneum that suspends portions of the colon from the posterior abdominal wall and conveys the associated blood vessels, lymphatics, and nerves. It is a crucial anatomical structure that ensures mobility of the colon while anchoring it in place and facilitating its vascular and neural supply. Depending on the region of the colon it attaches to, the mesocolon is named accordingly — such as the transverse mesocolon or sigmoid mesocolon.

Structure

The mesocolon is formed by two layers of visceral peritoneum that enclose fatty connective tissue, blood vessels, lymphatics, and autonomic nerves. These layers extend from the posterior abdominal wall to the corresponding part of the colon. Each part of the mesocolon has a root where it attaches to the posterior wall and a free edge connected to the colon itself.

• Transverse mesocolon: Connects the transverse colon to the posterior abdominal wall. It is continuous with the posterior layer of the greater omentum and crosses the pancreas horizontally.
• Sigmoid mesocolon: An inverted V-shaped fold that attaches the sigmoid colon to the posterior pelvic wall. Its root is narrow but allows for considerable mobility of the sigmoid colon.
• Ascending and descending colon: Typically considered secondarily retroperitoneal and lack a true mesocolon, although remnants may exist, especially in infants or variant anatomy.

Contained within the mesocolon are:

• Branches of the superior and inferior mesenteric arteries
• Mesocolic lymph nodes
• Autonomic nerve fibers from the superior and inferior mesenteric plexuses
• Lymphatic vessels that drain the colon

Location

The mesocolon is located in the posterior abdominal cavity, with its various parts extending between the colon and specific areas of the posterior abdominal or pelvic walls:

Its position creates important compartments within the peritoneal cavity and helps define spaces such as the supracolic and infracolic compartments, especially with the transverse mesocolon acting as a horizontal divider.

Function

The mesocolon serves several critical functions in the abdominal cavity:

• Suspension and stabilization: Maintains the position of the colon while allowing limited movement during digestion.
• Pathway for vessels and nerves: Acts as a conduit for arterial branches, veins, lymphatics, and autonomic nerves to reach the colon.
• Lymphatic drainage: Contains mesenteric lymph nodes important for immune surveillance and drainage of the colon.
• Compartmentalization of the peritoneal cavity: Helps define anatomical zones relevant to fluid collection, infection, or surgical access.

Clinical Significance

Understanding the mesocolon's structure and positioning is essential in various clinical and surgical scenarios:

• Colon cancer surgery: During oncologic resections such as right hemicolectomy or sigmoid colectomy, the mesocolon must be carefully dissected to remove lymph nodes and preserve or ligate the vascular supply.
• Internal hernias: Rarely, defects or abnormal openings in the mesocolon (especially the transverse mesocolon) can allow loops of intestine to herniate through, potentially causing bowel obstruction.
• Peritonitis and abscesses: The mesocolon can act as a barrier or conduit for the spread of infection or pus in intra-abdominal infections. For example, the transverse mesocolon may help localize an abscess in the supracolic compartment.
• Ischemic colitis: Vascular compromise within the mesocolon’s arterial supply can result in localized ischemia to parts of the colon, especially the splenic flexure or sigmoid regions.

In recent years, the concept of the mesocolon as a continuous mesentery has been proposed, suggesting a reclassification of mesenteric anatomy and its surgical relevance. This has implications for standardized surgical planes during complete mesocolic excision in colorectal cancer treatment.